When ever I set the thermostat to heat or cool the transformer blows. I have installed a 2a fuse in line to protect the transformer after 2 cooked . I can switch on the fan and it works until I call for heating / cooling then everything quits. What would be the possible things to check?
Thanks for any help.

Do you have a heat pump or gas furnace? A 2 amp fuse may be a little low. Most systems will use a 3 or 5 amp for protection. If you have a heat pump you need to check the out side unit for low voltage shorts. (Pressure switches and defrost thermostat.)

Do you have a heat pump or gas furnace? A 2 amp fuse may be a little low. Most systems will use a 3 or 5 amp for protection. If you have a heat pump you need to check the out side unit for low voltage shorts. (Pressure switches and defrost thermostat.)

It is a heat pump with a gas furnace. I will get some heaver fuses and check for shorts outside. I will post the results.
Thanks