97 Sport.. cold in park, hot when I drive.

[syn-]

Ok, so I start the truck and turn my knobs to max a/c and 3 or 4 on the fan speed knob, as well as the cycling from the compressor about 3 seconds apart are the rpm drops (guessing on and off). if I sit parked my truck will keep me nice and cool. But if I put it in drive and begin to drive with the a/c on I get maybe a few feet? and then I hear a slight thud (roughly from where the glove box is located) and instant heat comes from the vents. I want to add I did just replace the HVAC controls.

 

[aldive]

What are the system pressures?

 

[syn-]

not sure, I don't have mani fold gauges, only a cheapo I got at auto zone.

 

[aldive]

You need to know the pressures to properly diagnose the problem(s).

Good luck ....

 

[wyochimneysweep]

its the blend door in the dash shutting is the should you hear. maybe a vaccum check vavle is bad and when you start driving engine vaccum lowers and the blend door shuts. thats my guess. i dont know it the blend door is electirc or vaccum

 

[TheJackal]

AFAIK all 2nd Gens have electric blend doors. The recirculate/outside air door is vacuum controlled, but you'd still feel cold air.

It's possible you might need to add refrigerant, but, as said before, it's a guess unless we know your system pressure. You can get a set of manifold gauges at just about any auto parts store.

 

[wyochimneysweep]

but most of the time i see problems it when idleing and works fine while driving. i think its another problem but that guess till you get gauge readings