The (e,2e) spectrometer vacuum chamber (figure 1) is manufactured from 304 grade stainless steel, the construction being carried out by Vacuum Generators using a design of Jones, Read and Cvejanovic, full details of which may be found in T. 3mm thick mu-metal magnetic shielding is placed both internally and externally to decrease extraneous external magnetic fields to less than 5mG at the interaction region. All inputs and outputs to the spectrometer pass through the vacuum chamber via feedthroughs on the top flange. The top flange of the vacuum system is a 25mm stainless steel flange with 11 conflat CF70 flanges arranged around a central 200mm flange designed for locating a hydrogen source.
Two flanges are used for the high voltage channeltron and photomultiplier tube inputs and pulse outputs.
Three rotary motion feedthroughs allow the analysers and electron gun angles to be changed externally via stepper motors for both analysers and for the electron gun.
The ionisation gauge is placed at right angles to the main flange to prevent light from the thoriated iridium filament entering the vacuum system, which would increase noise on the photomultiplier tube. The ionisation gauge feedthrough is sooted, and a loose cover is placed over the entrance in the chamber flange to prevent stray light from the ion gauge entering the vacuum system. The target gas enters the system via a CF70 flange which has two 6mm stainless steel tubes welded into the flange. The other gas feed is connected to a hypodermic needle set at 90A° to the incident beam for measurements in other geometries.
The gas jet which is not currently used in the interaction region can be used to non-locally fill the chamber with gas for background counting measurements. The final CF70 flange is used when the photomultiplier tube is cooled, usually during baking of the system following exposure to atmosphere. The tube is cooled by passing vapour from a liquid nitrogen source through expansion coils wrapped around the photomultiplier tube housing.
The electron gun is a two stage non-selected gun designed by Woolf (Ph.D thesis, University of Manchester) (see figure 3). The gun consists of a filament, grid and anode source which is focussed using a triple aperture lens through two 1mm defining apertures in the centre of the gun.
The apertures define the electron beam pencil and beam angles, and are focussed onto the interaction region using a second triple aperture lens located between the apertures and interaction region. The electron gun is shielded using advance (constantin) sheet which is grounded to the body of the gun mounting. The gun is mounted onto an x-y translation table to allow placement of the electron beam as accurately as possible to the centre of rotation of the analysers and electron gun rotation axis. The gas jet is mounted from the electron gun using a narrow support of 310 stainless steel, and the Faraday cup can be attached to this support. The original unselected electron gun built by Woolf was completely rewired and a custom built PTFE 25 way inline wire-wrap plug and socket was placed between the 52 way vacuum electrical feedthrough and the electron gun. The wiring from the 52 way feedthrough to the inline plug is shielded colour coded 30 awg PTFE coated advance wire, and the inline plug and socket connectors are non-magnetic gold plated wire wrap pins. The electron analysers are constructed from molybdenum and are mounted from two rotating gear plates controlled externally via the rotation feedthroughs on the top flange (see figure 2).
The input electrostatic lenses for each analyser are three element cylindrical lenses as shown in figure 4. The interaction region is focussed onto the entrance aperture of the hemispherical energy analysers with a beam angle of around zero degrees, the image of the analyser entrance aperture being larger than the size of the interaction region.
Field gradients around the input and exit apertures are corrected using standard Jost correctors. The energy selected electrons passing through the exit apertures are finally collected by Mullard X919BL channel electron multipliers which amplify the single electron to produce a current pulse at their output.
A principle source of noise on the signal pulses arises from the turbo-molecular pump motor. The noise from the turbo pump is reduced to ~ 5mV using these techniques, and as the average pulse height from the saturated multiplier is around 20-40 mV, this allows adequate discrimination following amplification. The pre-amplifiers located external to the vacuum system are commercial 100X preamplifiers with 400pS rise-times, manufactured by Phillips Scientific.
The NIM signals produced by the discriminators drive two ORTEC 437 Time to Amplitude Converter's via appropriate delay cables and an ORTEC pulse delay unit. The main TAC output feeds an ORTEC Multichannel Analyser card located in the PC controlling the experiment, whereas the second monitor TAC drives an external MCA, allowing convenient monitoring of the coincidence signal as the experiment progresses. The high voltage supplies to the electron multipliers are two Brandenberg 5kV supplies controlled by the main PC via serial DAC's. Principally the filter is used to reduce pickup noise from entering via the HT cable onto the multiplier output. Secondly, the filter has a slow response time for high voltage spikes, and reduces the probability of damage to the pulse electronics should the EHT supply suddenly turn on or off. Capacitor C2 decouples the 1kW load resistor to earth for high frequency pulses from the CEM's, and the voltage appearing across this load is connected via the capacitor C3 to the input of the 6954 preamplifier.
