I have a 1981 Ford F-150 and the climate control system is giving me quite a headache.

The temperature slider is on cold and will not slide all the way over to the hot side. Stops about halfway with a lot of resistance.

The mode slider does not affect operation -- system insists on spitting out cool air from the defrost. I can have it set to "off" and the fan switch still acts normally, blowing air out the defrost no matter what the position.

I've been told to check for vacuum lines that are disconnected -- should I yank the control unit out and make sure the sliders are attached to their cables/or whatever?

Very difficult problem -- it was 95 degrees today and I'm very keen to fix this.

Any help?

Thanks,
Andrew