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Discussion Starter #1
The rear AC in my 95 suburban is very consistent. 55 degrees at idle, almost 50 while driving.
The front will fluctuate from lower 50s all the way up to 70. I can't find any pattern to it. Sometimes it feels great, then it feels like the AC was turned off. Even when the front goes to 70, the rear is still blowing cold. All measured with an infrared thermometer.

I'm no AC expert so help would be appreciated. There is only one compressor, correct? So the compressor is fine since the rear always blows cold. Could it be the blend door is moving sometimes?

I did take it to an AC shop. The pressures where fine and the front was blowing cold while they had it, so they just said it works.

Any thoughts?


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What was the outside temp? The test of an AC system is temperature differential, outside temp vs output temp. Is it putting out the same temp front and rear?

I know on my burb it takes 10 miles or so with front and rear AC to get it cooled down and then it will freeze you out at the 20 mile mark.

Yes, one compressor but the front has an orifice tube and the rear has an expansion valve. I have had the orifice tube clog up while the rear works great. Then the front works great while the rear doesn't.

On a 95 burb the orifice tube is found on the passenger side of the engine bay just after the "Y" split located behind the condenser. One side of the "Y" works the front and the other flows to the back where the expansion valve is located.

To answer your question, "Can an orifice tube work intermittently?" Not really. You could have debris in the system that catches in the orifice tube. I had this on my burb, took forever to flush it all out.

I recommend you check into your cooling stack and make sure the condenser is super clean and the space between condenser and radiator. This can also help with coolant temps. It is also a good idea to look at the evaporator coils as well.

If the coils check out do you have an issue with your HVAC and door control. Usually it just fails.

Just a guess, you have debris in the system and it clogged up the orifice tube. Be very careful, I had this with mine when a compressor died. I could get the front working and the back suffered or I could get the back working and the front sucked as debris moved throughout the system. I finally had enough and spent hours flushing the entire system. Crappy work and it sucks. After all this you must vac the system down and remove all water. Fill with proper amount of PAG oil then add freon.

Be careful of the freon you add to the system as most on shelf stuff has an ounce of oil in it. Ask the parts guys for freon without oil, usually it is not on the shelf as it is just a bit cheaper. This, if not planned for will put too much oil in your system and cooling will suffer.

Start with the cheap, check the coils and blend doors.

My 2 cents,

Brian
 

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x2 bshull
The diesels do not have a heater coolant shutoff valve, although the gas shutoff valve only slows it down.
I put a brass shutoff ball valve on the heater hose to keep the heat out of the cab.
Every degree counts here.
Also make sure your recirc door is closing and there is no debris for it to hang up on.
Are you getting good air flow out the dash vents? Does it slow down when the temp rises?
 

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Whistle Pigs Are Cool
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Also make sure your recirc door is closing and there is no debris for it to hang up on.
Are you getting good air flow out the dash vents? Does it slow down when the temp rises?
Would look there first
 

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My 95 truck will freeze the ac grid in the cab and will loose cooling. Its a odd thing to get hot while the compressor is on turn it off and get froze out of the cab.
 

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Yup... Orifice tube debris from a failing R4 compressor... Reclaim the refrigerant, pull the tube out and inspect. If it's got black or gray gunk on it, plan on replacing the compressor and the condenser. If it's clean, pull the condenser and look for leaves and gunk in it.
 

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Discussion Starter #8
What was the outside temp?
mid 90's

Is it putting out the same temp front and rear?
Even when the front goes to 70, the rear is still blowing cold. All measured with an infrared thermometer.
I recommend you check into your cooling stack and make sure the condenser is super clean and the space between condenser and radiator. This can also help with coolant temps.
I'll check it out, but since the rear AC always blows cold, I wouldn't think this would be the problem.

