Hello,
I have a 20 year old electric furnace, both the outside and inside unit are called a comfort maker,and are made by a company called Inter city products.
The air conditioner works perfect, both inside and outside units. As soon as the thermostat is turned to heat, it blows the 3 amp fuse,both units do not function. I did replace the thermostat to see if that would help, the problem is still there?

Andy

Can be the control wire for heat shoted(white, most I see), or Maybe more likely, the Heaters Relay or Contactors Coil is shorted. Disconnect at the Heat contactor's coil, insulate, and if it doesn't trip, That Contactor/Relay appears bad.
A meter can help a lot, can be done without.
It will cost you fises?

Hello Stratmando,
Thank you so much for the reply! I switched the white (AUX) for a spare brown thermostat wire, at the thermostat, in the attic, and the outside unit.
I did replace the contactor, and the problem is still the exists. Sorry for the delayed response I had to wait for the part to arrive.

Thanks Andy