Outdoor unit won't come on, Outdoor unit not running: This is a very common problem, whether it's an air conditioner or a heat pump. And there are many things that can prevent the outdoor unit from starting, some of which can be quite serious. Unfortunately, many times a service technician is dispatched only to find a simple problem that could have been addressed, even fixed by the homeowner. Faulty contactor or capacitor Faulty thermostat cable or burnt wires Unit off due to an open safety device (low pressure, low temp, high pressure, high temp...) Thermostat not set properly Emergency or shut-off switch turned off Blown fuse in panel box Circuit breaker tripped or off Condensate pump unplugged and/or safety switch open Outdoor reset button tripped And before you place a Service Call...Learning Center » A/C & Heating » What To Do When Your HVAC Compressor Won’t Turn OnWhat To Do When Your HVAC Compressor Won’t Turn On