Since the input impedance of the preamplifier is 50W and the CEM is effectively an ideal constant current supply, most of the current passes through to the preamplifier.
Finally, the 10M resistor prevents the output to the preamp from rising above ground when the preamp is disconnected from the circuit and is therefore a safety device for the preamplifier when initially connected. The original design placed the atomic beam nozzle and Faraday cup on the same support structure fixed to the body of the electron gun, with the atomic beam direction being in the detection plane when the perpendicular plane geometry is chosen (see figure 2). A second configuration is adopted for exclusively perpendicular plane coincidence experiments, the atomic beam nozzle being oriented at an angle of 45A° to the detection plane so that the gas effusing from the nozzle does not fill the analysers when they oppose the nozzle (see figure 6).
In this configuration the support strut for the atomic beam nozzle is terminated lower than the detection plane, as is the nozzle itself. For non-perpendicular plane measurements the Faraday cup is once mounted from the support strut and the gas effuses perpendicular to the electron beam direction. One difficulty when aligning an (e,2e) coincidence experiment lies in the focussing the incident electron beam and analysers onto the interaction region.
The throughput of electron current as detected by the Faraday cup is insensitive to both position and focusing of the electron beam, since the cup opening is usually made quite large (in this case 6 - 10mm) and the bias voltage applied to the cup to prevent electrons returning to the interaction region allows all electron trajectories within this opening to be detected. Conventionally, following maximisation of the Faraday cup current, the beam is steered and focussed onto the gas jet as detected by counts in the analysers.
This has the disadvantage that the overlap volume is maximised for both atomic and electron beam density, which tends to place the interaction volume as close as possible to the output of the atomic beam nozzle, which is almost certainly not in the centre of the detection plane. To eliminate the need for time consuming iterative techniques and the associated errors due to detection geometry, a separate method for tuning the electron gun is adopted that does not depend upon the analysers.
The interaction between the target and the electron beam not only produces ionisation, but the valence states of the target also are excited with various probabilities depending upon the incident energy of the electron beam.
These photons are detected by the photomultiplier tube, by placing a 450nm A± 50nm optical filter in front of the photocathode.
The interaction region is therefore defined where an aperture in front of the photocathode is focused by the lens.
The plano-convex focussing glass lens is covered by a grounded fine tungsten mesh to eliminate surface charging. The photomultiplier tube may be cooled by circulating nitrogen gas boiled off LN2 through copper coils encircling the photomultiplier tube housing. The photomultiplier tube used in the experiment is a 9789QB EMI photomultiplier tube with a bi-alkali photocathode peaking in the blue region of the optical spectrum. As with the electron multiplier circuitry, it is important to optimise the load of the photomultiplier tube so that reflections along the feeder line to the counting electronics are minimised.
The 1nF 6kV capacitors across the dynodes close to the output stage are used as charge storage pumps that quickly refurbish the surface charge on the dynodes, allowing increased counting rates. The dynode resistors are 1% tolerance metal film resistors as these are more stable with temperature. The EHT supply to the photomultiplier tube is a Brandenberg 2kV supply operating at 1500V for this tube. The negative going output pulses from the tube measure typically 200-500mV in height, and therefore are able to directly drive an ORTEC 473A constant fraction discriminator located in one of the NIM crates.
All resistors and capacitors for the dynode chain are soldered to the photomultiplier tube base internal to the vacuum system, using standard 5-core solder.
Typical pulse heights from the electron multipliers in saturation mode are 25-40mV, whereas the typical height of the photomultiplier tube pulses is of the order of 250mV. The electron multiplier pulses are obtained from the multiplier supply circuitry as explained above. The amplified pulses from the 6954 amplifiers pass along doubly shielded RG-58 cable to the input of the ORTEC 473A discriminators. The two analyser discriminators are located in separate NIM crates to increase isolation and reduce common mode pickup. The slow rise-time positive outputs from the 473A discriminators pass to three ORTEC 441 rate-meters which allow counting and monitoring of the pulses.
The fast NIM pulses from the analyser 473A CFD's pass through appropriate delay lines to two 437 TAC's. This second multichannel analyser allows the operator to monitor the total accumulated coincidence signal during operation.
The lens supplies that control the voltages impressed onto the lens elements and deflectors in the experiment were developed over a number of years, and therefore take different forms.
Three of these supplies feed the deflectors in the electron gun, the other two supply the input deflectors in the analysers.
In a second 19" crate is located the gun lens high voltage supplies together with the high voltage supplies for the Faraday cup.
In a third 19" crate is located the analyser voltage supplies together with a set of serial loading supplies that control the electron multiplier EHT supplies. A further supply controls the current boost circuitry located in the filament constant current supply unit (see below). The outputs of each computer controlled supply that drives an individual lens element or deflector are connected to a 70 relay switching board. The Digital voltmeter is in turn accessed via an IEEE-488 interface which is addressed by an 8086 slave PC which converses with the central PC which controls the experiment. The outputs from the relay board connect to the spectrometer via shielded multicore cables which take the gun voltages to the 52 way feedthrough and the analyser voltages to the two 19 way feedthroughs located on the vacuum flange.
