An AC compressor not working is the classic reason an AC runs but gives warm air. The compressor sits in the outdoor unit of a split AC, or in the rear of a window AC, and it squeezes refrigerant so the system can move heat out of the room. When it stops, the fans may still run, but the cooling stops.
Not every warm air case is the compressor itself. A tripped overload, a dead capacitor, a stopped outdoor fan or low voltage can stop it from starting while the compressor is healthy. You can safely check a few things from the outside, but testing, repairs and gas work are for a trained technician. Never open the outdoor unit. If a brand code is also showing, look it up through the AC error codes hub.
Common causes
1Low or unstable voltage
How to tellCompressor tries to start and trips, lights dim, worse in the evening
What fixes itElectrician measures the supply and the stabiliser rating
2Failed start or run capacitor
How to tellOutdoor unit hums but the fan and compressor do not start
What fixes itTechnician tests and replaces the capacitor
3Outdoor fan stopped, unit overheated
How to tellCooling stops after a few minutes, outdoor unit feels very hot
What fixes itTechnician checks the fan motor; clear space around the unit
4Overload protector or thermal cutoff tripped
How to tellCompressor stops and restarts after a long gap
What fixes itSwitch off for 30 minutes; if repeated, technician
5Low refrigerant or a blocked system
How to tellCooling faded over weeks, frost on pipes, then nothing
What fixes itLeak tracing, repair and a recharge by a technician; no home gas work
6Seized or burnt compressor, or control board fault
How to tellLoud click, burning smell, or no sound at all and no sign of power
What fixes itAuthorised service tests the unit and quotes the repair
How to fix it, step by step
Check that the AC is in cool mode
Set cool, 24 degrees and fan on auto. If the AC is in dry or fan mode, the compressor may not run. Replace the remote batteries as well.
Listen for the outdoor unit waking up
Give it about three minutes. The outdoor fan should spin and a low hum should begin. Watch from a safe spot. If nothing happens, or you hear humming followed by clicks, switch the AC off and remember what you heard.
Check the supply and switches
Confirm the MCB and the outdoor isolator are on and that the stabiliser light is normal. If the MCB trips each time, leave it off and call service.
Wash the indoor filters
Dirty filters raise the load and can cause protective stops. Clean and dry them, then restart. This will not fix a failed compressor but removes a common contributor.
Clear space around the outdoor unit
Remove loose leaves, covers or stored items that block the grille. Keep at least a hand width of free space on the sides. Do not touch the fan or inside the unit.
Give a hot unit time to rest
Switch off completely for 30 minutes if the unit was running hot in the sun. Protectors can reset themselves. Restart once.
Stop and book a technician
Hums without starting, clicks, burning smell, repeated tripping or ice with warm air all mean stop. Repeated tries can burn the windings and cost more.
Split AC compressor not working but fan is running
In a split AC, two fans can run: the indoor blower and the outdoor fan. If only the indoor blower runs, the outdoor unit is not powered, has lost the communication link, or has a failed capacitor or protection. If the outdoor fan runs but the air is warm, the compressor itself, the refrigerant circuit or a valve may be at fault.
You hear the outdoor unit start, the fan spins, but there is no deep running sound, and the room does not cool. That points to the compressor not running while the fan is, so the likely suspects are the capacitor, the overload protector or the compressor. Only a technician can tell which. In short, why the compressor is not working in an AC is a question for gauges and a meter, not for guessing.
Signs that the compressor has a problem
| What you notice | Usual suspect |
|---|---|
| Outdoor unit completely silent | No power, link fault, or board |
| Hum then click, repeat | Capacitor, low voltage or a stuck compressor |
| Fan runs, no deep sound | Compressor or overload not running |
| Runs, then stops when hot | Overheating or protector |
| Burning smell | Switch off and call service at once |
AC outdoor unit and outdoor fan not working
If the outdoor fan is not turning, the compressor will soon overheat and stop. A split AC outdoor unit fan not working has several possible causes. A stopped fan can come from a failed capacitor, a worn motor, a seized blade, or a board fault. Do not try to spin the blades or open the grille, even with the AC off, since capacitors can hold charge. Only a technician should handle it.
Never open the outdoor unit, refill gas, bypass a sensor or jump the compressor. These are unsafe, can void the warranty and may destroy the compressor.
What a repair costs more for
A capacitor or fan repair is small. Replacing a compressor is the biggest single cost in an AC, and it rises with the size of the unit, the labour of evacuating and refilling, and whether the AC is out of warranty. On very old units the repair can approach the price of a new AC, so ask for the part named in writing before saying yes.
How to avoid compressor trouble
Clean the filters monthly, service the outdoor coil each year, avoid switching the AC on and off quickly, fit a suitable stabiliser, and keep the outdoor unit shaded and clear. If cooling has been weak for a while, read AC not working and call service before the compressor strains. Your fridge runs on a similar compressor, so fridge not working may also help.
Frequently asked questions
How do I know if my AC compressor is not working?
The air stays warm, the outdoor unit is silent or only hums, and there is no steady running sound. Only a technician can confirm it with a meter and gauges.
Why does my AC fan run when the compressor will not start?
Fans have their own circuits. The compressor may be waiting on a capacitor, cut out on overload, starved of voltage or worn out. A technician has to test it.
Why is my AC outdoor unit fan not working?
A failed capacitor, a worn motor, a jammed blade or a board fault. Do not open the unit; book service so the compressor does not overheat.
Can I fix a window AC compressor myself?
No. The compressor is in a sealed system with refrigerant and mains power. Only an authorised technician should check and repair it.
Is a clicking sound from the outdoor unit serious?
It can be. Hum and click repeating often points to a capacitor, a supply issue or a stuck compressor. Switch off and call a technician.