: Strange observation on GM's AC system...



taken
06-24-13, 12:47 PM
So, I've owned a 2006 Chevy Express van, 2011 Chevy Express van, 2010 V and 2013 V. All have the identical quirk in the AC. It runs ice cold for 2-3 minutes and then has 10-15 seconds of warm. Then it's back to a few minutes of cold. All 4 vehicles did it the exact same way. Theories? No other brand of vehicle I own or have owned does this.

cruiser68
06-24-13, 01:25 PM
My V does not exhibit that symptom. If I get on it however, it does shut off the compressor until you get off it.

taken
06-24-13, 01:31 PM
Strange. I thought it was a GM thing as the Express cargo van and the V are pretty much polar oposites and both did/do it the exact same way. 4 vehicles all the same. Could it be a huge coincidence? Mine has nothing to do with RPM. Does it no matter what. Cruising along a back road at 50 and low RPM still does it...

MASCAD
06-24-13, 02:53 PM
Curious as to what part of the country you're in. Just tried my '11 CTS-V and it doesn't seem to act the way yours does (86 and humid) Does it do this when you first start the car, drive for a while etc. and does it ever not do it?

Trapspeed
06-24-13, 03:34 PM
Are you using the Auto setting? If so, that will do it every time unless you bottom it out or go all the way hot.

cruiser68
06-24-13, 04:11 PM
Are you using the Auto setting? If so, that will do it every time unless you bottom it out or go all the way hot.

Good point. I use auto and I can definitely tell when it gets gets cooled down as the vents do go from cold to "not as cold" but I wouldn't say warm.

RGaret
06-24-13, 04:21 PM
Good point. I use auto and I can definitely tell when it gets gets cooled down as the vents do go from cold to "not as cold" but I wouldn't say warm.

Mine does the same thing. I leave it on auto all the time. Not every 4 minutes but it does blow warm for a few seconds every now and then.

taken
06-24-13, 05:44 PM
Yep, on auto. However, my van's didn't have auto climate control and did the same. Your right, it's not really warm, just "not so cold" for a few seconds as mentioned above. I'm sure it's normal, just not sure why it cycles. Have Ford and Dodge vehicles, both with auto climate control, that never have this fluctuation.

Jinx
06-25-13, 02:38 AM
Maybe this is how they keep mold from growing.

MASCAD
06-25-13, 07:53 AM
Yep, on auto. However, my van's didn't have auto climate control and did the same. Your right, it's not really warm, just "not so cold" for a few seconds as mentioned above. I'm sure it's normal, just not sure why it cycles. Have Ford and Dodge vehicles, both with auto climate control, that never have this fluctuation.

Could this be caused by cycling of the compressor to prevent icing of the evaporator coil.? As the system senses that ice is forming it may be cycling the compressor off for a short while which lets the ice melt and would cause the air to be not so cold. After the ice is melted the compressor kicks back in and the air becomes colder again. Ambient conditions especially humidty would be a factor on how frequently this occurs.

taken
06-25-13, 07:55 AM
That makes a lot of sense. Could be... Wonder why GM has it and no one else does?

MASCAD
06-25-13, 08:15 AM
That makes a lot of sense. Could be... Wonder why GM has it and no one else does?

Not sure why you don't notice this on other vehicles. Ive seen this icing happen on marine A/C units under certain conditions so I'm thinking it must happen to every system if the conditions are right. After all, the air going thru the A/C unit is the same regardless of the make of the vehicle!

thebigjimsho
06-25-13, 11:24 AM
Once in a while the A/C cycles off for a few seconds in my Town Car...

mr weather
06-25-13, 11:45 AM
My wife's 08 Grand Caravan doesn't cycle and depending on ambient conditions (usually moderate temps but high humidity) the evaporator freezes up and I have manually "de-ice" it by turning the a/c off. What a stupidly designed system.

montgb
06-25-13, 11:12 PM
I noticed this behavior on my V today.

StoneCrab
06-25-13, 11:29 PM
All* properly running A/C systems will cycle the compressor on/off while running. This is done to prevent icing on the evaporator while still providing cold air. Low refrigerant levels or blockage of airflow across the evap or condensor (clogged filters, for example) can cause the system to not cycle and also not cool properly. I bet what you sense is the off cycle when the humidity/temp returns to the air temporarily.

*Some of the latest ultra high efficiency compressors do not cycle. They have variable displacement to adjust their cooling capacity based on demand. The Chevy Cruze ECO and some others do this instead of cycling on and off. Some of them are not clutched and always run, even when the A/C is 'off'.