Tim Emsky

Assistance Please: I have a condition of FULL heat regardless of control settings, and have gone through most of the posted tests on Rennlist without success.
The A/C would only blow cool (not cold) air this spring, so I had the system bled and recharged. Nice cold air for about two weeks, then a dramatic shift to blast furnace air, no matter what the settings are at.
I found that the heater valve is in the OPEN position in every position with the exception of all systems OFF or with the A/C button depressed. (still hot air)

So...here's what I've tested and changed so far:

1. Replaced heater valve, in CASE it was leaking. (it was not)
2. Tested sensor circuit; outside sensor has 550 ohms in ambient temperature, and will slowly go down to approximately 450 ohms when heated. Seems to work. I even tried replacing it with a 1200 ohm resistor, but the condition persists.
3. A/C compressor clutch does engage
4. tested vaccum at the T, and have 25 lbs. at idle. Tested all four lines, and all hold vacuum.
5. Tested all vacuum pots inside the car, and found that the yellow line (floor vent) is gone. Also found that the orange (center vent) is gone.
6. SO, I plugged off the bad vacuum lines to eliminate the vacuum leak in the system, but the heater valve still stays open in every position other than OFF or with the A/C switch turned on.

Even with the heater valve turned off, the air is still quite warm.
What am I missing here? Could it be the interior temperature sensor?
Also, I noticed a few bubbles in the A/C glass window. So the tech either did not fill the system to full spec's, or I have a LEAK. Any suggestions on how to spot a leak in the system? All fittings look dry.

Thanks in advance for any suggestions!
Tim

ROG100

Tim,
What MY of car?
These are my "off the top of my head" thoughts" : -
1) Is the heater valve fitted in the right direction for flow - arrow on the valve.
When you apply vacuum do you see it move?
2) Recirc flap, blue line - when you apply vacuum can you hear/see it move - under the glove box - get under with a flashlight and have a look. It could be letting ambient air in all the time.
3) If the A/C compressor engages that tells me you have some pressure in the system.
4) Quick way to see if the inside sensor is working. Put your hand over the sensor grille - blocking off any air to it - temp from A/C should fall. If not refer to the WSM as there is an electrical test for that as per the outside one.
Good luck.
Roger

Tim Emsky

hi Roger, forgot to post the MY; it is an 88 S4
Yes, I ensured that the heater valve was placed in the correct direction, and it does function WHEN it has vacuum applied to it. (only when the AC button is on, or if the heater controls are off.
I will check the recirculating flap for movement on the blue line, but the actuator holds vacuum.
Does the inside air sensor blow air through the grill or draw it in? I don't seem to have any air movement through it. Could this sensor be causing this havoc?
Do you know if there is a source for replacement rubber bladders for the vacuum pots, or is it necessary to purchase the complete units?
Tim

Alan

Tim,
Sure sounds like the head unit may be fried - can you swap with someones equiv year locally? (or at least try yours in their which has less risk for their unit...).

First though make sure all the connections are good... its easy to remove from the console to check.

Alan

ROG100

Tim,
The unit sucks air - light a match and see if it sucks the smoke in - please do not set your self or the car on fire.
Follow Alans sage advice he is the electric guru bar non.
In the WSM there is a test for all the HVAC electrics and as long as you have an ohmmeter you can check everything. I did and I'm electrically challenged.

Tim Emsky

Roger, I will see if there is any air movement from the sensor; thanks
Alan, I am in the frozen north. There is ONE other 928 locally (within 500 miles), but the owner would not be willing to have me remove his head unit for a "test". Is there a suitable test for the head unit to verify if it is functional?
Tim

the flyin' scotsman

Tim.........where exactly are you? I'm in the Crowsnest Pass area; East of Sparwood and Fernie et al.

Tim Emsky

Malcolm, I'm in Prince George

the flyin' scotsman

A little far for hands on assist. If your sure that the water valve is closing on a few of the control head setting then that would indicate that vaccum does get to the valve and it operates. The problem would then be the head itself.

Do the trick of tying the water valve closed; no heat at all which will give you time to R&R the head to clean it and the connectors. If that doesn't work then you may need a replacement head; someone on the List rebuilds them just don't remember who.

Intrinsicate

I always tie off my water-valve in the spring, and I have reliable ice-cold a/c throughout the Vegas summer - not only reliable, but instant after start-up.

Ron_H

If it is the head unit, there is a thread dealing with how to install a new internal relay (what goes bad). I did it and I am in Roger's catagory. I have trougle spelling eletreekal. Amazingly it worked. You will end up with an extenal relay attached to the head unit and can then reinstall the head unit into the dash and forget about it. Requires soldering.

Alan

Ron,
That relay drives the AC Compressor clutch right? that doesn't seem the likely issue here (although agreed its a common enough one...) given that the heat here seems to be water valve related... not lack of AC.

Speaking of AC - just today got my car fixed by Dan @ Exotic - my second original radiator fan went out just 4 months after I replaced the first one (should have just changed both I guess). So lifetime on these is about 12 years or so (probably rather less in Phoenix).

I can tell you that loosing AC here in August is no joke - its not like rolling the windows down helps AT ALL... Its all you can do not to pass out - no joke

Alan

Ron_H

If he is getting a costant blast of hot air, it would seem to be the heater valve. But he checked it. I also have a stick stuck up the flap under the passenger side parcel tray to keep the interior air recirculating rather than allow outside air in. Maybe he has a similar problem.(?) Obviously, I have a vacuum issue, but have not bothered to track it down yet.

Tim Emsky

Consider the heater valve wired shut. Isn't the relay on the head unit strictly to run power to the AC compressor clutch?
I do have a problem wth the floor vent vacuum pot, but the recirculating vent seems to be operating.
Does the head unit have any other electronics that can go bad?

bd0nalds0n

The decision/logic to close the heater valve is actually made by the mixing motor, which is located under the dash pod. I went through the same process of trying to find out why my heater valve wouldn't shut no matter where the temp slider was. You might want to swap with a known good used unit first. It's quick and a lot cheaper than a rebuilt climate control head.