The gun supply multicore also carries the filament supply current to the 52 way feedthrough. The Faraday cup current is measured by the Keithley Digital voltmeter when under computer control but this can also be measured by an external pico-ammeter. In addition to the analyser electrostatic lens and deflector voltage connections, the 19 way CF70 feedthroughs are used to control signals from internal sensing opto-isolators which control the stepper motor interlocks. The stepper motors that drive the analysers and electron gun around the detection plane are five phase motors with integral 10X reduction gearboxes driving the rotary motion feedthroughs. The intelligent stepper motor drivers are addressed via a serial port located on the controlling PC bus. An additional interference problem was traced to the RS232 serial line from the controlling PC. The PC bus was found to be poorly earthed due to very little copper being used for the bus earth. This was cured by decoupling the 0V RS232 line from the main 0V line for the stepper motors, as is shown in figure 10. The analyser stepper motor supplies have a facility for halting the motors using limit switches which are optically coupled to the internal 68000 logic circuits driving the supplies. The SD5443-3 phototransistor normally illuminated by the TEMT88PD photodiode during operation ensured a fail-safe mechanism should any of these components fail (this automatically prevent the motors from running). Should the analysers move into a position as defined by the four criteria (a) - (d) above, a shutter located on the analyser turntables moves between the appropriate photodiode and phototransistor, shutting off the light and thereby shutting down the stepper motor current.
Only motion in the opposite direction is allowed by controlling logic, allowing the analyser to move away from the point of imminent collision but no closer. The six pairs of optocouplers that prevent the analysers moving into the Faraday cup, electron gun and gas jet support are located on the mounting struts supporting the main body of the spectrometer. Two optocouplers are located on the side of analyser 2, and two shutters are located on the sides of analyser 1 to prevent the analysers colliding with each other. Finally a ninth optocoupler is located over the electron gun counterweight which monitors when the gun is at an angle less than 65A°, where the sweep angle around the detection plane is reduced. The current boost circuit operates from a serial driven supply card as detailed previously.
The main filament drive is through six power diodes that feed the current from the constant current supply to the filament. The Darlington transistor T1 feeds additional current to the filament via three parallel 10 turn 100W trim resistors through a 1N4007 diode.
As the constant current supply acts as an infinite resistance source, the boost circuit supplies additional current only when the voltage at the anode of the feed 1N4007 exceeds the output voltage of the constant current supply. Finally, the filament bias voltage (and hence energy of the electrons) is set to the midpoint of the filament by two 100W balancing resistors located across the terminals.
In addition to the ADC buffer card, three independent isolated regulated supplies drive REF01 voltage reference sources for measurement of the positions of 10 turn potentiometers located on the analyser and electron gun rotary drive shafts. The angular position of the electron gun and analysers is calibrated when the system is opened using visible laser diodes that define these angles to an accuracy of A±0.2A°. Figure 13 shows an overall block diagram detailing the computer control and high speed pulse interfacing to the spectrometer.
GOFAR Services, LLC - Appliance Repair Houston, TX - Chapter 4COMPRESSOR IS RUNNINGBUT REFRIGERATOR IS NOT COLDCOMPRESSOR IS RUNNING BUT REFRIGERATOR IS NOT COLDBefore you perform any of the other tests in this chapter, make sure that the compressor is running.


One of these is internally connected to a gas jet which can be set at 45A° to the incident electron beam and is used in the perpendicular plane experiments. These stainless steel feeder tubes are connected to the nozzle using grounded shielded PTFE hose. One follows the anode, another corrects the beam direction between the apertures and a third steers the beam onto the interaction region. This shield is coated with aerodag colloidal graphite to reduce patch fields on the surface of the metal, and is made as small as possible to allow the analysers to approach the gun as close as is feasible when non-perpendicular plane geometries are selected (see figure 2). The XY translation table is mounted from the rotating yoke, to which is attached the photomultiplier tube. This allows the gun to be dismounted from the system without the need for rewiring of the feedthrough when the need arises (filament changes, cleaning etc).
The wiring between the gun and inline socket is also shielded colour coded PTFE coated advance wire facilitating spot welding to the electrostatic lens elements of the gun. The analysers are mounted onto x-z translation tables that allow them to view the interaction region accurately over the full range of angles accessible. These lenses have a capability for energy zooming of around 10 : 1, and have a maximum entrance acceptance angle of A±3A° as defined by the entrance apertures.
