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GM AC blues

Anonymous on Thu August 28, 2003 12:54 AM User is offline

Year: 2001
Make: Chevy
Model: Silverado
Engine Size: 5.3

Okay here goes, if you are familiar with GM AC controls, when the

Blower is ON
The AC request light is ON
The Recirculation is ON
and you switch the AC light OFF, the compressor stays engaged.

But when you switch from Recirculation to OUTSIDE Air mode, and switch the AC request button ON and OFF the compressor engages and disengages like it should.

So the only problem is when the AC is in RECIRCULATION MODE the compressor does not disengage like it should when the AC BUTTON is turned off.

Is this problem in the HVAC CONTROL MODULE (the dash control unit) or in the PCM MODULE (which controls clutch engaging and disengaging).


Mitch on Thu August 28, 2003 8:03 AM User is offline

I believe that what you are seeing is normal. Certain GM cars and trucks will not allow recirc mode unless the AC is also on.

The recirc mode overrides the OFF switch and keeps the AC on. You have to go out of recirc before you can turn the AC off.

GM Tech on Thu August 28, 2003 8:37 AM User is offline

Many have noticed this- it is by design to function as you describe.......

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Thu August 28, 2003 9:00 AM User is offline

Wonder what the thinking is behind this? Or is there? Next thing they will do is automatically roll up all the windows when you put the car in gear. Dang doors lock now and in some Ford, the seat belt flies back to knock a cup of coffee out of your hand. That hurts. The main function of an anti-thief system is to keep the rightful owner from starting his vehicle. Any thief worth his salt will drive that vehicle away in seconds. The ones on crack use a brick or stick a gun in your face.

Recir doors use to recir, controlled by a cable, could be set for any degree of recirculation, then they slam full open or full shut, but now only recir about 70%. What is wrong with an AC switch? There are times when you need defrost, but don't need that cold blast of air that condenses moisture on the windshield so you can't see where in the hell you are going.

Today, you are strapped in a vehicle in a small uncomfortable seat with absolutely nothing to do except hope and pray that a warning lamp doesn't come on and have no control what your MVAC system decides to do. But the driving public is considered to be idiots, so we have even more idiots deciding which functions to control. And in many cars, you can't even drive them unless the AC system is working and if even that two buck blower motor goes, you are dead.

Mitch on Thu August 28, 2003 9:57 AM User is offline

I believe that the theory is that the only time you really need recirc air is when it is extra hot and the AC could not keep up with outside air. Some GM models switch to recirc without the driver's consent when AC high side gets too high.

Recirc in heat and defrost modes should never be necessary unless you live in Siberia and the temp is -92F. In the old days, even cars without AC had a recirc mode on the heater, but I can't remember ever needing it even at 0F ambients, though,I have never been to Siberia (I mean WI) in the winter.

The purpose is to reduce the possibility of Carbon Monoxide poisioning, but I guess it's OK to risk it to keep your cool.

What surprises me is that there is no consensus within GM concerning the best way to present all of the driver controls. For the last 5 years, I have rented dozens of GM cars and there is quite a bit of difference between the various lines on AC controls, cruise controls, window wiper controls, headlights, etc.

Edited: Thu August 28, 2003 at 10:06 AM by Mitch

MrBillPro on Thu August 28, 2003 10:01 AM User is offlineView users profile

On my 98 GMC if I turn off the a/c switch regardless of the position of the recirculation switch my compressor go's off. I have turned it off many times when I was about to get frostbite going down the road and it allows the freezing air to recirculate for a while and keeps it pretty comfortable for a while then when it continues to warm a little to were I am getting a little uncomfortable, I hit the switch again and here comes the ice cycles. This really is beneficial to me for two reasons I for one believe it or not do not like to be real cold "not to good for me in and out of 135 degree attics all day" just comfortable and in the early morning time after it removes the humidity and get nice and cool I can switch the a/c off for a while like maybe ten minutes or so and just let the air recirculate and it stays fairly comfortable I guess maybe because the cab is well insulated or maybe a better word tight don't know.

Don't take life seriously... Its not permanent.

NickD on Thu August 28, 2003 10:11 AM User is offline

There are times when having a full recir door is fine, farmers around here burn fields, getting stuck behind a smoke blowing truck or more in particular the city owned diesel powered school buses that stick their exhaust pipe in your fresh air intake much like a tanker aircraft wood, passing some of these paper or pulp mills, we hit a city in Canada mid central of Lake Superior, and God that place was bad, eyes started burning as did the lungs, was way out in the woods. If you have a baby in the vehicle and don't want to roll down a window, being able to slam that recir door shut when hitting such things like this is nice as it takes a while for that smoke to clear up.

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