This isn't a problem running around town, but I just drove about a 3 hour trip over the weekend and the AC after about 1 1/2 hours got warm and stopped blowing hard...

Seems that it could be Freezing up, if you turn it off for about 15 minutes, it blows like it should again... Lots of water pouring out the bottom when you stop...

Any thoughts...??

Thanks...

Mine does exactly the same thing, interested in what you find out here.

Definately freezing up. Probably low on charge.

Definately freezing up. Probably low on charge.

Yep, been there done that! :eek: Higher Humidity, High fan speed, low coolant = freeze up. Have the system checked out, and lower the fan speed to about 3 or 4. :ro)

Mine was doing the same thing 2 years ago.

Stealer replaced a "thingy" and it's been fine since.

Can these systems be re-charged yourself or do you have to take it to the stealer? I have seen kits as a local auto parts shop that allow you to re-charge A/C systems.

I looked but couldn't find the post. There is actually a TSB out there about the AC not working properly when the temp outside is above 90 F , look around and you should find it. Hope this helps

I have the same problem..on long trips the a/c gets less cool....interested in what you find out..

Mine did the same thing. First they replaced the climate control head. It still did it so they replaced the low pressure switch and it has been fine since.

I dont know the TSB, but I know they have an oriface that they are opening up a little bit. I am having my Pump changed right now...It had significantly dropped my mileage and the clutch would spark when engaging...not good. Does anyone know if the A/C is covered under the 100k warranty? Sounds like its gonna cost $500 for the pump itself..
jason

[quote=MaxFarmer;640965]I dont know the TSB, but I know they have an oriface that they are opening up a little bit. I am having my Pump changed right now...It had significantly dropped my mileage and the clutch would spark when engaging...not good. Does anyone know if the A/C is covered under the 100k warranty? Sounds like its gonna cost $500 for the pump itself..
jason[/quote

Not listed in my owners maual under the 100k warranty.]

The compressor is not covered by the powertrain waranty.
Your problem definately is evaporator freeze up if poor cooling ALONG with poor airflow but is not caused by low charge. If it is low on charge the low side pressure will drop and the pressure cycling switch will disengage the compressor.The only way a low charge can ice an evaporator is if the low pressure cut off switch does not cycle out(usually about 30psi).Too high of fan speed is also incorrect.The higher the fan speed the LESS likely the evaporator will ice.The cause is running long distances with the ac on max air or recirculate. This causes the air from inside your vehicle to be recooled and is therfore much more efficient than outside air at 100+ degrees. Once the inside cab temp stabilizes and you are comfortable you may have to switch to outside air because the air in the truck is already cool and you're recooling it causing this ice up condition.The thermal load on the evaporator is less and the low side pressure drops to just above the cycling pressure and the evaporator starts icing. Once the air flow is restricted there is less flow to warm it up and it just compounds the problem till no air flow.You should allways use recirc for best performance but shut it off on long trips if the cab temp will maintain.
Moisture in your freon can cause a freeze up of the orfice tube and poor cooling but NOT poor airflow. Tim

Thanks Tim,
You seem very knowledgable on this subject! I know mine will absolutly freeze you out for about an hour or so, then it slowly warms up along with the airflow slowing down. I thought it may be freezing but wasn't sure, why i thought that was because of the 2 above issues along with an excessive amount of water draining when i stopped to fill up........i'm sure i'll catch h*ll for this....... with gas. LOL Tim. Yes, my name also.:cool:

Have you recently added a grill mod, lift kit, or another flow affecting change that would affect air across the condenser? Extra hi humidity lately?

Midwest pretty much nailed everything on this.

This isn't a problem running around town, but I just drove about a 3 hour trip over the weekend and the AC after about 1 1/2 hours got warm and stopped blowing hard...

Seems that it could be Freezing up, if you turn it off for about 15 minutes, it blows like it should again... Lots of water pouring out the bottom when you stop...

Any thoughts...??

Thanks...

There is an updated low pressure switch. Mine went out and the AC would blow warm intermittently. Basically, the system incorrectly senses low pressure for refrigerant and won't engage the compressor. Lurking here for the last couple of years, this looks like a common problem. I would look at this first, since it is a very cheap fix.

There is also a TSB to put in a larger accumulator to get better cooling capacity - but this is a different issue from the one above.

