A/C question
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Rest In Peace
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Joined: Jul 2002
Posts: 510
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From: Glen Mills, PA
All previous responses are good. Just a few pointers.
The heater valve is closed by full vacuum. If you have a vacuum leak any place in the system, the heater valve may not be kept closed. A symptom would be extra heat under extra engine load, (low vacuum) such as going up hills. Use a tiewrap to keep it closed while testing.
You can check if the front evaporator and expansion valve is working by feeling the input and output of the evaporator at the expansion valve under the cowl cover. It should be very cold, input and output. At the input of the expansion valve it will be warm. (small pipe).
Be careful with the previous descriptions. The reculation flap is not the comb flap.
The heater valve is closed by full vacuum. If you have a vacuum leak any place in the system, the heater valve may not be kept closed. A symptom would be extra heat under extra engine load, (low vacuum) such as going up hills. Use a tiewrap to keep it closed while testing.
You can check if the front evaporator and expansion valve is working by feeling the input and output of the evaporator at the expansion valve under the cowl cover. It should be very cold, input and output. At the input of the expansion valve it will be warm. (small pipe).
Be careful with the previous descriptions. The reculation flap is not the comb flap.
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Rest In Peace
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Rest In Peace
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Joined: Jul 2002
Posts: 510
Likes: 1
From: Glen Mills, PA
One more comment on the heater valve. If your HVAC is working normally and you stop for lunch, the heater valve opens and fills the heater with hot coolant.
When you restart the engine, you have to cool all that coolant before you get cool air.
To eliminate this problem,Gary Knox and I developed a circumvention. Go to my website:
http://members.rennlist.com/captearlg/
It does depend on a properly working vacuum system.
When you restart the engine, you have to cool all that coolant before you get cool air.
To eliminate this problem,Gary Knox and I developed a circumvention. Go to my website:
http://members.rennlist.com/captearlg/
It does depend on a properly working vacuum system.
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Joined: Apr 2002
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From: Portland, Oregon
Many thanks to those who took the time to respond. I will get a chance to implement some of your suggestions this weekend. I really appreciate all the help.
This list is the best.
This list is the best.
Burning Brakes
Joined: Sep 2003
Posts: 957
Likes: 0
From: North Central Florida (Gainesville) USA
Hello Joe F,
I am having the EXACT same issue with my 1989 s4. I'm hopeful that with the information in Walley P's 928 HVAC FAQ (request copy of it from him) and the information in this thread that I'll be able to tackle the issue. Sometimes I get equally cool air from the CDV as I do from the REAR unit. Most of the time, however, the CDV output is barely cool....at speed on the highway they are equally cool (42F or so). My guess is that the fresh air vent actuator or some other vacuum flap is not working correctly. Should be a reasonably doable repair NOT requiring disassembly of the dash itself. I'm just relieved that cool air is lurking in there somewhere....the system is functional. If anyone wants to help me with the diagnosis at SITM, I would really appreciate it
Thanks in advance. Keep in touch Joe F.
Tim / tuk_928
I am having the EXACT same issue with my 1989 s4. I'm hopeful that with the information in Walley P's 928 HVAC FAQ (request copy of it from him) and the information in this thread that I'll be able to tackle the issue. Sometimes I get equally cool air from the CDV as I do from the REAR unit. Most of the time, however, the CDV output is barely cool....at speed on the highway they are equally cool (42F or so). My guess is that the fresh air vent actuator or some other vacuum flap is not working correctly. Should be a reasonably doable repair NOT requiring disassembly of the dash itself. I'm just relieved that cool air is lurking in there somewhere....the system is functional. If anyone wants to help me with the diagnosis at SITM, I would really appreciate it
Thanks in advance. Keep in touch Joe F.Tim / tuk_928
Rennlist Member
Joined: May 2003
Posts: 74
Likes: 0
From: Atlanta, GA
I've been through this and wrote about it, plus pictures, on my website. It's not a difficult issue but you definitely need a vacuum pump to test. Testing will easily tell you what's wrong vacuum-wise.
Also, it's easy to install the heater valve BACKWARDS !! When I bought my car the PO said the a/c didn't cool well and he had replaced the valve. Turned out he had installed it backwards and it doesn't seal properly like that. This is also on my webpage.
Best of luck. As long as the rear a/c is cool the problem can't be too expensive!!
John Pirtle
87 a/t 164k
http://members.rennlist.com/pirtle
Also, it's easy to install the heater valve BACKWARDS !! When I bought my car the PO said the a/c didn't cool well and he had replaced the valve. Turned out he had installed it backwards and it doesn't seal properly like that. This is also on my webpage.
Best of luck. As long as the rear a/c is cool the problem can't be too expensive!!
John Pirtle
87 a/t 164k
http://members.rennlist.com/pirtle
Drifting
Joined: Apr 2004
Posts: 2,344
Likes: 49
From: tampa
Back to basics first. Do you have a full charge and a clear site glass? Your compressor is probibly the origional and weak. Probibly not capable of producing the correct pressures. After your sure the pressure is there , then start worrying about the rest of the system.
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