My central ac works for a 1 or 2 hours then fan on the exterior unit stops turning (motor still running) and shortly after hot air comes out of the vents. I will then shut it off, by turning off the thermostat for about 2 hours and it will work again for about 1 to 2 hours. Unfortunately for me, the technicians (from my Insurance Co) always show up during 1 to 2 hour when it is working? Hence, they give it a clean bill of healthHelp me please!