My trane heat pump will turn on (the outside part ) then turn off after 5 seconds. It never cools the house. I had an hvac guy come out and he said the freon is full and that he could see no loose connections on the unit. He recommended I change out the new digital thermostat I had installed in the fall for one that is specifically for my unit. Before I did that I disconnected the thermostat and jumpered the 4 wires together that make it run all the time. When I did that the unit does the same thing.this eliminates the thermostat as the problem right? It just turns on for 5 seconds and then turns off. By the way when the weather outside is cooler it usually works fine. It will actually get too cold in the house but by mid day on a hot day it stops working . Where should I start to look for the problem?