Compressor won't start

The compressor hums, trips, or does nothing when energised.

Refrigeration

high

Diagnosed here

Outdoor Unit Will Not Start
Troubleshooting
A structured electrical walk through when the condensing unit stays silent on a call for cooling.

Possible cause

Contactor
Component
The low voltage controlled switch that connects line voltage to the outdoor unit.
Run Capacitor
Component
What a run capacitor actually does for a motor, and how to tell when it has failed.
Start Capacitor and Hard Start Kit
Component
What a start capacitor does during the first moments of a motor start, and when a hard start kit is appropriate.

Affected equipment

Hermetic Compressor
Component
The pump at the heart of the refrigeration circuit, common types, and how to evaluate one before condemning it.

Local Code Notice

HVAC installation, venting, combustion air, ventilation air, gas piping, clearances, termination locations, electrical requirements, permits, and equipment requirements vary by jurisdiction and equipment. Always verify the applicable local codes, adopted code edition, regulations, permits, and manufacturer installation instructions before installation or service.