Air-con tripping the power
An air-con unit trips its breaker or safety switch — on start, when the compressor kicks in, or randomly — pointing at the compressor, an earth fault, or the supply/protection.
Safety first
An aircon tripping the safety switch may have an earth fault — a shock risk. Isolate and prove dead; don't bypass protection. Compressor/refrigeration internals need a refrigeration tech.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
Compressor or fan motor earth fault
Most likelyA motor winding faulted to earth trips the safety switch (often when that load energises).
- 2
Compressor start issue / locked rotor (overcurrent)
#2A failing compressor or start component draws excessive current on start, tripping the breaker.
- 3
Moisture / water ingress (condensate)
#3Condensate or water ingress in the unit causes earth leakage.
- 4
Protection not suited to inrush
#4The breaker curve/rating trips on legitimate start current.
- 5
Wiring/connection fault
Least likelyA damaged or loose connection in the unit/supply.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
Note when it trips (on start, when compressor engages, random) and whether it's the breaker or safety switch.
A pattern + which device (over-current vs earth-leakage).
Safety switch → earth fault path; breaker → over-current/inrush.
If random, suspect intermittent moisture/wiring.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Aircon trips power
→ step 2 - 2decision
Is unit insulation to earth good and the unit dry?
Yes→ step 3No→ step 4 - 3decision
Is the protection suitable and the compressor start healthy?
Yes→ step 5No→ step 6 - 4result
Earth fault / moisture — rectify (refrigeration tech for compressor).
- 5result
Re-examine wiring/connections.
- 6result
Compressor start fault or wrong protection — refrigeration tech / correct protection.
Common mistakes apprentices make
- Bypassing the safety switch to keep the aircon running.
- Not distinguishing earth-leakage (safety switch) from over-current (breaker) trips.
- Overlooking condensate/water ingress.
- Attempting compressor/refrigeration diagnosis without the licence.
When to stop & escalate
Earth faults and protection are licensed electrical work; compressor/refrigeration faults need a licensed refrigeration technician. Never run on defeated protection.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Split-system air-con not running at all
A split-system (head unit + outdoor condenser) is completely dead — no response from the remote/controller — pointing at supply, isolator, controller, or the indoor PCB.
Air-con runs but isn't cooling (electrical checks)
The unit runs (fan blows) but doesn't cool — from an electrical standpoint, checking whether the compressor/outdoor unit is actually being commanded and powered before handing to refrigeration.
An appliance trips the power the moment it's plugged in or switched on
Plugging in or switching on a particular appliance instantly trips the safety switch or breaker — strongly suggesting an earth fault or short in that appliance.