imfinlay

Hi all,

I have an '89 S4 Auto, right hand drive (in the UK). I had a "no heat" failure yesterday - of course it was -3 deg C at the time. No vent flaps moved either, so started hunting for vacuum leaks today. I have done the following checks (MityVac used where appropriate):

1. Vacuum OK to the vac reservoir/cruise control. 20in HG holds for ages.
2. Vacuum check valve tested fine
3. Vacuum to flappy fine
4. Vacuum to HVAC (black pipe) drops rapidly.

So, went inside the car....

5. Vacuum to heat control valve fine (it's fairly new anyway) and it's plumbed in the right way
6. Vacuum to orange pipe drops rapidly, others all OK. So, capped off the orange pipe to the comb vent actuator (mental note to order one and enlist my 7-year-old son to replace it)

Right, so now it gets wierd.

Still no heat. All vents not capped move smartly. There's plenty of vaccum being drawn on the black pipe from the engine. However, I noticed that it doesn't matter where I move the heat control, the heat valve stays firmly shut.

7. Removed the white pipe, and got heat. Not mega hot, but fairly warm. Attached the mityvac, pulled some vacuum, temp goes colder. Suspected the solenoid.
8. Swapped the solenoids between the orange and white pipes - no change in behaviour.
9. Checked the voltage to the white pipe solenoid - it stays constant no matter where the temp control is.
10. Took out the HVAC controller head - on the bench the resistance between the last pin and the one located two to the left varies smoothly.

I have no idea what to look for now - I guess I may have low coolant causing the lack of serious heat, but I need some ideas!

Help!

Ian

p.s. for all other RHD owners - the Nichols site shows vacuum pipes coming out the left of the solenoid block. On a RHD car it's out the right side. The "X" connector and check valve are also on the right side, near the brake servo.

Louie928

Hi Ian,
The heat control (coolant control) valve defaults to "open" with no vacuum which is how it should be when the HVAC control unit is calling for heat, or if you have a vacuum leak and there isn't enough to hold it closed. In your tests, step 5, you said the vacuum to the heat control valve is "fine". I didn't understand whether that was full vacuum or no vacuum. The vacuum level at the heat valve should change depending on the position of the temp slider on the control unit. However, on yours it stays shut all the time. Is it mechanically jammed? Can you move the lever on the side of the valve by hand? Those valves are under a fair amount of spring pressure to stay open.

imfinlay

Thanks Louis,

vacuum to the heat valve was full all the time no matter where the temp control was. I removed the white pipe from the solenoid and got some heat. Not mega heat, but warm. When I used the mityvac to apply vacuum to the valve, the heat shut off as expected, and I could see the lever move. Using it as a vacuum gauge, the vacuum from the soleniod was constant.

After I swapped the solenoids there was no difference.

I've had some direct emails on this, and generally speaking thoughts are:

1. Vacuum is OK now with the orange pipe capped off and it's going to be a pain to fix
2. The setting motor may well be mixing ambiend (cold, very) air with the hot.
3. I should feel the pipes into the valve to see if they're as hot as the radiator pipes. Not sure this is too clever....

Any other thoughts?
Ian

IcemanG17

Hmm
Thats an odd one....same problem I had last month, but it was a faulty solenoid....& your isn't....the default for a broken solenoid is to apply vacuum....I'm not sure if power opens (applys vacuum) or closes (no vacuum)....it seems that power closes the valve, but I am not sure? Its possible the setting motor is out of adjustment & maybe the control head is faulty....is there someone nearby you can switch the control head with?

imfinlay

OK - for future searchers, I figured it out. It was the setting motor (HVAC control motor). Mine would move from cold to hot, but not back again. Manually pushing the control rod got heat. I got a used control motor which worked, but was very noisy. Taking it apart (well you do, don't you?) I found the gearbox was dry. Anyway, being lazy, I swapped the main control board into my dead one and all works great, silent, fast and so on. I also confirmed my sensor string is OK.

So thanks to all!

Ian

bfellows

Hi Ian,

Any chance you could cast an eye over this thread and offer any thoughts as I'm still stumped. I'm yet to find an obvious wiring issue.

https://rennlist.com/forums/928-forum/237806-strange-electrical-happening-update-with-pics.html

Cheers

imfinlay

Sure - check your PM.