The other day I opened mine when I parked to keep it cooler. On the way home I couldn't figure out where the 100deg air was coming from with the A/C on full blast. Tried all the knobs, put them in every position - still hot air. What the heck? Stuck heater valve ? Failing new compressor? Couldn't figure it out.

Doh!

'69 1/2T stepside, Sea Foam Green, 250 L6 w/ 3 on the tree, not an option on it, in the family since new.