This ensures that the overlap volume accepted by each analyser encompasses the interaction volume for all detection angles as the analysers move in the detection plane. These devices use an activated lead glass internal surface which has a high coefficient of secondary electron emission when a high voltage (around 3000V) is applied across the multiplier.
This noise may be picked up by the channel electron multiplier and the high voltage feed to the multiplier, and is generated internally in the vacuum system.
The CFD's are operated in NaI mode as this has a 2ms dead time following the initial pulse, thus reducing the possibility of false triggering due to any mismatching impedance reflections along the delay cable. These EHT supplies are connected via VERO 200 high voltage couplings to high voltage cable connecting to the pickoff circuitry located on the high voltage feedthroughs. This allowed the analysers to roam the detection plane over a complete 360A° angular range. The configuration of the target source hypodermic when perpendicular plane measurements are conducted. The common procedure is to initially maximise the current from the gun onto the Faraday cup, then onto analyser counts as the electron beam is moved through the gas jet. Maximising the Faraday cup current is therefore only a crude preliminary alignment of the incident electron gun beam. This therefore assumes that the analysers are initially focused onto the interaction region, and a slow iterative technique must be adopted where the analysers and electron gun are tuned so as to maximise the signal from both analysers. In this case a true differential cross section is not obtained, since the scattered and ejected electron trajectories lie in a different plane than defined in the initial experimental alignment. An EMI 9789QB reduced photocathode photomultiplier tube is installed in the vacuum system together with optical focussing and defining elements (figure 2). A group of these excited states decay back to lower valence states with the emission of visible photons at wavelengths around 450nm for both helium and argon targets.
Tuning of the electron gun to PMT counts therefore guarantees that the electron gun is steered and focussed to the point at the centre of the detection plane independent of the analysers or gas beam density.
This is mainly used when the vacuum system is baked at temperatures above 55A°C, since the photocathode is rapidly damaged by temperatures exceeding this.
The tube is a venetian blind dynode construction, and has a reduced photocathode to decrease the noise on the output of the tube to less than 20Hz.
The photomultiplier tube base was thoroughly cleaned in an ultrasound following location of these components, to displace any flux residue from the solder joints. It is therefore necessary to amplify the channeltron pulses prior to transmission to the discriminators, whereas the photomultiplier tube pulses are sufficiently large to not require further amplification. These pulses are amplified by Phillips Scientific 6954 100X amplifiers located external to the EHT feedthroughs connected by 10cm lengths of RG-58 cable.
These crates are further decoupled from the AC mains supply using filter circuitry on each supply line. Internal to these rate-meters buffer 7400 TTL chips have been added to send to 32 bit counters located in the main PC via RG-58 cable. These supplies are fully floating, their mid-point voltage being equal to the lens element voltage in which the deflectors are housed. All these supplies are fully computer controlled isolated units with low output impedance to reduce noise and eliminate current loops. This relay switching unit allows either the voltage or the current on each lens element to be measured by a Keithley Digital voltmeter.
This drive is further reduced internally by 10X reduction gears, resulting in a reduction ratio of 100:1.
This led to the ground line of the RS232 serial line moving around with respect to the 0V stepper motor reference as drive current to the motors returned along the ground line.
The optocoupler logic circuit circuit that controls the stepper motors and avoids collisions between the analysers, the electron gun, the Faraday cup and the hypodermic support.
Added to this filament supply is a computer controlled current boost circuit that can be used to increase the filament current during electron gun tuning. The additional current then returns to the 12V DC regulated supply via a second 1N4007 diode.
This therefore depends upon both the current driving the filament, as well as the resistance of the filament when hot (typically 4W - 6W). This supply feeds current to the filament without changing the characteristics of the main constant current supply used while operating the spectrometer. These high stability reference sources ensure that the analyser and electron gun positions are accurately measured with time.
A datalogger internal to the controlling PC establishes a cubic spline relationship between the measured angles and the corresponding ADC conversion from the potentiometers. This PC also controls the selection of the relay motherboard for measurement of the required lens element either in voltage or current mode when a request is sent from the controlling computer via an RS232 serial line. If it is not running, see Chapter 5.Some refrigerators are very quiet and smooth when they operate.
The spectrometer is shown configured in the perpendicular plane, the electron gun being placed in the vertical position with respect to the analysers which span the horizontal detection plane. The electron source is a heated tungsten hairpin filament heated by passing around 2A of DC current through the filament. The saturated gain of these devices yields around 1E8 electrons in the output current pulse for a single electron which enters the input cone.
This allows the analyser to roam over a complete 360 degrees of the detection plane when in this geometry (apart from the position where the analysers would clash wth each other). The analysers are then adjusted for maximum signal count and the procedure is iterated until a maximum is found. The dark noise count is also reduced when cooled, however since the reduced cathode PMT only produces dark counts of less than 20Hz at room temperature, this is not necessary during routine operations. The 1.82M resistor was chosen to optimise the single photon counting efficiency of the tube. It is not found that these solder connections significantly affect the ultimate vacuum pressure in the system.
