How to Test A Domestic Refrigeration Compressor

Some Basics First

• These tests are not for a capacitance Start Compressor :See the Commercial Refrigeration Compressor Section to test this type of compressor

• Unplug the refrigerator or turn off the breaker that powers it. Since you will have to get to the backside of the refrigerator anyway, I would recommend you unplug it

• At the bottom rear of the refrigerator you will see the compressor. On the side you should see the terminal box with wires coming out of it. Remove the cover from this box. The cover will be held in place by either screws or retaining clips.

• With the cover off, you should see the Start relay, the overload protector (Clixton) and the terminals for the compressor motor. The Start relay can be removed simply by pulling it straight off of the compressor. inspect or any signs of Corrosion or heat damage

• Use the long-nose pliers to pull the wire connector off of the relay. Pull it off by gripping the connector, NOT the wire. Inspect both the connector and the relay for any signs of corrosion. If there are any, then you should replace the part.

• Use the long-nose pliers to pull the wire connector off of the relay. Pull it off by gripping the connector, NOT the wire. Inspect both the connector and the relay for any signs of corrosion or heat damage. If there are any, then you should replace.

• There are a number of test that you can perform to check if the Refrigeration compressor in faulty

Winding Burnt to Earth

• Set your Multimeter to Max Ohms reading(You know, the one that wants to read if you just touch the Probe terminals) or Meggar to 500v .Touch one of the tester's probes to Earth or a copper pipe and leave it there. (Test the meter to make sure its set correctly) Then, use the other probe to touch first one then the other terminals and finally the last one.

• The tester should display a reading of "zero" ohms or Clear reading for each test. The compressor is in Order

• Any reading here indicates that the wiring is no longer insulated and touching earth. The compressor has to be failed

• Winding Burnt Between Coils / Windings

• On the Compressor you will see three terminal points randomly number them a,b,c or 1,2,3, or left, right, top, Whatever......

• Set your Multimeter to read Ohms reading or set your Meggar to Ohms . (Test the meter to make sure its set correctly) Then, Set one probe to touch first one "a" or "1" or whatever Now leaving this probe on this terminal take the other probe and Test:

  • Ohm reading "a" to "b" = record reading a-b

  • Ohm Reading "a" to "c" = record reading a-c

  • NOW MOVE the Fixed probe to the Next terminal Say "b"

  • Ohm reading "b" to "c" = record reading b-c
  • You now have three Ohm readings
  • a-b =

  • a-c =

  • b-c =

• Now some Rules
• The highest reading MUST be equal to the other two reading ADDED together

• The highest reading is a reference to two terminal (Say "b-c") the terminal that is not mentioned in this reference (this case "a") is the Common or the terminal that you connect the Clixton or Overload to

• The Second highest Ohm reading is the Run terminal

• The lowest Ohm Reading is the Start Terminal

• Conclusions
• If the Reading DO NOT balance then the windings are burnt between coils and compressor has to be failed

• The reading must all be in the same ball park say 4.5.9 (4+5=9) or 12, 15, 27 (12+15=27) if not then the compressor is giving false reading and must be failed.

If you really clever and are sure of your Common, Start and Run terminals, you can try start the compressor manually by Connecting a Neutral to the common terminal, a jumper between Run and Start. Put power on then as the refrigeration compressor then as the compressor labours, remove the jumper leaving Line/Live on run and neutral on Common, the compressor should run very comfortably (Keep a close watch on your AMPS)

Compressor Seized

• If you have done all the above tests and the compressor Passes, and still find that the Refrigeration Compressor Amps (Current) is to high or the compressor will not rotate then in all likelihood the compressor is seized or failing mechanically, her are the logical symptoms
• Refrigeration Compressor runs for a short while before the clixton overload switched the compressor off, The compressor starts up after a short while and the cycle is repeated On /OFF (Short cycling)

• The Refrigeration Compressor merely hums and does not run

• The compressor runs drawing abnormally high current (Amps)

To Test Refigeration Compressor valves Inefficient

• To test Refrigeration Compressor Suction Valves

• Disconnect all pipework from the Hi-side / Discharge pipe of the Refrigeration Compressor

• Connect your Refrigeration Gauge Low side Gauge to the Suction /Low-side of the compressor

• Open all Valves on your Refrigeration Gauges

• Start the refrigeration compressor

• Close the Low side Valve on your Gauge and observe to what level of vacuum the Refrigeration Compressor pulls the Gauge.

• A good compressor will pull the Gauges into a deep Vacuum , A Faulty Compressor will hardly be able to Draw a vacuum or even just get the Gauge down to Zero

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• To test Refrigeration Compressor Delivery / Hi Side / Discharge Valves

Be Very Careful in Performing this Test. Major injury and/ or Damage to equipment can Occur

• Disconnect all Pipework from the Suction / Low -side of the compressor

• Connect the HIGH SIDE GAUGE of your Refrigeration Gauges to the Hi Side / Discharge Side of the compressor

• OPEN all Valves on your Refrigeration Gauges

• Start the compressor

• GENTLY close you Refrigeration gauge Valve to throttle the Delivery of the compressor WATCH the Gauge slowly climb as you slowly throttle the delivery

• A good Compressor Discharge Valves will very quickly MAX you Gauge out.

• A Refrigeration Compressor with burnt / bent or leaky valves will struggle to get the High side gauge to go to its Maximum reading