AC (outdoor) not starting?

A failed outdoor control PCB cannot receive start commands or drive compressor and fan relays, preventing any operation.

Likely causes · most likely first

Control Board

Moderate DIY Part: $100–$280
Hermetic Compressor

Call a Pro Part: $250–$600

A seized or electrically shorted compressor will trip protection devices immediately, preventing the outdoor unit from starting.
Four-Way Valve

Call a Pro Part: $60–$180

A coil failure on the four-way valve solenoid triggers a fault code on some models, locking out the startup sequence.
Service Valves

Easy DIY Part: $15–$50

Closed service valves cause high-pressure lockout faults that prevent the compressor from starting.

See the faulty part in 3D.

Tap a highlighted part to see exactly why it fails, how to verify it's the problem, and how to replace it.