Isolated DC supplies to these amplifiers is obtained from a standard +15V supply, the circuit diagram being given in figure 8.
The power supply to these TTL buffers is derived from the rate-meter supplies via 7805 5V regulators located internally.
This supply boosts the current without changing the main supply, thus ensuring supply stability before and after the electron gun is tuned.
The electron gun is a two stage non-energy selected gun that produces an incident electron beam current of up to 4 microamps at an incident energy from around 30eV to 300eV. The 470k resistors bias the dynodes to achieve saturation of the current pulse at the output of the tube, hence biasing the tube for single photon counting applications.
This was found to be necessary to eliminate problems associated with current loops from the 20A peak motor current feeding the common point of the logic circuitry. The analysers are identical, and consist of a 3-element electrostatic lens focussing the interaction region onto the entrance of a hemispherical electrostatic energy analyser. The Anode deflector pair corrects for any misalignment of the filament emission point with respect to the axis of the electron gun. Not MORE Perry Theories?A When Pete was at school, and throughout his teenage years, his friends and a few adults would raise their hands in alarm as Pete propounded a new theory. The Chamber is lined internally with 3mm thick mu-metal, and a mu-metal cylinder encloses the chamber externally as shown. The electrons selected in angle and energy are amplified using Mullard 919BL channel electron multipliers.
The defining apertures limit the pencil and beam angles of the electron beam following focussing by lens 2 onto the interaction region. The load is set by the 50W resistor across the anode to the HT feed, the pulse being decoupled to ground via the 1nF capacitor.
This reduces the magnetic field at the interaction region to less than 5mG, an acceptable level for the electron energies used in this experiment. The interaction region defined by the interaction of the gas target beam and the electron beam is focussed onto the photocathode of an EMI 9789QB photomultiplier tube via a lens, 450nmA±50nm optical filter and defining aperture. Placement of the apertures ensures that the beam angle is close to zero degrees at the interaction region over a wide range of energies, whereas the aperture opening reduces the pencil angle to around A±2 degrees over this energy range. Not just in The UK, but all over the World.Normally placid creatures such as foxes and squirrels have started attacking humans.
The target gas effuses from a 0.6mm ID hypodermic needle constructed from platinum iridium alloy.
The 10MW safety resistor prevents the output charging up to a high voltage if the feed is disconnected. The deflectors between the apertures correct for space and surface charge beam variations inside the field free region, whereas the final deflectors allow the beam to be steered onto the interaction region defined by focussing a 1mm aperture in front of the photomultiplier tube onto the gas target beam.
The electrons passing through the interaction region which are not scattered are collected in a Faraday cup opposite the electron gun. If you are still unsure and you own an ammeter, test the current draw of the compressor at the compressor leads. The gun, photomultiplier tube, gas hypodermic and Faraday cup all rotate on a common yoke with an axis through the centre of the horizontal detection plane, allowing all geometries from the perpendicular plane to the coplanar geometry to be accessed.
They make us obese, sluggish, and many additives are increasingly making us angry and confrontational.We are also the untidiest creatures on the planet, throwing away discarded rubbish and food.
Animals and birds are opportunists, particularly in urban areas, where Mankind has deprived them of their natural food by paving over grasslands, cutting down trees for buildings and roads, and driving out the predators natural prey such as rabbits and 'game birds'.A i»?Well then, it must also apply to BIRDS AND ANIMALS!
If the knob has an "off" setting which stops the compressor from running, it is thecold control.In the absence of an "off" setting, the easiest way to tell them apart is to pull the plastic knob off the control. Arranged installation of separate solar digital record meter as well as arrange a new digital electric consumption meter. Solar, Wind etca€¦a€¦how they manage that is a conundrum but they do invest their profits into more 'green energy' sources.My system is 10 Panels facing slightly South East and generates income of approx A?900 per year but at the earliest rate. The idea is to keep the compartment at a different temperature from the rest of the food compartment; a more optimum temperature for the particular food that you're keeping in these compartments. The rates for later installations were reduced by this "Greenest Government ever !!"By my calculations as well as generating solar electricity it will take me approx 8 to 9 years to recover the costs of materials and installation after that its free income BUT my applying for Solar is not primarily for profit but to show that clean Solar energy is possible and an inducement to othersa€¦..sadly most would rather spend their money on a Gas guzzling A?30 grand motor !! This is known as "sweating." So-called "Energy Saver" switches control small, low-wattage "mullion" heaters in the side and door panels that prevent the outside of the refrigerator from getting cool enough for sweating to occur.