Another point is that I had manual controls on my '03 and always left it in recirculate mode. I notice that my new '05 (which has auto climate controls) is very smart about popping in and out of recirculate based on outside temps - it probably has no idea of humidity though. If I were in a really humid climate - I would probably have to pop it into recirculate mode manually in order to get the AC to cool the air rather than dehumidify the air (which takes alot of energy - water changing state).

- jeff

Check the cycle switch on the side of the accumulator for a brown rubber band... if it has one, replace the switch.

The cheapest way to figure out your problem is to get a pressure meter, available at any autoparts store for about $20. These hook up to the low pressure side. You can also fill if necessary with them. Low freon can cause freeze up. I had an Eagle Vision that this happened to all the time. Had a slow leak somewhere in the system. Usually, it will only freeze up during very high humidity conditions. The advice on recirc is also good advice.

As Midwest said; very high humidity and recirculate will do it. I stop every couple of hours on a long trip, turn the AC off for a few minutes and the engine heat will melt any icing really quick. Normal procedure in the hot humid south. Not just on GM, did it on my 2 prior Fords too. If you don't want to stop often just switching to normal AC (inside/outside air mix) will do it.

The difference in these complaints is the lack of air flow. It is not a pressure switch or grill insert that would cause lack of air flow out the ducts. Yes there is a pressure switch issue for no cooling but air flow will be normal and the compressor will not be engaged.If you restrict the air flow across the condensor the high and low side pressures will climb and evaporator temp will also climb, therfore warmer air but good airflow.
The trucks with no recirc button still cycle the recirc door. The AC processor monitors high side pressure and with a higher thermal load the high side line pressure will be higher and the command is recirculate. As the thermal load diminishes the high side pressure also drops and I believe somewhere under 340 psi (high side) the recirc door closes.The recirc door opens at 420 psi even if not comanded. Don't spend your money on the switch or accumulator they won't fix your issue. Tim

The AC on my '04 is for crap. Its been in the 90's for the last few weeks here in Maryland. I had my truck at the dealer a few weeks ago to have the AC looked at and the said it was a little low on freon and they changed the programming on the climate computer. Whatever they did to it did not make a diffrence. It goes back the the dealer tomorrow to have the AC looked at again. I bought a temp guage and its been blowing 75-80 deg. air when the outside temp is in the 90s. But when the outside air in the 80s with low humidity the AC temp is in the 50's.

My '03 works for crap also. At 95 degrees outside the thermometer stuck in the AC vent only goes down to 62. I'm definately NOT icing up with this one.

Getting close to warranty expiring. Better visit the dealer.

For those with less than desirable AC performance. Check to see if you have a Denso AC compressor (I think the other option is a Delphi). If you do have the denso compressor, then print out the following TSB and take it to your dealer (applies to 2002-2004 lly and lb7).

http://www.dieselplace.com/forum/showthread.php?t=12476

I thought my 2003 worked okay until I got my 2005 - man it cools it right down....

- jeff

Sorry midwest - I didn't read your whole reply before - you obviously know alot more about it than I do.

My logic behind using the recirculate mode is that by leaving it in this mode - you will dehumidify the air in the cab and after it is dehumidified there will be less condensation and less chance of freeze up. So, I was thinking that in a humid environment it would be better to leave it in recirculate mode with a lower fan speed (to avoid freeze up and get better efficiency). Anything wrong with my logic?

thanks,
jeff

I had the same problem with my 2003 Duramax air conditioning system. I mentionioned it to the dealer before I purchased the truck. They said they fixed it, but on the sixty mile trip back home the air was not working worth a damn. I had a previous problem on a Ford t-bird so I thought I'd check my Duramax for the same thing. I put a pressure meter on the low side valve and the needle instantly went 3/4's of the way into the red danger zone! PRESSURE TO HIGH! When this happens the air conditioning will act like it has no charge and will not cool. I have no idea why the high pressure sensor switch did not kick the system off! Here's what I did, I took an awl wrapped a rag around it to keep the mess down and my hand from freezing. I backed the pressure off and kept checking it with my gauge. When the gauge read normal I put the cap back on and took the truck for a drive. Now it freezes me out of the cab! Last week it was 106 degrees here in Grand Junction, CO. The highest temp ever in the history of the city.... it was still cold in the cab of my Duramax. Hope this helps.

