88/94 hvac question

[Murd450]

I have a 94 with ecc . Yesterday I noticed sitting I a parking lot waiting for my wife , my max ac would turn off and back on by it self every 10 min or so . Why did it do that ? It has never done that going down the road .

 

[4thesporty]

Timely question! I just noticed mine doing this over the last week.

Usually when I start the truck and turn on the AC I leave it off MAX till it cools down a bit. Sometimes it will automatically turn on MAX, or REC for a few moments, then turn it back off. I thought my ACC unit is starting to go or something.

 

[Murd450]

Mine didn't work at all till Sunday . And you being in dfw know it sucks here when the a/c don't work . I found all the blend door motors unplugged . I plugged them in and now it works . But seems to change all on its own every so often .

 

[4thesporty]

I've noticed mine usually does it after my truck has sat out all day at work in the parking lot; REC will come on shortly after I turn on the A/C and then turn off maybe 30 seconds later. If I later want to turn it on, it works as normal. IDK.

 

[great white]

"max A/C" actually is just recirc.

It keeps recycling cool cabin air to make it colder rather than drawing in ambient.

There's diminishing returns there though as it will eventually fog your windshield (from you breath being recycled). that's why it disables recirc if you're on defrost.

To the best of my knowledge, the GMT 400 AC system is a "dumb" system. meaning: you set it and it drives to that setting regardless of temperatures as it has no idea what the temps are anyways.

If it's going on and off recirc uncommanded, you probably have a repair bill in your future. Possibly the head unit as that's where the control is. Not much in there either.

Or, just run it an chalk the behavior up to another one of those "old truck" idiosyncrasies.....

 

[4thesporty]

Yup, and worst case scenario is I need to replace the unit. They're a dime a dozen in the yards.

 

[1997chevydriver]

"max A/C" actually is just recirc.

It keeps recycling cool cabin air to make it colder rather than drawing in ambient.

There's diminishing returns there though as it will eventually fog your windshield (from you breath being recycled). that's why it disables recirc if you're on defrost.

To the best of my knowledge, the GMT 400 AC system is a "dumb" system. meaning: you set it and it drives to that setting regardless of temperatures as it has no idea what the temps are anyways.

If it's going on and off recirc uncommanded, you probably have a repair bill in your future. Possibly the head unit as that's where the control is. Not much in there either.

Or, just run it an chalk the behavior up to another one of those "old truck" idiosyncrasies.....

The ones in my 94 and my old 92 went to max or recirc by themselves and shut off by themselves. Im pretty sure its normal

 

[4thesporty]

Well, I doubt that it's normal, probably more like a normal failure

Like great white stated, this is a "dumb" system; there is no automatic control of the climate control.

 

[1997chevydriver]

Well, I doubt that it's normal, probably more like a normal failure

Like great white stated, this is a "dumb" system; there is no automatic control of the climate control.

Nope. It's normal

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[great white]

Nope. It's normal

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Well there ya go. That funky control head in the 88-94 dash must have a thermistor in it.

Mine never did it but i guess it never had to.

Proof that I don't know everything.......