Sam J - arrived to new customers home to work on heat pump package unit. Customer explained that no matter what the unit wouldn’t respond. Began inspecting unit for obvious issues and determined I had no supply voltage inside unit. Breaker panel nearby had a tripped breaker responsible for the entire package unit system including heat strips and AC. Reset breaker then cycled system on and checked operation. Heat strips were pulling 40A and compressor was pulling 7.5A, both well within range. Allowed system to,run for several minutes while explaining the situation to customer and his son. Suspect the main breaker inside panel may be getting weak and tripping after long run periods. If problem continues the breaker needs to be replaced. System operating properly at this time.