Common HVAC Problem
Outside AC Unit Not Running?
Your indoor fan is blowing, but the outdoor condenser is completely silent. This is one of the most searched HVAC problems — and it usually comes down to one of four causes.
Common Causes
Why your outside unit isn't running
A silent outdoor unit doesn't always mean a major repair. Here are the most likely culprits, from most common to least.
Capacitor Failure
The run capacitor provides the electrical boost your compressor and fan motor need to start. When it fails, the outdoor unit may hum or click but won't actually spin up. This is the single most common reason an outside unit stops running.
Tripped Breaker
Your outdoor unit has its own dedicated breaker. A power surge, short circuit, or overloaded system can trip it. Check your electrical panel — if the breaker for the AC is flipped, reset it once. If it trips again, there's a deeper issue.
Contactor Failure
The contactor is an electrical relay that turns the outdoor unit on and off based on the thermostat signal. Over time, the contacts can burn or pit, preventing the circuit from closing. The unit simply won't receive power.
Thermostat Wiring Issue
If the signal wire between your thermostat and outdoor unit is damaged, disconnected, or shorted, the condenser never gets the command to turn on. Everything inside may seem fine, but the outside unit stays silent.
Run the AirWise diagnostic to identify the issue.
60 seconds. Clear answers. Cost estimates. Optional contractor match.
Full diagnostic report for $19.99. Free health score available.