Quick answer Test in this order: start relay (cheapest, most common failure), then the run capacitor, then the compressor windings for resistance and continuity to ground. If the windings read open or shorted to ground, the compressor is bad. If they read normal, the fault is almost always the relay or capacitor.

When a refrigerator stops cooling and the compressor is silent, the instinct is to assume the worst. But the compressor is usually the last thing to fail — the start relay and run capacitor are far more common culprits, and they cost a fraction as much to replace.

This guide walks through the tests in the order a technician works: cheapest and most likely first, compressor last. You will need a multimeter with a continuity and resistance setting, and about an hour.

On this page

  1. Safety first
  2. 1. Test the start relay
  3. 2. Test the run capacitor
  4. 3. Test the compressor windings
  5. Reading the results
  6. FAQ

Safety first

Unplug it Always unplug the refrigerator before removing any panel or touching any terminal. The compressor circuit runs on mains voltage and the capacitor can hold a charge even after power is removed.
  • Unplug the refrigerator and wait five minutes.
  • Discharge the capacitor safely before touching it (see below).
  • Work on a dry surface with dry hands.
  • If you are not confident working around mains voltage, stop and call a technician.

1. Test the start relay

The start relay sits on the side of the compressor and gives it the initial jolt it needs to start. It is the single most common failure in a “compressor won’t run” diagnosis, and it is cheap to replace.

  1. Unplug the fridge and pull the relay off the compressor terminals.
  2. Shake it next to your ear. A rattle means the internal contacts have broken — replace it.
  3. Set the multimeter to continuity. On a PTC relay, the two main terminals should show continuity.
  4. No continuity, or a rattle, means the relay is bad.

If the relay rattles or reads open, replace it before testing anything else. A new relay is inexpensive and often fixes the problem outright.

2. Test the run capacitor

The run capacitor helps the compressor motor run smoothly. A failed capacitor can stop the compressor starting, or make it hum and trip the overload.

  1. Discharge the capacitor by bridging its terminals with an insulated screwdriver (you may see a small spark — that is the stored charge).
  2. Set the multimeter to resistance (the highest range).
  3. Touch the probes to the terminals. The reading should climb as the capacitor charges.
  4. Reverse the probes. The reading should climb again in the other direction.

A capacitor that reads zero, reads open, or does not climb is failed. A quick functional check is to set the meter to continuity with the beeper on: touch the probes for a few seconds, then swap them — a short beep means it is storing some charge. That confirms it works but not that the capacitance is correct, so replace it if in doubt.

3. Test the compressor windings

Only now do you test the compressor itself. The compressor has three terminals — commonly labelled C (common), S (start) and R (run). You are checking two things: that the windings have resistance, and that none of them is shorted to the metal body.

  1. Set the multimeter to the lowest resistance range.
  2. Measure between C and S, C and R, and S and R. Each pair should show a low but non-zero resistance.
  3. The two smaller readings should add up to roughly the largest one (C–S plus C–R ≈ S–R).
  4. Now set the meter to continuity and touch one probe to a terminal and the other to the bare metal compressor body. There should be no continuity.
What the readings mean Open (infinite) resistance on any winding means a broken winding. Continuity from a terminal to the compressor body means the winding is shorted to ground. Either one means the compressor has failed and needs replacing.

Reading the results

TestGood resultBad resultAction
Start relayContinuity, no rattleRattle or openReplace relay
Run capacitorReading climbs both waysZero, open, no climbReplace capacitor
Windings C–S, C–RLow, non-zero resistanceOpen (infinite)Compressor failed
Terminal to bodyNo continuityContinuityCompressor failed

If the relay and capacitor test good and the windings read normal, the compressor is probably fine and the fault is elsewhere — a thermistor, the control board or the defrost system. If the windings are open or shorted, the compressor is the problem and replacement is usually not economical on a domestic fridge.

When to call a technician instead

Testing the relay, capacitor and windings is within reach for most people. But there are points where the sensible move is to stop and call someone.

  • The windings read open or shorted. Replacing a compressor needs refrigerant recovery and recharge equipment, which is regulated in most countries. On a domestic fridge it is rarely economical.
  • You are not comfortable with mains voltage. The compressor circuit runs on mains power and the capacitor holds a charge. If that makes you uneasy, stop.
  • The fault is intermittent. If the fridge works sometimes and not others, the diagnosis needs more than a static test — a technician can watch it under load.
  • You have already replaced the relay and capacitor. If a new relay and capacitor did not fix it, the problem is deeper and the next step is a professional.

There is no shame in stopping. The value of these tests is that they tell you whether the repair is worth doing at all — and often the answer is that a cheap relay fixes it, or that the fridge has reached the end of its life.

Tools for this job

You need a multimeter with a resistance range, and a start relay and capacitor if the test shows they have failed.

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Frequently asked questions

How do I know if my refrigerator compressor is bad?
Test the windings with a multimeter. Open (infinite) resistance on any winding, or continuity between a terminal and the compressor body, means the compressor has failed. If the windings read normal, the fault is more likely the start relay or run capacitor.
What is the most common reason a compressor won't start?
A failed start relay. It is the cheapest part in the circuit and the most common failure. Shake it — a rattle means the internal contacts have broken and it needs replacing.
Can I replace a refrigerator compressor myself?
Technically possible but rarely worth it. It requires refrigerant recovery and recharge equipment, which is regulated in most countries. On a domestic refrigerator, the cost usually exceeds the value of the appliance.
What resistance should compressor windings read?
It varies by model, but typically a few ohms to a few tens of ohms. The key checks are that none reads open (infinite) and that the two smaller readings roughly add up to the largest. Always check for continuity to ground as well.
Is it safe to test a refrigerator compressor with a multimeter?
Yes, if the refrigerator is unplugged and the capacitor is discharged first. The capacitor can hold a charge after power is removed. If you are not comfortable working around mains voltage, call a technician.
Bottom line Test the start relay first, then the run capacitor, then the compressor windings. Most “dead compressor” diagnoses turn out to be a cheap relay or capacitor. Only if the windings read open or shorted to ground is the compressor itself the problem.
A

Apartment Air Fix Editorial Team

We test and write about the appliances that break in apartments. Our recommendations are based on hands-on use, manufacturer specs and verified owner reviews — never on commission rates.

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