84 Trans Am. I was driving down the road with the heater on and the blow motor stopped working. The blow motor works under all the air conditioning settings, but when I move it over to the economy (vent, heater, defrost) settings, I only hear a click and the fan stops working. I put a test light on it, under the ac settings with the fan working the test light comes on, but it is a very dull light. When I move it over to economy the test light is very bright, but the fan stops moving. Any ideas what is causing this problem?

 

Someone else will come along with a better answer but it sounds to me like the HVAC controls have just gone bad.
Good luck
Alex

 

Turns out just a bad ground wire. I took off the black ground wire at the back of the blow motor. Then I hooked up a wire to the back of the blow motor and grounded it straight to the chassis and the fan started moving.

The strange part is that my fan has 4 speeds (Lo-Med-MedHi-Hi). On the AC side all 4 speeds work. On the Economy side, I'm only getting 3 speeds (Lo-Med-MedHi) to work no Hi speed. I swapped out the fan switch and the relay under the hood, but no luck.

It would seem strange to have it only work 3 speeds from the factory. Does everyone's heater (Economy side) work on all 4 speeds?