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Replacing compresor start devices
To begin, if you are replacing the start device with the original factory part,or a substitute that is a direct plug in, and the old device simply blew open you will probably not need any meter.Just make sure you take a picture of the old device, or make a diagram of which wires go where. Also, you can disregard reading the rest of this article. With the exact device, you just stick it in and wire it per the old one. If you are replacing a discrete klixon (A narrow, white item) and the PTCR relay( a small, black item), it's impossible to plug in the new PTC device wrong, but you could wire it up wrong, just note which wires went were, or take a picture of it. It is worth noting, these devices rarely fail unless there is a burnt wire there, or a shorted compressor, or a cheap after market one.To prevent wiring errors and if the start device is a discrete ptcr device ( a small black item), or a white box it is vital to test the old device. If a white box, use an ohmeter and measure which device input pin is zero ohms between it and one of the output pins that plug into the compressor.That is the compressor run pin!! If a black ptcr do the same thing.Hint**: If you have no ohmeter and your start device is a white box, pry it apart with a screwdriver. You will see a metal strip that goes directly from the front spade terminal to one of the compressor terminals. Virtually 100% of the time that is the run terminal of the compressor!!
If you are using a universal replacement, and you fail to check the compressor with a meter,and you wire it up wrong, you could blow out the start winding! The klixon might prevent this,but I would not take that chance. You will not have a klixon if you are using the URO41 (AP4503418) (a universal start device) and if you wire it up wrong, there is virtually a 100% chance you will blow out the start winding, usually within a few seconds and even if you measure high,continuous start current, you may not have time to unplug the fridg before the winding blows open!A typical TI klixon takes about 2-3 seconds to trip open.That is sufficient time for the current to exceed the fusing rating of the start winding, or damage it. Refer to the section below to identify compressor pins. This item will not provide over temperature/ power surge protection, so I do not recommend it unless you have no other choice.Refer to the paragraph below for compressor pin identification.
If your compressor fails to start, you may just need a new start device.If your compressor hums, then clicks off repeatedly, unplug it to avoid compressor hard start failure! Warning, if the lights dim, or the compressor hum is really loud and very hot, you may have a shorted compressor winding, or a grounded winding! Just check with a meter. In this case, a new start device will not work and if you use a start device that has no klixon,but a thermal cutout, it might catch on fire!
If ok, verify your compressor is getting 115 volts.Check with the compressor plugged in to avoid false readings.
If ok, next measure the inrush starting current with an amprobe. If 15 amp or less(assuming the compressor horsepower is less than 1/3, most are), then you may be able to fix it with a new start device, if the old device rattles when shaken or is just blown open. Just order the factory replacement device and NOT a substitute (unless not available) and install it by removing the compressor side cover and prying off the device.The new device may look a little different than the old one, but it is electrically equivalent.The wires to it are not polarity sensitive. If the overload klixon ( a thin, plastic device) and start relay ( a black, plastic part) are separate items, just remove and replace both. Just make sure the run capacitor (if your fridge has one) is wired between the run and start compressor pins, no change to the refrigerator wiring will ensure this, just verify. This capacitor ads running torque to the compressor and helps to avoid compressor stall during low line conditions.Normal run current now should be less than 2 amps.It is important to measure run current. If well over 2 amp you run the risk of the start device burning open, and possibly starting a fire if you are not using a protective klixon. If the compressor now fails after a short period of running, it has seized up due to varnish buildup or a burnt winding. and may not be repairable.They do sell a compressor additive, Supco 88 that will dissolve varnish, but it must be installed by a pro.
If the compressor fails to start with the new device and the compressor is a R134A refrigerant type (less than 1/4 hp, about 1.2-1.6 amp), your compressor may NOT be fixable,your start/run windings are burnt or the compressor has seized, possibly due to varnish buildup.
The use of a universal 3n1 hard start kit for this type compressor is NOT recommended; this "fragile" type compressor start winding will burn out from the high inrush current and if your fridge has an adaptive defrost board the high inrush current will eventually blow out the board. Also, if the compressor seizes, or starts to draw high current ( I have measured 15 amp) the 3 n 1 units will overheat and possibly cause a fire! Sound engineering analysis supporting this is covered in a separate report. Simply put, these devices allow peak power surges exceeding 3000Watt!! and rapidly, interrupted power levels will exceed 3000watts RMS. I have seen compressor windings explode and short to the motor housing!
