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OldWrench · 08-23-2014, 01:25 PM

We have a 2008 Thor Four Winds on a 2007 chevy 3500 express chassis.
We recently took a long trip in some mountain conditions.
I noticed that the AC quit blowing cold air as we climbed very long hills that worked the Chevy hard.
I wonder if there is a check valve somewhere that is letting the vacuum leak out of a controller and the AC quits? I had this experience on a Volvo car before that when you pushed for more power the vents would shift from the top vents to the floor vents. I do not detect a change like that in the Chevy, the air just gets warm.
Also, the engine temperature climbs on a long hill, but it never seemed to loose any coolant.
I appreciate your thoughts on this minor problem.
Thanks

jamesrxx951 · 08-23-2014, 01:31 PM

Some clarification may be needed. It is a common practice when the engine coolant reaches a certain level the PCM will command the A/C compressor off to allow more cool air into the radiator. Since the condenser is before the radiator and the condenser expels heat, turning it off will allow a cooler air charge to the radiator allowing more engine cooling. Under certain throttle angles usually around wide open throttle the PCM will also command the compressor off. It may be due to protecting the compressor from high RPMs or even allowing more engine power to be transmitted to the drivetrain.

If you loose airflow out of the vents it may be a vacuum issue. I don't know how GM controls their blend doors but some early Ford vehicles used vacuum to control the blend doors. On long hills or in the case of slight vacuum leaks the vacuum is bled off and the air flow is diverted to the defrost vents.

OldWrench · 08-23-2014, 01:37 PM

Thanks for your response. My question remains whether this is normal for my chassis, or do I have a problem. Is there a system on the 3500 to turn off the compressor?

DonDee · 08-23-2014, 02:38 PM

My Astro did that. Vacuum leaks repaired and all was well.

ronjhall · 08-23-2014, 03:07 PM

Pulled the following information from my GM service manual for the 2007 Express Van.

Once engaged, the compressor clutch will be disengaged for the following conditions:

• Throttle position is 100 percent

• The A/C compressor cycling switch pressure is less than 124 kPa (18 psi) or more than 338 kPa (49 psi)

• The A/C high pressure cutout switch is more than 2896 kPa (420 psi)

• Engine coolant temperature (ECT) is more than 123°C (253°F)

• Engine speed is more than 5000 RPM

• Transmission shift

• PCM detects excessive torque load

• PCM detects insufficient idle quality

• PCM detects a hard launch condition

OldWrench · 08-23-2014, 04:44 PM

Thank You,
I recognize a couple of the variables you list as possibly the answer.
1)The transmission would down shift or I would manually downshift to control the hill climb.
2) It is possible and likely the PCM detected excessive torque load. The engine worked hard to climb the mountains. And I must admit I have more respect for GM after this trip.
A) It might be the coolant temp rising. I did see a climb on the temperature gauge but think normal is 220 and I saw 240 while climbing. It is very possible 253 was hit for short moments. It did not loose any coolant.
B) I never or seldom ever full throttle anything. 50 years ago is a different and another story. Being an old wrench I am careful to let the drivetrain live.
C) engine rpm. I do not have a tachometer. Even unable to hear as I am, that sounds like an annoying high RPM. But, perhaps it was happening and I got used to it. We have few gear selections. Drive and 3rd. I climbed many hills in 3rd to stop it from choosing 2nd.

ronjhall · 08-24-2014, 02:44 AM

I would try slowing down a little and use second gear when climbing steep grades. Try to keep temperatures as low as possible. For better gauge info, consider a Scangauge II.

OldWrench · 08-24-2014, 05:43 PM

thanks. I will check out the scangauge

sknight · 08-24-2014, 05:57 PM

It's normal. Under certain high load conditions the ECM disengages the A/C compressor to lighten the load on the engine. It actually happens a lot more than you know but it takes a few moments for it to be noticeable inside.

OldWrench · 09-02-2014, 05:16 PM

We were heading home yesterday on a 4 lane and I was just being lazy. I drove 60 or less. On the hills I could feel the air warm up coming out of the vents. I did not push the rig. We were heavy with a heavy tow.
I am not going to worry about it.
I am going to buy the scanteck recommended in a post. I might not enjoy setting it up, but I look forward to some of the readouts.
Thanks all for your help.
Pat
Old Wrench

toyzforme · 09-10-2014, 01:06 PM

Pat
I have the same issue on my 2013 chevy express 4500. I was told by the dealer it does this to offer more power to the coach. I find it kind of irritating especially down here in the south. I might try and find a way to disable it some day. For now I wouldn't worry too much about it.

Mich F · 09-10-2014, 01:46 PM

Quote:

Originally Posted by OldWrench

We were heading home yesterday on a 4 lane and I was just being lazy. I drove 60 or less. On the hills I could feel the air warm up coming out of the vents. I did not push the rig. We were heavy with a heavy tow.
I am not going to worry about it.
I am going to buy the scanteck recommended in a post. I might not enjoy setting it up, but I look forward to some of the readouts.
Thanks all for your help.
Pat
Old Wrench

Have you tried running the generator for house air, and turning off the dash air ?

toyzforme · 09-17-2014, 07:53 AM

I would think running the house air off the generator would use more gas than if you were using the air from the engine. Not to mention down here in the south there is a lot of heat that comes through the windshield so I don't see how this would be better. I could be wrong though.

Mich F · 09-17-2014, 08:36 AM

Quote:

Originally Posted by toyzforme

I would think running the house air off the generator would use more gas than if you were using the air from the engine. Not to mention down here in the south there is a lot of heat that comes through the windshield so I don't see how this would be better. I could be wrong though.

It's up for debate if running the generator for roof air uses more gas than running the dash air. I believe most generators use around .7 gal per hour. I believe it's more economical to use the generator, although that's not my main reason for running the generator and roof air. Living in south Florida I almost always use the roof air for cooling. I suggested he turn of the dash air because the engine's A/C compressor can make quite a difference in engine performance.