I have an 94 f150 AT and am having ac/defrost problems. When I turn the dial to ac or defrost there is a horrible clunking noise and it causes the truck to stall out. Has anyone heard of this problem or know what is going on? Is it just a bad compressor? Any help would be appreciated.

 

It sounds like your compressor/clutch is bad. To isolate the clutch or electrical something, disconnect the plug on the compressor/clutch and turn on the switch. If it dies, it's another electrical problem; if not, bad clutch/compressor. There are shims (they looked like washers to me) in the clutch assembly; you might check to see if they are there or not.

I'm not an HVAC guy, just an experienced owner.

 

Thanks, that worked! I unplugged the electrical switch from the compressor and turned on the switch inside and had no problems. I know now that it is a bad compressor.