The start capacitor gives the compressor motor a burst of energy to get turning. When it fails, the compressor may hum without starting, click repeatedly, or not run at all — and the fridge warms up. It is a cheap part and a common failure, and it sits right next to the start relay you may have already replaced.
This guide covers the symptoms, the test, and the safe replacement procedure.
- Symptom: compressor hums or clicks but does not start; fridge goes warm.
- Part cost: $10–$30.
- Test: a multimeter with a capacitance range.
- Safety: discharge the capacitor before touching it — it holds a charge.
- Often replaced with: the start relay, since both fail together.
Symptoms
| Symptom | Meaning |
|---|---|
| Compressor hums, does not start | Weak or failed start capacitor |
| Clicking every few minutes | Relay or capacitor failure |
| Fridge warm, freezer warm | Compressor not running |
| Compressor hot to touch | Repeated failed start attempts |
| No sound at all | Check power and relay first |
A failed start capacitor is often accompanied by a failed start relay, because the relay switches the capacitor in and out. If you are replacing one, inspect the other.
Testing the capacitor
You need a multimeter with a capacitance range. A meter without one cannot test a capacitor directly.
- Unplug the fridge and pull it out to access the compressor compartment.
- Discharge the capacitor by shorting its terminals with an insulated screwdriver — it holds a charge even unplugged.
- Disconnect the wires and note their positions.
- Set the meter to capacitance and probe across the terminals.
- Compare the reading to the rating printed on the capacitor (e.g. 25 µF).
- Replace it if the reading is more than 10 percent off, or reads zero.
A start capacitor can hold a dangerous charge even with the fridge unplugged. Short its terminals with an insulated screwdriver before touching it, every time.
Replacing it safely
- Unplug the fridge and discharge the capacitor.
- Photograph the wiring before disconnecting anything.
- Remove the old capacitor from its bracket or clip.
- Fit the new capacitor with the same rating — capacitance and voltage must match or exceed the original.
- Reconnect the wires exactly as photographed.
- Plug in and listen for the compressor starting smoothly.
Capacitor and relay together
The start relay and start capacitor work as a pair. The relay switches the capacitor into the circuit briefly at startup, then takes it out. If the relay is stuck, it can damage the capacitor, and vice versa. Many technicians replace both at once, since the parts are cheap and the labour is the same.
| Part | Function | Typical cost |
|---|---|---|
| Start relay | Switches the capacitor in at startup | $10–$25 |
| Start capacitor | Provides the startup boost | $10–$30 |
| Run capacitor | Smooths running current | $10–$30 |
| Overload protector | Cuts power if the compressor overheats | $10–$20 |
A failed start capacitor stops the compressor starting, and the fridge goes warm. Test it with a capacitance meter, discharge it before touching, and replace it with a matching rating. Replace the start relay at the same time, since the two fail together.
Frequently asked questions
Start capacitors
Match the microfarad rating to your compressor before ordering.