Anyway back to the plot, I'm very pleased with my system, I've made a very good friend in Colin who is always ready to give advicea€¦.he even does the Band PAT Test for me ! But no probs now.I am looking at another piece of technology Colin has recommended and that is a way of diverting excess solar generated electricity to heating my domestic hot water. Air flows over it by convection; the warm air rises and is replaced by cooler air from below.
Feel for a steady flow of warm air from the drain pan side; it should be obvious (see Figure 11). It is simply a way of life to them.Not only are many houses fitted with green roofs, but so are sheds and even bus shelters! It has the veryimportantjob of directing airflow beneath the fridge, assuring that the condenser fan is drawing air over the condenser and not just sucking air in through the back of the fridge. They are sealed units and cannot be rebuilt.Replacing the condenser fan motor can be dirty and difficult.
When installing a new motor with bracket mounts, it may be easier to install the brackets loosely on the motor until you can locate the mounting screws in their holes.
Thus, when trouble-shooting the evaporator fan, you must depress the door switch(es).Open your freezer door, depress all door switches and listen for the evaporator fan.
Look first for a separate access panel or a tower within the freezer that houses the fan (Figure 14). Check for anything that may be blocking the fan, including ice from a backed-up defrost drain or a frost problem. If nothing is blocking the fan and it still does not run, check for voltage across the fan motor leads (with the door switch depressed, of course.)If you have voltage across the fan motor leads, the fan motor is bad. Itcancause ice to build up in the internal ductwork.If you hear a "whistling" or "warbling" noise emanating from the fan motor itself or from the inside of the food or freezer compartment, it is probably coming from the evaporator fan motor. They don't cost much.REPLACING THE EVAPORATOR FAN MOTORIn replacing the fan motor, you must make sure that the rotation of the new fan motor is the same as the old one.


The easiest way to do this is to look for the shading poles on the old fan motor (Figure 16).If they are on opposite corners from the ones on the new fan motor core, it is a simple enough task to reverse the new rotor in its core.
Do not remove the icemaker (if installed.)Look at and feel the panel covering the bottom or back of the freezer compartment. You will see a removable panel covering the entire back or bottom of your freezer compartment.
Make sure the power is off the refrigerator before disassembling any lighting circuit.On some bottom-evap models, you may have to remove some of the plastic moulding around the door frame to access some of the evaporator panel screws.
This can usually be accomplished by placing a pan of very hot water in various places on the panel, or by blowing warm air on it with a blow-dryer.
Therefore, when you are diagnosing a defrost problem, it's a good idea to try to avoid melting the ice encasing the terminating thermostat until you've made your diagnosis.
If the thermostat opens before you've had a chance to see if the heater works, you'll have to by-pass it. There are many styles, but most are variations of the three types pictured in Figure 20.Aback-evaporatormodel is one with the evaporator mounted vertically against theinside back wallof the freezer compartment.
These may be bottom freezer models, side-by-sides (Figure 17) or top freezer models (Figure 18.)Abottom-evaporatormodel is one with the evaporator mounted horizontally (flat) beneath a panel on thebottomof the freezer compartment (Figure 19). Does it have a fluffy (snowy) white consistency, or is it solid and clear-ish or slightly milky white-ish?Check the frostpattern.
Or is it not frosted at all?On back-evap models, examine the drain pan directly beneath the evaporator. Is it clear, or is it filled with solid ice?Each of these symptoms indicates a different problem. If you have lots of white, snowy ice, keep reading.4-5 DEFROST SYSTEMIf the frost is snowy and white in appearance, you have a defrost problem. The three main components of the defrost system are the defrost timer, the defrost heater and the terminating thermostat.4-5(a) DEFROST TIMERS AND ADAPTIVE DEFROST CONTROLIn most older refrigerators and some newer ones, a motor-driven timer (Figure 21) is used to stop the compressor and initiate a defrost cycle.
If you have a Whirlpool or Kenmore refrigerator with a flex-tray icemaker, the defrost timer is integrated into the icemaker.
This is true whether you are using the icemaker to make ice or not; it is running constantly to time your defrost cycles.
If you have a defrost problem and you have one of these machines, follow the instructions in section 4-6.Nowadays, refrigerators are being made as efficient as possible, due in no small part to government energy efficiency requirements. Defrost heaters use a lot of energy, so designers are mimimizing the total amount of time that the heater is energized. Such factors include ambient humidity and temperature, the water content and temperature of the food you put into the fridge, icemaking within the freezer, and how often the door is opened and closed.For example, if you go away on vacation for a week, the refrigerator door will obviously not be opened for a long time. Less humid air will enter the fridge than if someone was at home, and opening and closing the door. Frost buildup will be much slower than usual, so the refrigerator will not need to be defrosted as often as normal. It also will not need to be chilled as often, so compressor run times will be shorter and less frequent.Designers are using microprocessors (on solid state circuit boards) to adapt defrost intervals and durations to compensate for differences and changes in operating conditions. Such techniques are calledAdaptive Defrost Control, commonly abbreviated as ADC.To make decisions about the correct defrost duration and interval, the control board must have input about the conditions that the fridge is operating under.
