matth

2006 chevy 5.3 125k miles runs great until you turn on ac or defrost then the motor starts running horribly the check engine light flashes the wierdest exhaust smell pours out the pipe and eventually shuts off. its not every time I use the ac but atleast 80%.I know defrost causes the ac compressor become on but I can't find where the compressor is locked up. also I know the electric cooling fans come on with ac but sometimes the fans don't and when the truck messes up and shuts off the fans stay on until I turn the key forward to accy then they will cut off. something screw going on I'm beginning to think pcm. any ideas?

in2pro

Welcome to the forum
I'd check to make sure the battery is healthy as well as the charging system...
May also want to consider cleaning the throttle body, as well as checking the operation of the Idle Air Control valve IAC...

Those are the things I can think of that would affect idle when the AC is turned on and the engine is loaded...

matth

new battery alternator checked out good throttle body cleaned this weekend and I don't believe mine has the iac valve. just put it on the scanner and when I hit the ac button the cylinders start missfiring like crazy then cut the ac off they quit missfiring.

in2pro

As a check, you might try disconnecting the power connector to the AC clutch and then turn it on and see if you get the same or similar results... that should tell you if its the actual load of the AC or if its an electrical issue in the circuit...

matth

already tried that and pulling the belt off it is definitely only when the ac is fully hooked up and operating with a load on the engine. what are the chances the cheesy autozone alternator tester doesn't pull the right load the ac does and it looked good on their machine but fails on the truck? I can't figure this out I'm definitely thinking electrical though because every time it did it to me tonight which was every time i turned on the ac but every time the truck went downhill was 30 seconds to a minute after the ac compressor clutch was engaged and spinning cold air blowing then the electric cooling fans cut on and everything went to cap shuddering and missing like crazy.

in2pro

Hummmm...

What about with the clutch connected but the AC belt off ( no compressor physical load) but that should engage the clutch and circuits and make the fans come on... the fans are a pretty good electrical load....

matth

runs fine with belt off but power to the compressor and fans running

Chevrolet Customer Service

matth,

I am sorry you still can't pinpoint the concern. If you do choose to have your GM dealership look into this concern please let me know so we can assist.

Erica Tiffany
Chevrolet Customer Care

in2pro

Lets think about that...?

I can't see the compressor loading down the engine like that, you'd think the belt would slip break....
I'd duplicate that test with all possible scenarios, vent blower on too....
How could the load of the AC compressor stall the engine...