A lot of the older refrigerators like the old GE's with the hot dog shaped compressors can safely function with a 3n1 hard start kit, so for these it's safe to use, just check the name plate for total current draw, if above say 2.5 amp it's ok. These older compressor motors are designed with power surge impedance protection and will not fail due to miss wiring, or severe power surges.
If you want to use a universal start device like the URO41 be aware this device will not thermally protect the compressor and will allow higher power surge inrush current than the original klixon, thus it will lead to eventual compressor burnout, just not as fast! It comes with run capacitor wires and you will need to properly identify which compressor terminals are common, start and run to properly connect it.To keep the same safe overload protection, use the original klixon. When I replace start devices, I triple check for proper installation and confirm by checking the wiring of the old device. So far, after 15 years, I never blew a compressor out, except once when I used a 3 n 1 unit.
If you own and can use a meter, the following repair method is preferred and is considerably cheaper!
The PRIME compressor burnout protection device is the original klixon overload device, a thin device attached to the common compressor terminal. Most of the time it is buried in the start device box, just pry it out. This device provides very good thermal overload and power protection and rapidly opens from over current conditions like line surges and stays open for a period of time to allow the windings to cool down.This device is very reliable. If this is ok, it should measure nearly zero ohms. You can retain this, and just replace the start relay with a GE PTC device, a WR07X10051, or WR07X10055, (AP3414961, AP3772916),depending on the compressor run current.The first one, for current draw over 1.5 amps, the next one for current draw less than 1.5 amp. The mating klixon is WR8X122 (AP2061490)These currents have been arbitrarily selected, and not set in stone. Usually they plug right into the compressor start and run pins, but it is best to check with a meter, that the device is installed properly. If you mistakenly wire the start pin directly to the fridg power wire, you will rapidly burn out the start winding in the compressor before the klxon trips off. If you hold the device with the protrusion on top and the round compressor terminals on the back, the run spade terminal is on the right side. Just verify with a ohm meter that the left side spade terminal is shorted to the left side compressor terminal. The right side spade terminal will show 5 - 10 ohms resistance to the left side compressor terminal. On the back of the ptcr, the left compressor run terminal is 6, the start 5. Sooo.. if you put one refrigerator wire on the right spade terminal and the other one on the klixon, you should be ok. These devices rarely burn out due to their superior thermal construction. This will give good compressor protection. Just be SURE you wire in the original run capacitor if the fridge. has one,failure to do so will ensure eventual compressor failure. This capacitor is always located near the compressor.
Also, when checking the compressor terminals, the start winding, has the higher resistance when measured from the common pin, the run winding, less resistance.The common pin is usually on top where the original klixon unit was.*** On some newer compressors, it's hard to tell which terminal is the start terminal and sometimes the common terminal is on the bottom. Then you must check the old start device. The pin that was wired directly to the compressor terminal through the old start device is the run terminal. If the start device is badly burned, you should refer to fridg's schematic to find the run pin wire. Most of the time, the compressor common wire is white and the run wire is blue or black. However, in every really destroyed device, I was always able to trace the exploded wafer terminal back to the compressor start pin. In some cases, the start device burns so bad, it ark welds metal to the start pin. In this case, you will need a dremel grinder to clean up the pin
One word of caution, if you use a non-factory authorized start device, it will void your compressor warranty.
** If your compressor is hard starting, it may be possible to fix it.
Measure the original start device resistance. It may be inside a large, white box, or a small,black plastic item plugged into the run and start pins. If it's around 7.5 ohm cold,or higher, replace it with a GE part WR07X10051 which measures around 5 ohm cold. This will increase the starting torque about 33%, probably will reliably start compressors with "mild" starting problems. Worth a try. Most of these hard starting compressors just have a damaged/partially shorted start winding. Best to add a 1000 joule surge protector to the wall outlet to prevent further damage.
I recently fixed a compressor in this way with no callback. The fix does not increase power consumption and is completely safe. Presently, compressors at start up, routinely survive 100% increase in starting current during power surges, 33% increase is small in comparison.
