My old system, it died and was replace last year, had a 5amp blade fuse ( basic car type fuse) located on the air handler in my house that when it blew prevented the heat pump from turning on.
Might be worth looking for if you can access the air handler.
I found a capacitor in a local supply shop for HVAC and plumbing when my system died. Replaced it and it didn't bring it back.
