How to Test a Refrigerator Compressor (and What to Do If It’s Not Working)

If your refrigerator isn’t cooling but the fans and lights work, the compressor might be the culprit. Testing a refrigerator compressor takes a little caution and the right tools, but it’s straightforward once you know how. This guide explains exactly how to check your compressor and what to do next if it’s not working.

What Does the Compressor Do?

The compressor is the heart of your fridge’s cooling system. It compresses refrigerant vapor and pushes it through the condenser coils, where heat is released. From there, the refrigerant cools down, travels through the evaporator, and absorbs heat from inside the fridge. Without a working compressor, the fridge can’t keep food cold-no matter how high you crank the temperature dial.

Most refrigerators use a hermetically sealed compressor. You’ll find it at the back of the fridge, typically at the bottom, enclosed in a black metal canister. If your fridge runs constantly but never cools, or if you hear clicking or humming from this area, the compressor may be failing.

Warning: Safety First

Testing a compressor involves electricity, so unplug the refrigerator before you start. Never work on a fridge while it’s plugged in. If you need to take live voltage readings (rarely necessary for home users), only do so if you have experience and the right safety equipment.

Many compressors also contain refrigerant under high pressure. Never try to open the sealed compressor canister or puncture any lines. If you suspect a refrigerant leak, call a licensed technician. For basic electrical tests, though, you can proceed with standard hand tools and a multimeter.

Tools and Parts You’ll Need

• Digital multimeter (with resistance/ohms setting)
• Needle-nose pliers
• Flathead screwdriver
• Work gloves
• Optional: Replacement start relay/overload protector if needed

A clamp meter is useful if you want to check compressor amperage later, but most homeowners won’t need to go that far. Make sure your multimeter has good batteries and can measure low resistance accurately (down to a few ohms).

Accessing the Compressor

Move the fridge away from the wall and unplug it. The compressor is almost always at the back, under a metal or cardboard panel near the floor. Remove the panel with a screwdriver to expose the compressor and its wiring.

You’ll see a black cylindrical canister with a small box attached to one side. The box contains the start relay and overload protector, which are plugged into the compressor’s terminals. Carefully disconnect the wires and gently pull off the relay assembly. Take a photo first so you can reassemble everything in the correct order.

How to Test Compressor Terminals with a Multimeter

With the relay removed, you’ll see three metal pins arranged in a triangle. These are the common (C), start (S), and run (R) terminals. They let you test the internal windings for continuity and shorts.

1. Set the multimeter to measure resistance (ohms, Ω).
2. Test between pins: Place one probe on each pair of terminals: C-R, C-S, and R-S. Typical readings are:
   • C-R: 1-5 ohms (run winding)
   • C-S: 3-12 ohms (start winding)
   • R-S: Should equal the sum of the other two readings
3. Check for shorts: Place one probe on each terminal and the other on the compressor’s metal casing. The meter should read OL (open loop) or infinite resistance. Any resistance here means a shorted winding and a bad compressor.

If your readings are way off, or you find a short to ground, the compressor is bad. If they’re within range and the windings aren’t shorted, the compressor is probably OK electrically.

What If the Compressor Passes the Test?

If the windings all test good, the compressor may not be getting the right power. The most common culprit is the start relay or overload protector (the small plastic box you removed earlier). If you hear a clicking noise every few minutes, the relay may be failing to start the compressor.

You can test the relay for continuity or try swapping it with a known-good replacement. Some hardware stores carry universal refrigerator start relays, or you can order one using your fridge’s model number. If a new relay fixes the problem, you’re in luck-the compressor itself is fine. If not, and the compressor won’t run when directly powered (see below), it’s probably failed internally.

Signs Your Compressor Has Failed

A failed compressor often shows some clear symptoms. The most obvious sign: the fridge runs but never gets cold. You might also notice:

• Loud clicking, buzzing, or humming from the compressor area
• Compressor is hot to the touch but not vibrating or running
• Repeated tripping of the overload protector
• Electrical burning smell or visible scorch marks

If your compressor passes the ohms test but still won’t start with a new relay, the internal piston may be seized, or there could be a refrigerant problem. Either way, replacement is usually required. Compressors are not user-repairable parts.

What to Do If the Compressor Isn’t Working

If your compressor fails the continuity test or is shorted to ground, it needs to be replaced. This is not a DIY repair for most people. Compressor replacement involves recovering refrigerant, special tools, and welding copper lines. A certified appliance technician or HVAC professional must handle this job.

Weigh the cost of a new compressor against the price of a new fridge. On older models, replacing the whole refrigerator often makes more sense. If your fridge is under warranty (many compressors have longer coverage), check with the manufacturer before you pay for any repairs.

Frequently asked questions