A surge protector is recommended if this fix is implemented. *** The best surge protector is the Belkin F9H100-CW $ 6.99, available at Amazon.com This unit will not blow open from a power surge and has ground integrity check and surge protection status led's.
To install discrete klixon (a thin,white item) and the black plastic start device, first identify the compressor pins. The common pin is usually on the top, other pins under that will be side by side. Measure the resistance from the top pin, to each bottom pin. If one pin (usually on the right) is a higher resistance than the other pin, that is your start pin, the other the run pin. resistance between these bottom pins must equal the sum of the two measurements.If these measurements are nearly the same, you must verify from the old start device which fridg wire went directly to which pin, that is the run pin. In my repairs, even if the old start device is a charred, smoking mess, you can always trace the wire that went from the external pin directly to the run pin.
Plug in the klixon in the top pin. Then hold the start device with the tab on top and the spade terminals facing you.Measure resistance from the left spade terminal to the other side left terminal that plugs in the compressor, should be zero ohms. From that terminal to the right compressor terminal, resistance must be between 5 and 10 ohms.
If ok, plug the PTC relay into the compressor bottom terminals. The refrigerator power white wire gets plugged in the klixon, the other into the left terminal of the start device. The run capacitor gets wired between the two opposite spade terminals on the PTC relay. Before you plug in the fridg, verify from the old start device that the fridg wire went directly to the run terminal on the left. Hope this is clear enough.
(The following verification procedure will guarantee safe compressor operation)
Before plugging in, verify proper installation. Measure the start winding and run winding resistance before you install parts and record. You will need an accurate digital meter for this. Once the parts are installed, Measure the resistance from the PTC relay spade terminal you believe is the start terminal, to the common terminal, should be exactly what you measured for the start winding before. Now measure the other PTC relay spade terminal, should be the parallel combination of the run winding and the total series resistance of the start device and run winding. For example, if you measured 8 ohms for the start winding and 6 ohms for the run winding, you should read about 2.4 ohms. This also assumes you measured about 3 ohms for the run winding and 5 ohms for the PTC. Formula for parallel resistance is 1/(1/R1+1/R2)
** There is an alternate device, a UPRO41 (AP4503412) that is safe to use in 90% of compressors! It just has the same problems as the URO41 and not recommended unless you have no other choice. It just plugs right in, no meter needed. Designed to operate on 1/4- 1/3 hp compressors. It also comes with wiring info! If the compressor terminal common is on the top or bottom, it will work. The device has the ptc internal start wafer wired to the bottom right compressor pin, (upper left if the compressor pins are upside down with the common pin on the bottom). Best to verify run and start pins first. Some oddball compressors are wired with the start pin to the left (rather rare) and the URO41 cannot be used.
Sorry this is so complicated, but apparently all start devices are not identical in wiring and all compressors do not have the start winding pin on the bottom, right. This complicates things.
** Sorry for past errors in this report, everything is now corrected and safe to use. This report has not been reviewed by another electrical engineer in this field, so I welcome any comments/corrections by a competent engineer. Come Spring, I will search for a R134A compressor (they are hard to find) to do more measurements, so some changes/additions may happen at that time.
*** For pro. tech's and persons with a meter, I would advise to never use a boxed ptcr and overload combo. All the units I have seen use a poorly heat sinked start waifer. In a lot of cases, the waifer acts as a fuse and blows open. Also, some manufacturers use a thermal overload that is thermally activated and not a klixon which is high current activated. Failure to use a klixon will allow very high peak overload currents that may damage the compressor under worst case situations.In addition, these thermally activated overloads can get extremely hot if the compressor draws high current and can cause a fire!
Use of the correct discrete ptcr (make sure it is a well heat sunk device like the GE one) and the original klixon is recommended.
*** New compressor and part test results. Compressor tested, Samsung .13 HP with 10 amp trip point klixon. Overview; objective to determine length of time to start winding failure. The high flux levels in the iron core at start up( from the high start winding current) drive the inductive reactance of the winding down toward zero intentionally (by design) to provide high starting motor toque. Failure to control the time and level of this current will result in winding fusing open.)