Each manufacturer uses a different logic scheme and different inputs, such as door open time, compressor run time, duration of the previous defrost cycle, and duration and intervals of door openings.Door open info is provided to the logic board by the door switch - the same one that controls the refrigerator's internal lights.
For example, the ADC is programmed with a maximum amount of time that the heater can stay on; say, for 16 minutes. Often they are mounted under a cover plate or in a bracket that hides all but the advancement pinion.
The easiest way to recognize them is that the harness connection is always labelled with the compressor, defrost heater, L1 and L2.
The easiest way to see the heater is to look for the heavy, rubber-coated wires leading to it; one on each end. The element has no protective tubing and generally wraps around beneath the evaporator in a large "U" shape.You must exercise caution when handling these heaters to prevent burning yourself. If that happens, you want to turn the heater off soon after the ice melts, to prevent the evaporator compartment from heating up too much. If theterminating thermostatsenses too high a temperature in the compartment, it opens, and cuts power to the heater. The thermostat will then stay open until the compartment again reaches a very low temperature. In other words, it waits to reset itself until the cooling cycle starts again.If the evaporator is more heavily frosted, the ice may not all melt within the time allotted by the timer. The heater will stay on until thetimerstops the defrost cycle, and restarts the cooling cycle.If you initiate defrost (turn the timer on) and the heaterdoes notheat up, then usually the heater or terminating thermostat is bad. If you initiate defrost and the heaterdoesturn on, then usually the timer or ADC board is bad, and you must replace it.To diagnose which component is bad, you must initiate the defrost mode, or test continuity through the defrost heater and terminating thermostat. Within ten minutes (usually much less) you should be able to see a red glow from the defrost heater(s), which is (are) mounted beneath the evaporator.If you have an aluminum-tube heater as described in section 4-5(b), it will not glow red, but youwillsee ice melting away from its coils. Timers can get old, worn and coked up with dust, and may develop hard spots in the bearings.
If youdo nothear or see indications that the defrost heater is working, then it is necessary to investigate a little further.
If you cannot tell for sure, get the information for your model fridge from your parts man. DIAGNOSIS: DEFROST HEATER AND TERMINATING THERMOSTATIf you do not hear or see indications that the defrost heater is working, you could be looking at one of several different problems.
The heatermaybe so icebound that it would takehoursfor the heater to melt enough ice for you to see the heater begin to work. If they are not connected to a terminal block, you will need to cut the leads to test for continuity.
Make sure you're not testing continuity across the terminating thermostat too; it may be wide open above 40 or 50 degrees. With glass-tube heaters, be careful that the glass is not cracked or broken and that you do not cut yourself. It's cheap.If you have an ammeter, try to determine if the heater is drawing any power before you melt any ice. In trying to find the heater leads, be careful that you do not melt so much ice that the terminating thermostat opens.
If you suspect that the terminating thermostat might be open, temporarily bypass the terminating thermostat with an alligator jumper as described below.If you cannot find the heater leads, an alternativeis to check the current in one lead of the main power cord. Double-check this diagnosis by jumping across (shorting) the terminating thermostat with your alligator jumpers.
If the two thermostat leads are not on a terminal block, you will have to cut the leads to jump the thermostat. Remember that it's a wet environment.LIFTING THE EVAPORATORIf you have a bottom-evap model fridge, replacing the heater will involve the delicate task of lifting the evaporator up to get to the heater.
If you break or puncture one of those tubes, you're looking at a potentially expensive sealed system repair.Thaw out the evaporator as thoroughly as is humanly possible. Remove the evaporator mounting screws (if there are any) and gently lift up the end of the evaporator opposite the tubes.
Prop up the evaporator with a blunt instrument (I use my electrical pliers or a flashlight) and change the heater. Do what you went in there to do, but as much as possible, avoid moving the evaporator around too much.When you finish, gently lower the evaporator back into place. The hard tray is finished in a dark gray or black color and has rotating fingers that eject the cubes from the unit; the flex-tray has a white plastic, flexible tray that inverts and twists to eject, much the same as a manual ice cube tray would work.
The hard-tray and separate defrost timer is by far the more common arrangement.This defrost system has the same components described in the defrost system in section 4-5, except that the defrost timer is integrated into the icemaker. However, the actual switch that controls the heater is accessible.Remove the icemaker and the evaporator panel as described in section 4-4. Take the plastic cover off the face of the icemaker and remove the three screws holding the metal faceplate to the icemaker head.
Plug the icemaker back into its electrical socket and observe the drive motor in the upper lefthand corner of the icemaker head.
