1996 f150 a/c auto, 351, 4x4. Ok now for the question, I replaced the originalam/fm cassette radio and replaced with new Alpine with all fittings from Crutchfeild. After installing new NO heat, the fan works fine, the controller moves the baffle under the dash, the selector works fine. Flushed the heater core with hot water for 30 minutes, replaced orginal thermostat also. had the heater core cover off and i was warm after driving 2-3 miles. The radiator is full as is the over flow tank. So now what? Its a little cold in there as the heat used to work and it was -7 last night.

 

Does it work if you use only floor heat? The 94 F150 I owned did something similar. When it was very cold and I used the defrost the heat quit working. I bought the truck a few months earlier and someone had bridged the switch on the AC can to keep the compressor from cycling and telling that it was low on freon. I am not saying that is what is going on with yours, but given the low temps it might be worth considering the possibility that the AC coil is freezing over. That is what happened to mine. If you have not already, you may want to recheck your flow through your heater coil.

 

If it only started since you installed the radio, you probably accidently knocked off or cracked one of the vacuum accuator lines. There is also a mix panel (hot cold switch activates) that limits air travel through the heater core box that is activated by a cable. It could have come off the controls or the panel control arm.

Sounds like you get to stand on your head for a while to see what happened.

 

Didnt see any vaccum lines with either control panel off. The cable/cables opperate a door to the left of the heater core, door is approximately 1-1 1/2" across, it does move, 2 cables go to the top of this from the temp controller, where the cables attach to this gate is red. Ill probably take the cover back off and really look had to see if something is blocking the entire flow from the front of the core. Any other IDEAS GUYS? Its cold here, good thing ive ggot my supercrew to stay warm in, but It is more like a family vehichle and the 96 is one of 2 farm vehichles, and neither heats very well now.