SOLVED! No rear A/C ?

linneje

Original poster
Member
Apr 26, 2012
404
The front A/C works great. The rear A/C did have a bad actuator (blend door). Verified that it was bad visually (would not respond to commands nor recalibrate) and with a scan tool. Removed bad actuator. Was able to move the blend door with my fingers (it springs back when released), could hear it open and close. Installed new actuator. Visually watched it respond to commands.

Rear A/C however is not cold. It is warm. Verified by sitting back and using rear control. Air does not get cold even though the blend door is controlled by the actuator.

What could be causing this? If it were leaking, why would I have A/C in the front? I have been using the front A/C all year.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
There are two actuators. Is it possible you replaced the mode actuator?

rearactuators-orig.jpg


In the above image, there is #3 which is the mode actuator and #33 is the temp actuator.
 
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linneje

Original poster
Member
Apr 26, 2012
404
Good thought, but no. When I originally had the problem, I took the side panel off, worked the rear controls and verified that the mode actuator would successfully shift air from floor to face and back again. That actuator sits on top of the assembly.

The actuator that was not working was to the rear of the vehicle, and kind of sits on the side of the assembly. That is the temperature actuator. I had watched it, and it was unresponsive to any requests. I also verified with a scan tool I had borrowed, it shows you the commanded position and the current position of the actuator.

When I replaced that actuator I could see it move according to the command from the rear controls. Unfortunately I don't have that scan tool - it could give me more information. But both actuators were working when I put the side panel back on. However, I cannot get cold air even when commanded for cold from the rear control.

I don't understand the rear system well enough to decide what is going on. Shouldn't the refrigerant circulate through the rear evaporator? If the rear evaporator is shot, shouldn't the refrigerant leak out and I would have lost my front A/C long ago?

Full disclosure, probably 8 years ago I had a leak on the back lines and they were fixed with a patch kit. We discussed blocking off the rear with the repair shop, but decided against it.
 
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Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Same as the front, the rear evaporator works whenever the compressor is working. Did you try to feel the lines that go under the rear of the truck into the evaporator? IIRC, there is an expansion valve for the rear evap so if the low pressure line is not cold, that could be the problem.

What does it do when you set it to heat?
 

aaserv

Member
Dec 1, 2019
408
N of Baton Rouge, La.
Id want to verify the evap is getting cold. Like moose said cking for cold line or possibly getting a thermometer to the coil. Maybe run it long enough and see if any evap water runs out the drain. If no air is blowing across the coil it should freeze up and thaw out immediately after you shut it down. Ck it maybe 5 mins after shutting it off and see if water is dripping out the drain line. Be a big coincidence if it has nothing to do with the actuators but s*** happens
Wouldnt hurt to ck the refrigerant. I guess if it was low it might possibly not be filling the rear evap but still have enough to blow cool in the front. When mine was low only the front passenger side blew cold. drivers side and rear blew reg temperature. Once full it blows cold all around...
 

linneje

Original poster
Member
Apr 26, 2012
404
Thanks for the ideas. Rear lines (I went underneath and felt) are not cold. At all. No water running off the drain in the back. So I do not think the rear evap is getting cold. Probably down to checking refrigerant or problem with the expansion valve. I think that is part 18 on the diagram. No idea how to check that valve, or how to get at it, so I should troubleshoot that last.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON

linneje

Original poster
Member
Apr 26, 2012
404
I think that I remember noticing that it was working a couple weeks ago, but I will give the fan clutch another check too.
 

linneje

Original poster
Member
Apr 26, 2012
404
Disappointed. The scan tool that I borrowed gives me lots of information on the HVAC system for my newer vehicles, but for my Envoy very little is given. I cannot get the pressure readings from the scan tool.

In any case, summer is almost over and our camping days are finished (when people ride in the back and use the air conditioning). Makes no sense to fix it now, I will wait until next spring to tackle this problem.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
Well, I think we can narrow your search down a bit. You said in your OP that the front works great, but the rear doesnt work at all. You checked the AC lines running to the rear when the truck is operating with the AC on, and verified that the lines are not getting cold. Now if it was low on freon, both systems (front and rear) would be affected as they are one and the same.

Using this information, either you have a block in one of the lines going to the rear, or the expansion valve is stuck. There are other possibilities, but this is what my money is on.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Just out of curiosity, did you check the pressures with a set of gauges? Not knowing how expansion valve systems work, is it possible that if it was low that the rear may not have enough to run properly but can still cool the front? Maybe because of the long run, if it's low, maybe the rear is just too far to stay cold but the front can. Orifice systems can sometimes still work if low on refrigerant.
 

linneje

Original poster
Member
Apr 26, 2012
404
No I did not. I don't have a set of gauges. I may be able to borrow when I get back to work. Your suspicion is mine as well, perhaps the pressure is enough for the front but not for the back.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
I would disagree. It follows the path of least resistance. But a set of guages is still a good idea.
 

linneje

Original poster
Member
Apr 26, 2012
404
I realized that I didn't follow up on this old thread. So this summer I finally dug back into the rear A/C. Previously, I had a bad actuator in the back, but when I tested the A/C at the back it did not blow cold. Of course, I was at idle. Never even thought.

This summer, my son was sitting in the back on a drive and I tested it. It was actually working. It just needed to get the pressure up to get it cold back there. I had an expansion valve ready to put in, but thankfully I won't be needing it. I guess it is one big loop, but you need to get the pressure up in the rear to get it working. The actuator was the only culprit all along.
 

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