Hi, all. I'm new and I tried to do a search, but the search field won't let you search for ac, AC, or A/C, so I thought I'd go ahead and ask...

I have a 2002 Express 3500 with 350 and the A/C does these things:
It will work great and blow cold when I first start up IF i haven't run the vehicle for at least 3 hours or overnight. It will blow cold for sometimes 5 minutes, sometimes 10, 30, or more, but eventually it will quit blowing cold and go totally hot. If I leave the A/C off and try to "save" it, while I run the vehicle after it has sat for the 3 hour or overnight period, then turn on the A/C later, it won't blow cold at all.
Also, if at any time that the A/C is blowing cold I turn off the engine, it usually will blow hot immediately.

There's pressure in the system and when it works, it works great. I'm hoping there's a pressure sensing switch or something that needs replacing.
Any help is greatly appreciated.

 

Sounds like a problem with the blend door actuator or the control for it.

 

A/C systems are basically the same, being in a van or whatever. You should with it running, and a/c on see if the compressor clutch is engaged. If not or intermittent have the freon checked. With an 05 I'd not think unless you've had an adnormal issue a freon leak. Have it checked, if it is low, have it serviced with leak detec freon.
I have a 12 year old suburban that air works great, and have never had to have it serviced.

 

I agree, check the compressor clutch for engaging while the AC is on and the problem is present...
here is some good reading on the subject...
http://www.aa1car.com/library/ac98.htm