I posted this a while and didn't get any responses so I'll give it a 2nd try.

1997 C1500 2WD 5.7L. The truck AC runs fine when truck is moving. After sitting (only on hot days) for 5-10mins it'll start blowing hot air. So in bumper to bumper traffic here in Texas at 100+ degrees, I'm screwed. Once traffic clears up I have to shut everything down and drive for about 5-10mins then turn it back on. At that point it'll start blowing cold.

I mentioned "only hot days" because at night, temps below 80 I can't let it sit idle and the cold air stays consistent.


Any ideas?

 

Most likely low coolant. Hook up some gauges and check it all out.

Also you might want to check the rest of your components. Could be a sign of something going out like the evaporator, condenser, etc.

 

YUP! Low on Refridgerant R134a? my truck does the same thing

 

Ok gang. I pulled out my guage and tested it. It wasn't low. In fact ot was about 85% and to be certain about coolant level, I added more without without hitting the red area.

I then ran the truck for a while mid day today, then let it sit in my driveway and started blowing warm air after about 15-20mins.


Any ideas?

 

With it setting in idle, blowing hot air, with a/c on, is the compressor clutch engaged? If not, and I suspect not, check for voltage at the clutch electrical connector, if you don't have 12 volts there, check for a low pressure cutoff switch issue. I don't think temp has anything to do with it.