Inconsistent air conditioning after refresh
On my recent roadtrip in my 88 S4 with rear AC from Portland àSpokane àPortland I noticed some inconsistent cooling in my air conditioning system. The symptoms are it will blow very cold for a while and then blow cool to warm and then cold. This cycle will take about 10min.
If I turn off the AC and turn it on after a few minutes, I get cold again. The problem seems to get worse at the outside temp goes up. A couple other observations: the problem is worse if I don’t use the rear AC. I get really cold air if the car has not been driven for a while. I get more consistent cooling not in direct sunlight. Any thoughts? - My initial thought was the evaporator is freezing/thawing because of the cold/warm cycling. But I am not familiar with the symptoms. - When I had the system serviced, I don’t think the tech turned on the rear AC (opened the solenoid) when they ran the service, could that have affected the evac/charge? Background on tests and recent work:
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Icing of the evaporator,
35c vent air _IS_ admirable, but in high humidity environments you will develop ice more than in lower ones. My car will ice up on a drive thru SanFran in evenings in the foggy districts...but when I climb above the fog, its gone. You can...adjust this, shoot for a few more degrees at the vent..35d vent suggests a 20d evaporator. |
Relay in the head unit may be going south- most of them are past their sell by date now. Mine was doing something similar albeit somewhat hotter over here.
If that is the case the possible solutions are a rebuilt unit, change out the relay yourself or possibly use the signal to trigger an extra relay with a fused power supply from the hot post to the compressor solenoid. |
Originally Posted by FredR
(Post 15013960)
Relay in the head unit may be going south- most of them are past their sell by date now. Mine was doing something similar albeit somewhat hotter over here.
If that is the case the possible solutions are a rebuilt unit, change out the relay yourself or possibly use the signal to trigger an extra relay with a fused power supply from the hot post to the compressor solenoid. |
Originally Posted by Speedtoys
(Post 15013950)
Icing of the evaporator,
35c vent air _IS_ admirable, but in high humidity environments you will develop ice more than in lower ones. My car will ice up on a drive thru SanFran in evenings in the foggy districts...but when I climb above the fog, its gone. You can...adjust this, shoot for a few more degrees at the vent..35d vent suggests a 20d evaporator. |
That problem is a bad antifreeze switch. You can adjust them but it is usually futile.
Replace the anti freeze switch. |
Originally Posted by Earl Gillstrom
(Post 15015930)
That problem is a bad antifreeze switch. You can adjust them but it is usually futile.
Replace the anti freeze switch. Good luck, Dave |
Originally Posted by j.kenzie@sbcglobal.net
(Post 15017934)
Yep. I've had the same thing. If you park it after it's been poorly functioning, you should find a big puddle beneath the car as the evaporator defrosts.
Good luck, Dave Totally normal in many conditions, |
Originally Posted by Speedtoys
(Post 15018149)
that could just be a good working AC system.
Totally normal in many conditions, Dave |
Originally Posted by Earl Gillstrom
(Post 15015930)
That problem is a bad antifreeze switch. You can adjust them but it is usually futile.
Replace the anti freeze switch. |
the freeze switch failed in my 88 S4,
the same symptoms as what the OP reported were also going on in my car, a new freeze switch and its working fine now. The WSM says they can be adjusted , but IMHO its better to just swap in a new part |
Is there any way to bench rest the temp switch? |
Put an ohmmeter on the contacts. It should read 0 ohms. Put the sensor in ice with a little water. It should read infinity in less than a minute.
Remove from water and it should go back to 0 ohms in a few seconds. |
Exellent thanks👍 |
Originally Posted by Earl Gillstrom
(Post 15021533)
Put an ohmmeter on the contacts. It should read 0 ohms. Put the sensor in ice with a little water. It should read infinity in less than a minute.
Remove from water and it should go back to 0 ohms in a few seconds. Is there one for the rear ac too? I didn’t see one in pet EDIT, after thinking about it I realized the freezer was colder than 32-degrees. So I decided to adjust the switch. Turns out the capillary tube/probe was fine. The switch was just triggering at 29-degrees. I was able to adjust it to trigger at 33-degrees.https://cimg6.ibsrv.net/gimg/rennlis...0ba4406a45.jpg |
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