Rear A/C not cooling, actuator is fine

SepticFuddy

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I just replaced the front evaporator in my '04 5.4L with rear climate control, vacuum tested the system and recharged it. However, it would only take the amount of refrigerant required for a front only unit (32 oz.) instead of the full 54 oz. for a front and rear unit. The front A/C is blowing cold just great, and the rear A/C isn't blowing cold at all. I know the blend door actuator and rear climate control panels are not the issue because I replaced the gear in the blend door actuator and turning the controls to heat puts out heated air, while turning back to cool puts out ambient temperature air. It seems as if the rear refrigerant lines are somehow blocked off from the rest of the system, but in pouring through the service manual I found, I can't find anything that would explain how that might be.

Can anyone explain what might be happening/how to diagnose the issue? Thanks.
 

Hamfisted

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Feel the refrigerant lines under the Expy there at the rear AC area. See if one is cold with the AC compressor running. If one of the two lines is cold the rear expansion valve could be stuck closed. You'll have to pull the right rear interior panel off to get to the expansion valve for further examination and possible replacement.
 

SepticFuddy

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When I pulled off the panel to check, one was cold going all the way through the rear TXV to the rear evaporator, and it accepted the rest of the refrigerant I'd bought for the 54 oz. It's hard to say for certain whether it was blowing cold or not since it was a cool morning when I checked it, but it's hard to imagine it wasn't if the line was cold. The next time I tried running rear A/C, it was blowing hot again. I'm a little confused. Maybe the recent heat wave has something to do with triggering the problem? And maybe since my vacuum test was done in the heat and it only took 32oz. afterwards, the rear part of the system didn't actually go under vacuum?
 

Dennis_H

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I'm not sure about the config on these units, but I had a full size van that I thought was having the same issue. Turns out the air passes through the evap of the AC then the heater core. The heater was still getting water through it and heating up the air after it was cooled. Fixed the hot water cut off valve (and put a manual cut off in line just to be sure) and it was fine. Maybe that could be the issue?
 

Motorcity muscle

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Not sure what the problem is but if system was under vacuum there is nothing to block the suction line, so whole system got evacuated. Must be some type of valve in the liquid line besides expansion valve, that would be the first thing to check, TXV's are mechanical and rarely fail.
 

SepticFuddy

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I'm not sure about the config on these units, but I had a full size van that I thought was having the same issue. Turns out the air passes through the evap of the AC then the heater core. The heater was still getting water through it and heating up the air after it was cooled. Fixed the hot water cut off valve (and put a manual cut off in line just to be sure) and it was fine. Maybe that could be the issue?
This one has a blend door that picks a route between evap + heater core and just evap, which I already fixed the actuator on. I can feel it get hot when it runs the heater core route and ambient temp under cool, so it's definitely not that.
Not sure what the problem is but if system was under vacuum there is nothing to block the suction line, so whole system got evacuated. Must be some type of valve in the liquid line besides expansion valve, that would be the first thing to check, TXV's are mechanical and rarely fail.
That's what I was thinking but for the life of me I can't find any sign of such a thing between inspecting manually and pouring through the service manual I've got.

EDIT: Went for a drive today and it seemed to be working. 70s outside most of the day, lower 80s when I checked it at the end.
 
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Motorcity muscle

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If it works sometimes, I would lean towards the blend door sticking. When it is not working check the two rear a/c lines, larger line should be cold and smaller liquid line should be warm to hot depending on outdoor temperature.
 

SepticFuddy

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It's definitely not the blend door, since I fixed both of them just before the original post
 

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