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Rear Air blows hot air only #750067
June 28th 2019 7:21 am
June 28th 2019 7:21 am
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
Just4fun1991 Offline OP
member
Just4fun1991  Offline OP
member
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
Looking for input in trouble shooting rear A/C only blows hot air on a 1991 Chevrolet G20 van Aero conversion. Once fixed, I will then post in “What did you do to your van today” section….


Here is what I know with the A/C.

1. Installed new compressor last year, R134a
2. Charged the system up to 4lbs.
3. Ran OK last summer (worked, but just didn’t have the power/cold of a newer vehicle, I know it’s 28 years old and there have been a few improvements in 28 years, I also understand the van is a large area to cool down on a HOT Iowa day)
4. As of last night, the front blows cold air when the AC is turned on, the rear blows hot air.

Here is the issue and what I don't know

1. The rear AC only blows hot air, at first, I thought the rear needed a little time to cool down
a. Blower works great
Rear air worked last year on the way to “Van Nationals and back”. First time using the rear air this year (last night) would only blow hot air. From reading your posts (I’m not a mechanic, but enjoy a good trouble shooting with a voltmeter) it sounds as if I may have 1 of the following causing my problem.

1. Valve up in engine compartment that is allowing coolant to still flow to rear, thus why rear a/c is blowing hot air.
a. Can a person shut this OFF? If so how?
b. Where is the valve located?
c. Does anyone know if that valve is vacuum operated or DC operated?
2. Could I have a bad “expansion valve” in the rear A/C?
a. If so, how does one test the expansion valve?
I would like to say the issue is #1 but would like anyone’s input before I tear into it this weekend and get soaking wet from the humidity this weekend.

Re: Rear Air blows hot air only [Re: Just4fun1991] #750078
June 28th 2019 4:13 pm
June 28th 2019 4:13 pm
Joined: Sep 2005
Posts: 8,845
Hickory Flat, Jawga
CatFish Offline
carpal tunnel
CatFish  Offline
carpal tunnel
Joined: Sep 2005
Posts: 8,845
Hickory Flat, Jawga
The hot water valve should be a vacuum operation. If it's a separate valve, it was (most likely) teed into the heater lines and the control (vacuum) tubing by the conversion people, If that vacuum line is off you should feel the front heat on as well, at least partially. Or the valve may just be bad.

The TXV (expansion valve) on the rear can be tested by warming it's remote bulb. You will need to locate the bulb and separate it from the return line (usually it's held against the return line by a small clamp or plastic clip and a GOB of dumdum). You should be able to warm it with a rag soaked in hot water or with your hand. They are almost always tough to access.
Once the bulb is warmed the expansion valve should open and allow refrigerant thru the coil. You will be able to feel the return line leaving the coil get frosty.
You didn't say why the old compressor was replaced.
If the old compressor had a mechanical problem, there was trash in the lines or the system was not properly evacuated, the rear TXV may be clogged. They clog very easily. Any moisture not removed from the system will mix with so-called "leak seal" and clog the TXV as well.
The rear coils can have quite a bit of oil "logged" in them. If it was not properly flushed when the system was changed over the residual old oil and the new oil could have made crud which will clog it as well.

Happy hunting. Hopefully it's something simple (and cheap).

BTW We were at Lake Rathbun just last month for a few days.


Last edited by CatFish; June 28th 2019 4:21 pm. Reason: kant spel good
Re: Rear Air blows hot air only [Re: CatFish] #750083
June 28th 2019 7:42 pm
June 28th 2019 7:42 pm
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
Just4fun1991 Offline OP
member
Just4fun1991  Offline OP
member
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
Thank you for the advice!

The compressor was replaced due to a leak. Van was changed over to 134a at that time.

Air worked last year ok. Nothing to brag about working though ...

I will check on the vacuum valve under the hood.
** If vacuum is held to valve, does that allow the coolant to keep flowing to the rear? Next, what controls that vacuum to the valve? Going to assume (I'm good at the assu part) the simple test is pulling off vacuum to valve or pulling vacuum to valve.

As far as I know, last year the rear air worked better than the front air. Doesn't mean it couldn't be clogged or something else this summer.

Lake Rathburn is nice. Somewhat wish there was a place to post when vanners are going to be in the area. I would have driven down to meet you and given you places of interest to at least visit .

Thanks
Bob

Re: Rear Air blows hot air only [Re: Just4fun1991] #750087
June 28th 2019 8:14 pm
June 28th 2019 8:14 pm
Joined: Sep 2005
Posts: 8,845
Hickory Flat, Jawga
CatFish Offline
carpal tunnel
CatFish  Offline
carpal tunnel
Joined: Sep 2005
Posts: 8,845
Hickory Flat, Jawga
Bob, heater valves will default to heat. If they lose vacuum or the diaphragm fails they will open to provide heat in case it's winter time. It's a safety thing.

We stayed at Buck Creek Park for a few days. Pretty little COE park. Explored from Bloomfield northwest to Moravia and west to Promise City. Iowa has some of the best small towns in the USA, sorta like having a time machine...... smile


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