I have a heat pump systems a LuxAire made by York it is ony 4 year old the model number is: F2FP048H06G

I have isolate all t/stat wire in and tested for possible grownding with negative result. I did rung the A/H fan on on and works find but when I set the unit for cooling or heating it blows the fuse.What oder test I can do? To make sure that the control board is good and to find the problem?

Thanks Harry Ruiz

If you have done all the low voltage wires and they were disconnected when you tested them I would jumper or twist together just the two heating wires and see what happens. This way you will know if the thermostat is causing the problem.

If that test is negative I would start looking for a low voltage component that is defective in the system.

Also check the wiring going from the inside unit to the heat pump especially if you have a dog or other animals. Sometimes they will chew through the outside signal wires for the system and cause a short.