StanE_86.5

I have been trying to track down why my AC only blows hot. Already replaced both inside and outside temp sensors. Finally started checking resistance per postings and found that the resistance across the yellow leads from the control head does not change when the temp slide control is moved. The posting I found says to next remove the control head and do some checking on that.

I have looked up postings on how to remove the head and they say to pull the h shaped grill out and remove the screws. I don't see any screws. Is the only way to pull the entire center console out and get to it from behind? I have the radio out and both side panels removed.

Any advise will be appreciated.

Dozman

Stan,

1.First remove the discharge air grill above the a/c unit
2.Remove the 'H' like trim piece (The trim piece is the small thin plastic piece that surrounds the radio, a/c unit, and the ! module), This is a very thin piece of plastic be sure not to break it. I found it very helpfull to remove with very thin screw drivers. Work it slowly out. As you do it will flex here and there and snap out.
3.When removed this will reveal screws that retain the a/c unit (4 phillip head screws) and your ! light reset and seat lock button module (2 phillip head screws).
4. remove the ! unit, then remove the a/c unit.
5.Proceed with your diagnoises.

I would try and ohm out your interior and exterior temp sensors before trying to diagnois the problem further. If my memory serves me correctly, the 2 sensors work in series with each other. If one does not work, then the total resistance is off for that circuit and the temp control will not work correctly.

Interior temp sensor is behind the small 1-1.5" round grill in the center console, exterior temp sensor is located in the alternator cooling hose (Left front corner of car, accesible through the left headlight when it is removed and in the down position.

Check Nichol's site for write up.

dr bob

Exterior sensor is in the cooling hose that attaches to the front (front is front of car...) of the forward wheelhouse liner piece. There's a metal bracket that hols the hose in an upside-down "U" configuration there (keeps the rain out I guess) and the sensor is wired to a plug on that same panel.

I don't know how easy it is to pull a headlight assembly. Taking the wheelhouse liner panel out takes a few minutes after the car is raised and the LF wheel is removed. Plenty of room to work in there, maybe better than trying to do brain surgery through the headlight hole in the fender.

HTH!

atb

Just to add to John's comments:

I wasn't able to pull the HVAC unit out without disconnecting the wires to it. The only way for me to access them was to remove the driver's side cover on the console. There is a screw back by rear lower corner of the panel. The front seat needs to be in the full "low" position to get access with a screw driver. There is screw near the front along the bottom edge, and then a third at the front edge of the panel. Once these are removed, slide the panel straight back. The front part has a slit that will work its way free. Once out, the wires behind the console to the HVAC unit can be accessed. These are on the driver side of the unit, and pull straight out, I don't recall there being any clips or clasps.

-Adam B.
'88 S4

-Adam

StanE_86.5

Thanks, John. When I read earlier postings I kept thinking the H shape piece of plastic they referred to was the vent grill. YOur discription was what I needed. I got the control unit out last night and (unfortunately) it tested OK. That means I have a break in the wire somewhere. I have already replaced and double checked both inside and outside temp sensors. Now I have to track down a short somewhere. This is getting tedious.

Dozman

I can't find Wally's write up on the HVAC system, that he sent me months ago. You might want to ask him for it.