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Ok i have an 04 CCSB LB7 4x4 gmc duramax. 2 weeks ago the air start blowing warm. I took it to my local shop and the mechanic replaced the low pressure switch, charged me $37. yesterday I get in it and the passenger side is blowing ice cold and the drivers side is blowing very hot. Any help would be appreciated. thanks,
 

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Most likely its a servo motor that controls the vent door. Slim chance that you could take it to the dealership and have the ac reflashed, somtimes the computer needs to be "rebooted" according to what my service guy says. But more than likely its the motor. And be prepared if the dealership does it, its high. If you do it theres four motors and 9 times out of 10 its the one on top of the ac plenum by the defroster vent. Good luck. TIm
 

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I've read that the top one is around $800 at dealer but can be done yourself if you have some know-how and patience. Someone please correct me if I'm wrong.
I have similar problem in that mine will blow cool at times and other times it takes a long time to cool down. Would the low pressure switch cause this or would it be the upper blender motor? Any help would be great!
 

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This happened to me today too. I have an 2004.5 Chevy 2500HD Diesel.

Cold air out of passenger side and hot air out of driver side. I just replaced the alternator yesterday so I have no idea.

I guess I should disconnect the batteries and wait then turn it on without the AC the on. I read that in a previous post but am wondering if it worked for anybody else.

Is there any reason for this? Why does this happen, very frustrating.

Thanks for any advice!!!!
 

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had this happen to me the day i bought my truck. Its a 2005 gmc 2500hd. passenger side blew cold air driver side hot hot air turned the truck off and back on and it fixed its self
 

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Had this happen to me twice each time after I hit a pot hole in the road-- shut it off and restarted it, and all was OK. Hasn't done it in a couple years. :D
 

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There has been much discussion on this in previous threads. Problem is actuator motor that operates heater core door. Parts from dealer is $$$$$ autozone has same for $160, pain to put in but not impossible, dealer quoted $500-800 just do one. There are 4 of these but the flap door is usually the one that causes this problem. Motor can come and go for some time (buddies truck) or just go out like it did on mine. Good luck.
 

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Biotec, so if I were to put a shut-off valve on my heater core hose going into the firewall and keep it closed I would know if that was the problem or not??? AND if that's it is this the motor that is under the dash top right side??? I am assuming that it is working in the am and then sticking open part way later and every once in a while shutting.
 

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Ok i have an 04 CCSB LB7 4x4 gmc duramax. 2 weeks ago the air start blowing warm. I took it to my local shop and the mechanic replaced the low pressure switch, charged me $37. yesterday I get in it and the passenger side is blowing ice cold and the drivers side is blowing very hot. Any help would be appreciated. thanks,
Driver side blowing hot is temp actuator just above transmission hump. Drop the lower plastic shroud on the a/c unit (four screws 7mm socket)
Now unplug the connector at the actuator and remove actuator using a 5.5 mm socket,not a misprint...5.5mm socket. Pull actuator straight down, relpacement is part# 89018365 for most trucks. $119 at GM parts direct on line, that's the best deal I found. If the right side ever goes out, that is a royal pain to replace, have to pull the dash and get under the vent/defrost supply....uses same part#. I just pulled mine out took the actuator apart (4 screws), reset to hold flap in cool mode and put it back in, but did not connect control wire. This gives cold air until new part arrives and I have time to put it in.
Clamping off heater hose only gives luke warm to cool air not cold. You have to have the door shut to get cold air.

Good luck.
 

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Low side pressure of 75-100 with the a/c shut off is normal. It should be the same on the high side with the unit off. Running the low side pressure should be about 10-30 and the high side about 175-225. This would be at high idle. The pressures are dependent on ambiet temps, type of compressor, and whether the engine fan is turning and pulling air over the condensor. I assume you have a constant drive fan with a viscous clutch. Not all systems do. 75-100 on the lowside with the a/c running is probably the result of a serious overcharge. The only proper way to recharge a system is to evacuate it and recharge by weight. Adding charge using gauges is acceptable if you know what pressures to look for. The ones I gave you are general. Whether the a/c is running or not, the pressures will vary based on ambient temperature.
 

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LFingar is correct-- steering you in the right direction

With the air conditioner running, feel the accumulator-- (Large round cylinder tank on the passenger firewall, next to the fuel filter) If the system is working properly, the bottom part of the cylinder should be very cold. If it is not cold-- you either have a plugged system, bad compressor or low/high freon charge.
 

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I had the same problem in my wife's 05 Tahoe, it is the bypass door and there is more than one but if you utube it there are plenty of explanations. Also don't by the cheap ones, I went threw two autozone ones in less than a year then got an ac delco at the dealership, it was a lot more expensive but hasn't failed.
 
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