Using a portable scope, the following data was collected using short time pulse testing with long delays to allow ptc device and windings to cool down. Pulse duration aproximately 1/2 second.
Common ( for most full size refrigerator compressors) klixon dropout current 20 amp, 1/5 hp dropout ( for small refrigerator compressors) 10 amp; takes 2- 3 seconds for dropout dependent on level of current. The dropout current for the URO41 and the 3 n 1 hard start is higher than 26 amp which is correct to allow use on the higher hp compressors it was designed to work on!! This is way above the manufacturers recomondation. This confirms need to retain the original klixon to provide overload protection of 20 amps max.
High current (saturated core) start winding reactance around +J2 ohms,copper resistance, 4 ohm, vector sum 5 ohms, locked rotor current about 20 amps ( with no external resistance)real power dissipation about 1200 watts, time to fuse open unknown, not willing to destructive test.
The transient response was not visible due to the scope inability to trigger on a complex waveform. Normal start current with ptc device, 12 amp peak, compressor start up time around .2 second.
Tested a common 1/5 HP GE compressor, results completely different.
Locked rotor start winding current around 7 amp, real power dissipation about 200 watts. For windings under oil, probably a safe level.
*** Conclusion: Determined the use of a Hard start kit will lead to compressor failures due to greatly increased transient response due to the start capacitor producing uncontrolled inrush currents during power surges.To calculate the transient response is very difficult without iron core permeability data vs flux level chart and air gap data. The peak power level can be estimated during peak voltage levels of 240 volts (typical double line voltage a power line transformer will put out) for a 3 ohm run winding is 19.2 k watt peak! This assumes near zero inductive reactance due to the very high current levels and 2 mill.second periods and you are close to the power line transformer. If there is substation contactor chatter, the rms value will cetainly fuse the winding open.
If the start winding is energized directly from line voltage, expect winding failure within 2 seconds, well before klixon tripout.This has been verified when a customer wired the compressor start winding directly to the line voltage. The "normal" start current with a 5 ohm ptc device is around 14 amps for less than 100 milliseconds due to the very rapid increase of ptc resistance as it is consuming 980 watts peak. Just like the klixon, the ptc will retain a very high resistance for several seconds till it cools down.
Data shows the dramatic lowering of the compressor impeadence from J115 ohms to J2 (data is a bit in error as there is back emf generated by compressor) Locked rotor test is impossible as the motor is not accessable.
Per the common compressor manufacture recomendations that use a 20 amp klixon, universal start devices like the URO41 far exceed their recomendations and will lead to compressor failure during power surge conditions.
Use of a surge protector is advised as the high voltage spikes can do a lot of damage. Recomend the Belkin F9H100-CW $6.99 at Amazon. Has ground integrity and surge protection integrity indicators.
*** After searching for months, I found a good universal start device for the new compressors with the start winding pin on the lower left.. AP3796513, WR09X10106 $20, internal 20 amp klixon, 5 ohm ptc device in a nice neat package as a direct plug in!! And it is impossable to wire it wrong!!!
Start current comparison of R12 compressors and R134A compressors.
The R12 compressors have, in general 3x the hp as the new ones, thus the starting current is much smaller and the core saturated reactance is much larger.
The new R134A compressors, to save energy and still provide the same starting torque into the same equalized pressure load, must have a much larger starting current. Thus, the new compressors easily fail during a power surge when the rms value exceeds the fusing current limit.
Virtually, 99% of the time, the fast acting ptcr device and klixon effectively limit the overload current during power surges. These are carefully selected by the manufacturer, and substitution is not recommended.
For the packaged ptcr device located further from the compressor in a box, it usually burns out during a power surge and thus saves the compressor.
Using any inferior start device or overload will guarantee eventual compressor failure during a power surge.
It has been my experience, the best ptcr device is the GE WR07X10051 series and the best klixon is the GE WR8X 122. These devices are cheaper than most boxed devices, but you must wire in the run capacitor and carefully verify the run and start terminals of the compressor. If the start compressor pin is on the bottom, left, or upper, right they are safe to use.
Last edited by richappy : 09-02-2013 at 10:07 AM.
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