I dont know the TSB, but I know they have an oriface that they are opening up a little bit. I am having my Pump changed right now...It had significantly dropped my mileage and the clutch would spark when engaging...not good. Does anyone know if the A/C is covered under the 100k warranty? Sounds like its gonna cost $500 for the pump itself..
jason

Opening that orfice will cause the cooling temp to be raised a little(less evaporation) . You should be able to get a compressor new/not rebuilt for $375 plus installation.Sparks in the clutch? fuse should have blown fast.I just replaced the compressor in my old truck( now owned by grandson) and in wifes RoadMaster. Got a special, two for $900 installed.Now the fan control head on the Roadmaster crapped out. Only got 47K on the RoadMaster so I have to keep it.

Max Payne, to change the cycle switch that you're talking about, do you have to have the r134 drained to switch the switches? I have one with a brown rubber band on it and even after my new compressor while driving the same I can actually hear/feel my interrior fan will slow down when the compressor kicks on and then when it kicks off my blower seems to speed up and the air warms up. Or its switching out of recirc. Its a clear difference though. And, I changed my cab filters less than a month ago. I though they might have been my problem at first, but I guess not.
Thanks again,
Jason

Dmaxlover, Max A/C is the proper operation in warm humid conditions for best performance but once cab temp is mantained it may not be necessary any more to maintain cab temp. Short trips and around town use max but long trips after awhile no recirculate.
Evaporator iceing is a result of the evaporator temperature not the mosture in the air.Once the cab temp drops and you mantain recirculation the thermal load on the evaporator drops,the low side pressure drops, and evaporator temp can actually drop under 29* and thats when the evap freezes.There will allways be some moisture in the air (unless we live in a vacuum) and then it freezes on the evaporator.Lower fan speed also amplifies icing.Remember it's Evap temp and less fan speed means less air flow through the evap to warm it up.
Others reading post, this is only about poor A/C performance after long trips.If you have poor cooling all the time proper diagnosis will need to be performed. Tim

Thanks - that makes perfect sense to me now and it is how my AC is operating when I put it in auto mode. (recirc and max until cab cools down, etc.)

- jeff

The a/c will ice up if the humidity is high and the temp is kept on max even when it is charged. I have several do this over the years. I found that when the humidity is high that the temp should the turn just a bit towards the warm side and it will still cool well and not ice up.

There is also a problem according to the dealer with the systems that have the dual temp control where one side is warmer than the other. I noticed it on mine when the weather was a little cooler and the ac was off the air from outside was warmer on the driver side than the passenger side. I talked to the dealer yesterday and he said they have been told by GM about the problem and they have had three in this week and mine goes in Monday. Mine is an 03 and thank God for the extended warranty.

Tom Cobb

So once the cab is cool, you turn Recirc off and leave the AC part on? I've been turing the AC off and leaving the Recirc on and it stays pretty cool. Is this wrong then?
Jason

Tom please reread the post again.The reason it freezes up is because your running max too long. Max air is just recirculation. The temp door is after the evaporator in the air flow and has no direct effect on evaporator temp just air mix between heater core and evap affecting air duct temp.The reason the temp adjustment helped is because once off of full cold it shuts off the recirculation mode.you can leave it on full cold if you manually shut off the recirclation/max button.Once again it's evap temp that causes icing not humidity.

Listen to Midwest!!!!!!! I took a trip from DFW to south central Oklahoma today for my fathers birthday, this trip takes about 2 1/2 hours. The temp was about 98 degrees and i was going to start out with the a/c in recirculation mode to get everything inside cooled off and then change it from recirculation to outside air intake. Well, talking to my Sweetie, and about half way into the trip, playing around with a white dodge for a few miles, i forgot all about it and it froze up. On the way back this evening, outside temp was about 95 degrees and i started out with the recirculation mode off, a/c on high, when it got to cold i turned the temp control from 66 to 76. It worked fine the entire trip, never froze up, no loss of airflow through vents. I think Midwest is the a/c man here. Thanks!:hail:

Contrary to what you say midwest I have never had a freeze up on the current or earlier trucks in max air (recir) mode, only in when outside air that is very humid is coming in. I have been driving GM trucks for 25 years and they all have done what I just stated. I do know what I am talking about.

Maybe that is not what happen to the others but that is what has alway happen with mine.

