This is not an unusual problem whether it is an air conditioner or heat pump. Unfortunately, many times the service technician finds a simple solution that the homeowner could have easily corrected and saved both the cost of a service call plus the inconvenience. can be addressed or fixed by the homeowner. usually require a service call. Emergency switch or shut-off  switch turned off Outdoor disconnect turned off Off on outdoor reset button Unit locked out (reset by turning off then turning back on) Here is a checklist to go through before making a service call: Make sure the thermostat is calling for heating/cooling Make sure no Emergency switches are turned off Make sure circuit breakers for both indoor and outdoor units are in the on position (reset for certainty) Make sure the outdoor disconnect is on Off, on safety device (low pressure, high pressure, low temp, high temp.) Hope this has been of some assistance, however they are just rough guidelines and not all possible conditions are covered.