# Suburban 2017 front ac not working rear fine



## socrates777usa (Oct 20, 2019)

I have a 2017 Suburban that has an odd AC issue that a mechanic has tried to resolve twice and the issue is still happening. 

Symptom:
After driving in the Suburban on the highway for approx 20 minutes the front air pressure drops to a trickle, but the rear air works normally. I can still feel ice cold air coming out of vents but the air pressure so low that the cold air falls straight to the floor. The pressure would not move a piece of tissue paper placed in front of the vent. Defrost position does not work either. 

Changing fan speeds, temp, position or using recirculating air vs fresh air has no affect. Turning system off and on from 1- 5 minutes does not affect it either. 

After parking at destination and letting the truck sit for at least an hour, the front air works normally again until driving for another 20 minutes, then it fails again. 

What has been tried:

The mechanic changed the blower and the "resister" component. Has seen the truck twice. 

My thoughts:

I am starting to think that the system might be freezing up due to a Freon leak, but I can't explain why the rear air works. 

I also thought the actuator my been broken, but I can't explain why it works for a time and then stops instead of not working constantly. 


Any help here is much appreciated. I have been living with this in the Texas heat for about 2 months now.


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## chandler48 (Jun 5, 2017)

IMO, it is freezing up. When it happens, open the hood and look at the piping going through the firewall. It may be freezing there, or in the core. As you are driving and this happens, increase the heat setting to see if it will melt off and restore the AC. Have the R 134 checked to make sure you have the proper amount. It could be over charged.


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## Porsche986S (Dec 10, 2017)

Has your mechanic put a set of gauges on the vehicle and monitored the pressures ? That is the correct way to know if the system is under or over charged . There are pressure/temperature charts to know what the low and high side pressures should be for a given outside ambient temperature . As an example the pressures will read differently at 70 degrees vs. 80 degrees . As a baseline for diagnostics you need to know that the amount of refrigerant in the system is within factory specs . If the level is correct and within specs THEN you can start with figuring out one by one which component is failing .


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## ukrkoz (Dec 31, 2010)

So whatever happens under the hood has little influence on what is inside the cabin, because you have AC core inside the dash, and from that on, blower blows air stream at it and blander doors direct it to the front and to the rear. 

As the rear airflow is working fine, ducting from the AC core to there is ok. Blander door that directs air flow there is ok. Blower is OK, as I do not believe you have TWO blowers, one for front and one for rear. Same points out that AC is working fine from the AC radiator all the way back to the AC core.
That leaves you with area concentrated on between the AC core and front vents.
My thoughts are like this:
1. blander door actuators for the front slowly give, allowing doors to almost close. Not sure, if you have pneumatic or electric ones, that's for you to determine.... As you let vehicle sit, something cools down/resets itself, and it goes back to normal. For the year, it's likely bunch of electric actuators prone to failure, as usual with GM electronics.
2. climate control gets monkey brain and lets those front doors to slowly almost close.
As curiosity, find out if you have auxiliary blower for the rear, though I doubt. Too expensive and GM is bunch of misers. 

Besides, 2017 and out of warranty?


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## chandler48 (Jun 5, 2017)

@ukrkoz has a good point. Blend doors could be losing vacuum and malfunctioning, due to hose cracks or a bad directional switch on the dash.

My Dodge Ram uses a vacuum pump since a diesel is a positive pressure engine, and it only operates the blend doors and 4wd. With the Suburban, I'd check for vacuum at the directional switch.


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## ukrkoz (Dec 31, 2010)

Under the dash space gets VERY hot. Head unit itself produces ton of heat. It is very easy for a seal or line to go bad in such environment.


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