Have you heard any abnormal noises or vibrations?

Have any error codes flashed during operation?

If you have a Multi zone system, did you ensure each indoor unit is working correctly?

Did you check the breaker size and wire gauge?

Did you check the voltage to verify it was within the correct limit?

Did you pressure test the system?

Did you check and verify the condensate drain line for leaks?

Did you check to make sure the system cycles in both Heat and Cool modes?

Were there any noises or vibrations when the system was running?

Did any error codes flash during the startup or operation?

If you installed a Multi zone system

did you test each indoor unit operation?