I have a 93 Chevy S10 extended cab pickup with the 2.8L V6. Does anyone know why my ac switches from the dash vents to the defroster vents when I am going 65 and when I let off the gas it switches back to the dash vents? Any suggestions?

 

if the system is vacuum operated....and you have a vacuum leak; the door will change position at that time as engine vac is low at high throttle opening and vac is high at closed throttle. d o you hear an air hiss at closed throttle? most of these vehicles have a vacuum reservoir for wot conditions....is your missing or leaking?

 

Haven't heard any hissing. I don't know if it is missing or leaking but thank you I will check that out.

 

It has the vacuum reservoir and all the vacuum lines look good. I don't hear any hissing noise in the engine compartment but I do hear a hissing sound in the dash when I turn off the ac. Also with the ac on it will idle high for a few seconds and then idle down when I stop at a stop sign.

 

hissing from ac shut down is the high side pressure equalizing as it passes thru the orifice tube.
find the hvac box vacuum actuators and make sure they have vac with the engine idling.