Question about Refrigerators
The method of starting the compressor on very old units was that a real relay would close its contacts for a few seconds shorting the connection of the start(S) post on the compressor with the run(R) post thus feeding power to the start coil in the compressor for a few seconds. Well, I guess the bright design boys/girls were told to design for less cost and eliminated the real relay altogether. In its place they made a little plastic holder that has a disc type thermistor inside it. Normal resistors have a negative temperature coeficient meaning that as temperature goes up the resistance goes down. Thermistors do the opposite so as temperature goes up the resistance also goes up. They stuck one of these little thermistor discs about the size of a penny and just about as thick between the S and R terminal posts on the compressor so that when the thermostat in the refrigerator calls for more cooling power goes to the R post and through the thermistor disc to the S (start coil) post thus energizing the start coil in the compressor and giving it the jolt it needs to get going. Since the thermistor is left connected across there it heats up from the current going through it. I measured the cold resistance of one disc at exactly 5 ohms. Using ohms law of voltage squared divided by resistance gives us for a 120 vac circuit quite a bit of power: 120 X 120/5 or around 2880 watts that might be needed to be dissipated by that little disc thermistor every time the compressor kicks on. Of course the thermistor gets really hot and its resistance goes up thus limiting the current and everyone is happy...for a while...years if you are lucky. Back in the 1960's I worked at Western Electric Co.'s Lees Summit, MO plant and was responsible for lines making thermistors including the disc type...they do a great job for the telephone company where not much current goes through them...but for high current applications such as controlling starting of refrigerator compressors the "black cookie dough" they are made of gets real hot...I mean really hot...and the dough dries out even more and finally breaks down often shorting out and leaving a black carbon mess all over everything plus the heat can cause a fire...so the old design was better as far as I am concerned using relays that often lasted 40 years with no maintenance. I digress...again... I just repaired yesterday a Kenmore side by side that was thrown away on the street...with melted run terminal post on the compressor from the blown up thermistor and it was thought by them and the service guy that the compressor was bad as well. An ohmmeter check showed indeed that all the compressor terminals were shorted to each other and to the compressor case ground. I then unbolted the compressor and gently bent the freon containing copper tubing allowing me to pull the compressor out to give good access to the terminals. I wire brushed the three terminals and around them on the compressor real good and cleaned it up using carburetor spray cleaner, allowed it to dry completely and retested with my meter and...behold...no more terminal shorts to anything and the resistance measured of the coils inside the compressor were good readings.... so... I then made a test cable which would plug into a 120 vac outlet. I then connected the 120 vac between the common(C) and run(R) compressor terminal posts while simultaneously using another wire through a push button switch to feed power also to the start (S) terminal for perhaps 2 seconds...alla kerzam...the compressor started and ran fine. I left it running for a while and found that a cup of water froze in the freezer compartment in about 1 hour. Then I installed a new thermistor unit and jerry rigged a way to make connection to the melted stub on the run(R) terminal, put the whole compressor etc. back in the unit, put the cardboard cover on and it has now been doing an excellent job of cooling ever since. You may not want to go to all this trouble...but..hey...I got a 2 year old side by side kenmore that the people said they paid over $1000 for and I only spent $22.88 on it on internet for a new start thermistor/overload module...even so, I would have preferred to use a start relay.
Posted on Aug 21, 2009
My side by fridge isn't getting cold. The freezer defrosted on me and my other side of the fridge isn't getting cold. but its still running would this be my compressor
Posted on Dec 16, 2008
My refigerator has a loud sound that has vibration and it seems like the compressor is moving and jumping up and down like its loosened off its mounts. the frig is still cold but the unit itself is bouncing up and down make terrible sounds. Help
Posted on Sep 22, 2008
If the compressor is noisy and bouncing when starting, the compressor mount inside the hermetic dome is broken. You would need to replace te compressor to resolve the problem.
Posted on Jul 21, 2010
HI. i would recommend to check the relay first, then the compressor last to confirm total failure. If both devices test out ok, this will lead to a failed main power control board.
The compressor relay starts the compressor. A fault relay can result in the compressor failing to cycle on. The relay is accessed from the lower rear of the refrigerator. The compressor relay can be accessed by removing the terminal cover box. The cover is held on by tension or with a retaining clip. On some units. the relay may not be covered at all.(each model may vary). Beneath the terminal cover(if equipped), you will find the compressor relay, and the overload protector as well. The electrical terminals of the compressor motor are located here also. Remove the compressor relay by pulling it straight off from the compressor, gently. Pull the wire off of the side terminal of the relay. It is connected with a slip on connector. Firmly pull the connector, do not pull on the wire. You may need to use a pair of needle-nose pliers. Inspect the connector and terminal for corrosion. If either is corroded they should be cleaned or replaced. There are two types of relays you may encounter, wire coil and solid state. If the relay has an exposed wound wire coil it can be tested for continuity. Otherwise, the relay is of solid state design and requires specialized equipment for testing. Test the relay with a ohm(multimeter), for continuity. Set the meter to the ohms setting X1. With the relay upside down, place the probes into the terminals labeled "S" and "M"(the labeling may vary on each model). The meter should display a reading of zero ohms, indicating continuity (or if using a continuity tester, it should light up). With the probes still in place, turn the relay over. You should hear the click of the magnetic switch engaging. The meter should now display an ohm reading of infinity (or the tester should not light up). Turn the relay upside down again, place the probe on the "S" terminal and place it on the side terminal labeled "L". The meter should now display a reading of zero ohms (continuity). Turn the relay over and the reading should change to infinity. With the relay upside down place one probe on the "L" terminal and the other probe on terminal labeled "M". The meter should display a reading of zero ohms. Turn the relay over and the reading will stay the same, zero ohms. Now, if the relay fails these described tests, it should be replaced asap.
COMPRESSOR TEST PROCEDURE
The compressor is accessed from the lower rear of the refrigerator. Generally the same proximity of the relay. The compressor motor can be accessed by removing the terminal cover box. The cover is held on by tension or with a retaining clip. The main testing points will be the actual terminal post that hold the relay, gently pull the relay of the terminal box on the side of the compressor, and use the relay holding probes for testing. Once the relay is removed, Place one probe on any terminal and then touch the other probe to each of the other two terminals. The multimeter should display a reading of zero ohms. Be sure to set your meter to 1X before beginning. Now move the first probe to a different terminal and test the other two terminals with the other probe. Finally, move the first probe to the last terminal and test each of the other terminals with the other probe. Every test should have continuity with the multimeter displaying zero ohms. If the compressor motor does not pass all of these tests, the compressor will require professional service. Now test the compressor for ground. With the multimeter still set to X1, touch one probe to bare metal on the compressor housing (it may be necessary to scratch away a little paint to expose the metal). Touch the other probe to each of the three terminals in turn. None of the terminals should have continuity; the multimeter should display a reading of infinity. If any of the grounding tests show continuity, the compressor will require professional service.
Posted on Jan 10, 2010
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