Aircon contactor and relay
This is the overview page for outdoor switching faults. A contactor or relay issue can stop startup, but we still need checks to confirm which switching point failed.
Parts summary
Warning Signs
What it is and where it sits
A contactor is an electrical switch inside the outdoor unit. It turns on power to the compressor and fan.
Think of it like a light switch. When the indoor unit signals, the contactor closes to let power flow.
A relay is a smaller switch that controls lower-power circuits and signals between parts.
Failure modes and warning signs
Contactors open and close thousands of times. The contacts wear out and stop closing properly.
You see the indoor unit running fine but the outdoor unit stays silent. Or the outdoor fan runs but the compressor does not start.
Sometimes you hear a click from the outdoor unit. That is the contactor trying to close but failing.
- Indoor fan runs but outdoor unit is silent
- Clicking sound from outdoor unit but no cooling
- Outdoor unit works some days but not others
How we verify the problem
Technicians first test the capacitor. A weak capacitor looks like a contactor fault.
They then test the contactor with power on. They check if the signal arrives and if the switch closes.
They look for burn marks or pitting on the contact surfaces. These show the switch is failing.
| Test Finding | What It Means | Next Step |
|---|---|---|
| Capacitor is weak | Weak capacitor looks like contactor failure | Replace capacitor first |
| Contactor does not close when signaled | Switch is broken | Replace contactor |
| No signal from control board | Board is not sending command | Check control board |
| Everything tests fine but nothing starts | Compressor may have issue | Check compressor |
Should you fix it now?
Replace the contactor only if testing shows it is broken. Replace the capacitor first if it is bad.
You can wait if the unit starts sometimes but not always. But do not wait long.
Do not wait if nothing starts at all. Book a technician right away to test the system.
What to expect
Contactor replacement is quick and cheap once the problem is confirmed.
Testing first avoids replacing the contactor when the capacitor is really the problem.
An intermittent contactor tends to fail completely soon, so early replacement avoids being stuck without cooling.
Common questions
Same situation with your aircon?
Describe it on WhatsApp