I put a brass shutoff ball valve on the heater hose to keep the heat out of the cab.
Every degree counts here.
Also make sure your recirc door is closing and there is no debris for it to hang up on.
Are you getting good air flow out the dash vents? Does it slow down when the temp rises?
I like the brass shutoff idea as an extra. I'll check the recirc door, but I would assume that it fully closes since the front does cool down into the lower 50's. Perhaps the recirc door is opening, or heat blend door is opening, and then later closing. Air flow is always strong. When the temp rises, you don't notice anything change other than warmer air. Feels exactly as if the compressor stopped, except it hasn't and the rear stays cold.

I guess I'll take it back to an AC shop and explain better what it does, mention the orifice tube debris and see where it leads. Thanks guys
 

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With credit to previous posters:
The rear air is working good so there is nothing wrong with the freon cycle. If there were trash on the OT then it would also plug up the expansion valve on the rear air, it has an even finer screen than the OT.
I have never seen an intermittently blocked OT but anything is possible. Having owned more burbs than anyone should be allowed, I can sympathize with you.
With it running and a/c on max/recirc, pull the blower fuse and see if the accum/dryer freezes up. If it does, then the problem is a door, solenoid, wiring, or the control head.
 

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My 95 truck will freeze the ac grid in the cab and will loose cooling. Its a odd thing to get hot while the compressor is on turn it off and get froze out of the cab.
Usually, the low pressure switch on the dryer is out.
This switch is commonly failed due to location.
Fortunately, changing it is just a matter of screwing in and out without leaking any refrigerant.
Plus the switch is cheap.

Try this first and see.
 

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Discussion Starter #11
Here's a new twist. This morning the AC compressor didn't engage. Messed with the dash switches, messed with wiring under hood, nothing. I was driving around town with the windows down and both blowers full blast. After around 20 minutes of driving the compressor kicked on. Stayed on the rest of the day, cooling the rear and the front doing its thing up and down.


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My guess is you're low on refrigerant. Not enough system pressure to close the low pressure switch when cold. As things warm, refrigerant pressure rises to where the switch closes allowing the compressor to engage.

Sixto
97 C2500 burb 189K miles
 

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Low on freon will also cause the evap. to freeze up and slow down air flow.
Humidity here is bad.
 

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Could be. Low charge could explain a few things...
Odd the shop found no issues with the pressures...
 

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Discussion Starter #15
Ok, here's the update. The AC clutch stopped engaging before I had a chance to check anything out. I was kind of glad, since the AC shop wouldn't be able to say it was working fine.

They ended up having to trace down a bad wire that caused the compressor to stop. I was hoping that would be the source of the erratic behavior. I don't usually drive the suburban, so when I got it back I took it to work to verify the AC was working.

Felt great for a bit, then temps in the front started rising. After driving it for a few days and paying attention to when it got warm, I realized it was always warm when I was on the highway and fluctuated up and down when I was around town.

Long story short, it's the recirc door actuator. I pulled the blower and the door is partially open. I think at higher speeds the air flow was pushing it open farther. I wedged a screwdriver from the floor up through the vent to hold the door closed, then took a 30 minute drive and froze my butt off.

Now the real problem is how do you access the actuator. It has two screws. The lower screw is accessible, but as much as I tried I can't get at the top screw. I have removed the dash before and I never want to do that again. Anybody know how to access the recirc actuator?


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Take the top one out from the bottom. On my truck im going to have to cut the firewall insulation so I can get the socket on the bolt. Glove box out you cant see the bolt for the AC box.
 

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Discussion Starter #17
Take the top one out from the bottom. On my truck im going to have to cut the firewall insulation so I can get the socket on the bolt. Glove box out you cant see the bolt for the AC box.
I was trying to come from the bottom. I can feel the top screw but not see it and there just doesn't seem to be enough room. I'm thinking the AC box may have to come out to get at it.



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After fighting the same problem you are having I permanently closed the recirc door on my burb and blocked the opening with a block of high density foam.
 

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Discussion Starter #19
After fighting the same problem you are having I permanently closed the recirc door on my burb and blocked the opening with a block of high density foam.

I had an open tube of rtv so I used some when I wedged it closed. Down here in the heat I'm never going to want the door open. We do take trips up north in the winter and I think I'm going to want to be able to open it for defrosting.


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I think it actually made the defrost work better.
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