The defrost switch is the small, rectangular switch in the upper righthand corner of the icemaker head. Using electrical tape, tape it out of the way so it does not touch any other metal object in the icemaker head.
Using your resistance meter, you should see continuity (and no resistance) between the empty terminal (where the BLACK lead was) and the PINK terminal.You should see NO continuity between the empty (BLACK) and ORANGE terminal. When the switch toggle is depressed, continuity will be just the opposite: BLACK-ORANGE-CONTINUITY, BLACK-PINK-NO CONTINUITY. If the switch is okay, the problem is probably your defrost heater or terminating thermostat. Alignment of the gears is critical; follow the instructions that come with the gear sets carefully. If you replace the motor, you will have to re-align the defrost timing gear mechanism.RE-ASSEMBLYIf you have not removed the defrost timing gear housing from the back of the icemaker head or the motor from the front of the head, you will not need to re-align thedefrost timinggear mechanism. However, youwillneed to realign thedrivegear mechanism.Align the hole in the small drive gear with the alignment hole in the icemaker head and install the gear. If they do not line up perfectly, momentarily plug the icemaker in or apply 110 volt power to the two center leads of the plug This will turn the drive motor slightly.
Lift the spring-loaded shut-off arm (ice level sensor) as you install the cam and let it rest in the cam hollow. Carefully install the metal cover plate, making sure the end of the wire shut-off arm (ice level sensor) is in its pivot hole in the metal cover plate. Make sure the icemaker is turned on (ice level sensor arm is down) or it won't make ice.4-7 HOT GAS DEFROST PROBLEMSIf you have a refrigerator with a hot gas defrost system, the defrost mechanism is somewhat different from those described in previous sections of this book. If you suspect that you might have a hot-gas defroster but you are not sure, ask your appliance parts dealer. Most of these refrigerators were built before 1970, but not all.The main difference in a hot gas system is that there is no electrical heater or separate terminating thermostat. The defrost cycle is controlled by a defrost timer similar to the one you'll find in electric defrost systems, but the timer controls asolenoid valveinstead of aheater. These units have a temperature sensing bulb, similar to that found on the cold control (see section 4-9 and Figures 21 and 33) as a part of the timer. Its function is to sense the temperature of the evaporator so the defrost mechanism knows when to shut off.Troubleshooting a defrost problem in this system involves two steps. Wait and watch your evaporator for 10-15 minutes.If the frost starts to melt, then your defrost timer has gone bad. Thoroughly melt the rest of the frost from your evaporator and replace the defrost timer.If the frost doesnotstart to melt, then your defrost solenoid is probably bad. Fortunately, the defrost solenoid is usually designed so the electrical coil can be replaced without cutting into the sealed system. Trace the Freon tubing until you find electrical wires joining the tubing at a certain point. UNEVEN FROST PATTERNS, OR NO FROST AT ALLThe evaporator should be bitterly cold to the touch. If the evaporator is either slightly cool or not cold at all, and your compressor is runningconstantly(not short-cycling; see section 4-9) you have a more serious problem.
The same diagnosis applies if just the first coil or two in the evaporator is (are) frosted and the rest are relatively free of ice or perhaps even lukewarm.What's happening is that the Freon is not getting compressed enough in the compressor.
This could be due to two causes: either the amount of Freon in the system is low, or the compressor is worn out. Itmayonly require recharging the Freon system, which, depending on the refrigerant used, may cost you a little, or a LOT. I have only seen one exception to this diagnosis, and this is described in section 7-2.Don't let the age of the refrigerator affect your diagnosis.
Not too long ago, one of the largest appliance companies put out a series of refrigerators with compressors that were either poorly designed or poorly constructed; I never did find out which.
These were their giant, 20 to 25 cubic-foot flagship models, with techno-marvelous gadgets like digital self-diagnosis and ice and water in the door, and they were built with compressors that wore out within 2 years.Fortunately, the biggest and best companies warrant their refrigerators for five years or more, so these refrigerators were still covered under warranty.
COLD CONTROLIf your refrigerator is cold but not as cold as usual, and you cannot trace it to any of the other problems in this chapter, your cold control may be defective. To test its cut-in and cut-out temperatures, you can try putting the capillary bulb in ice water and measuring the temperature with a thermometer, but it's a wet, messy, job and it's difficult to control the temperatures.
The capillary tube is the liquid-filled temperature-sensing element of the cold control, and operates in the same manner as a thermometerbulb; in fact, the end of the capillary tube may have a bulb. The tube and bulbmaybe coiled right next to the cold control, or they may be led away to another part of the compartment.If you are justtesting(electrically) the cold control, you can jumper directly from one wire lead to the other. By doing this, you are closing the switch manually, and assuming the machine is not in the defrost mode, the compressor should start.If you arereplacingthe cold control, it will be necessary to trace where the capillary tube goes, and remove the whole tubewiththe cold control.



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