sorry if this is in the wrong place i have a 98 blazer 4.3 liter v6 took my son to school today we were early so sat in the truck in the parking lot with the heat on truck shut off every time i tried to start it, it stayed on for like 2 seconds an shut off again turned the **** to off on the heat then the truck started, also ac doesn't work just blows air not cold not worried about the air i think i need a new compressor just wondering if the problem is related to the ac compressor or if something else going on any help would be appreciated. thank you

 

Let me get this straight: drove the Blazer to son's school and everything was fine but then parked with engine running, switched on the heat which caused the engine to shut off?

Or is it that the heat was off, engine off...and then turned heat on and then started engine which would only run for like 2 seconds. Only after turning the heat to off did the engine run normally?

Sounds like a large vacuum leak in the HVAC control. Suggest checking the vacuum lines under the hood.