Tom Cobb

Tom reread your last post then. You stated yours only freezes in high humidity on recir.If in recirculation it is using inside (less humid) air not humid outside air. This cause less thermal load on the evap and after awhile the evap temp drops.There is a higher likelyhood of freeze up in higher humidity because there is more moisture in the air but it's not the moisture that's the problem.If you run NON recirc even in high humidity the evap temp can not cool to freezing temps because of excessive inlet air temps from fresh humid air comming in from the cowl area.All the humidity in the world won't freeze the evap untill the heat load disapates enough to drop evap temp. (It"s the evap temp not the humidity!!!)
When you move your temp knob off full cold it opens the fresh air door and that's why it no longer freezes up.Also too slow fan speed in high humidity causes freeze up.If it's too cold move temp up but maintain higher blower speed.I guess we'll agree to disagree.

I'm glad I'm not the only one with this problem. I've experineced this several times and every time it was while towing a travel trailer and the outside temps in the upper 90's. Each time it happend was after about a two hour haul. Had not happened last year and only once this year last week. I cut the air off for about 15 minutes and it worked fine the rest of the trip. Matter of fact on the return trip it did not happen but the temps were in the 80's. Dealer originally said it was a bad connector. Thanks for the tip on the recirculate mode.

my air did the same thing and the dealer changed the a/c cycling switch. all is cool now.):h switch # 9.172 i believe.

they replaced my acumulator thingy and it blows ice chunks now.

Your's was not the same if a pressure switch fixed it.A pressure switch would not affect the air flow volume out the ducts just the temp.Evaporator freeze up causes poor air flow.The switch problem causes the compressor to not engauge causing warm air but plenty of flow.It is remotely possible if the switch didn't cycle out the compressor under 30psi AND it was low on charge it could freeze up but it too would have poor air flow.2 problems not very likely. The switch has been an issue though just not this problem. Tim

Does the R134 need to be drained to change the pressure switch on the accum?
Jason

No, it will just make a quick pop/hiss as you unscrew past the "o"ring. There is a schrader valve in the fitting.

Any Body Change The Cabin Air Filter? Did It Solve The Problem? Or Did The System Need To Be Recharged?

I have to change my cabin filter AT LEAST once a year. Granted, Im in some pretty dirt conditions. It does make a difference on how fast your blower blows....I'd bet it could help freezing up to an extent. BUT, if I remember right, only the '01's have the cab filter?

Thanks midwest. I think I'm going to look in to changing that sensor to see if I get back to what I remember my AC to be.
Jason

Guys I need some serious help with my '03 dmax. My A/C will work properly and then intermittently the driver side will just all of a sudden start blowing extremely hot air. The passenger side will continue blowing cold air. In this Texas heat, this is really starting to get frustrating. Does anybody have any idea on what this could be? I went to the dealer and they thought it was the accumulator switch thing, so I replaced that and about a day later it started doing the same crap. Any help or advice will be greatly appreciated. Thanks!!!

Do you have auto or manual contol haed. Either way it sound like the temp actuator on the drives side may have an intermittant feedback position problem.A competent tech should be able to diagnos. Tim

I have a LT which has the dual climate control. Please anybody??? Thanks!!

bumpety bump.........anybody??? It's gettin' freakin' hot in this Texas weather!!

Guys I need some serious help with my '03 dmax. My A/C will work properly and then intermittently the driver side will just all of a sudden start blowing extremely hot air. The passenger side will continue blowing cold air. In this Texas heat, this is really starting to get frustrating. Does anybody have any idea on what this could be? I went to the dealer and they thought it was the accumulator switch thing, so I replaced that and about a day later it started doing the same crap. Any help or advice will be greatly appreciated. Thanks!!!

The climate control computer need to be re-flashed. This happend to my 04 a couple weeks ago. Freaked me out when it happened.

I think the latest TSB is 02-01-38-007C I had it done last fall. It seamed to work OK until we took a trip to Las Vegas in July. It would keep it kind of cool at highway speeds, but driving around it would blow warm air. When I got home I took it back to dealer. They replaced the low pressure switch of the 4th time and lowered the charge a little. Since then I have driven in town and on highway at around 100 degrees and it cooled OK. Not as good as my wifes 03 Tahoe but acceptable.
:grd:

Tsb 02-01-38-007c Accumulator

My dealer changed my accumulator under the TSB over a year ago. It's been like a different A/C system ever since. It'll freeze me out now. Plus when it's over 90 degree's, I run my auto climate control in manual and set the temp. down to 60 degree's running the fan on manual also.

I don't think the '03's and up have cabin filters though.

I don't think the '03's and up have cabin filters though.
I have noticed one of the vender's here is selling a after market cab filter.
Cabin Air Filter Retrofit Kits now Available (http://dieselplace.com/forum/showthread.php?t=48973)
Might be worth looking into.