Guys,

Have done a search and can't seem to get an answer to my questions about the HVAC system and an A/C problem with my '91 964. Help would be greatly appreciated:

1. The AC unit isn't cooling. I figured it was a low freon charge, but the shop checked it and the pressures were as required, so it isn't leaking. The shop did a quick check (didn't have much time as I had to head to VIR), but initially they believe all the major parts are working correctly. So, what should I look at first.

2. Related or not? The cabin fan never turns off. Even at 'Off' it is still running - is this a sign that the CCU is starting to give up after 20 years? Could this be a potential contributing factor to #1?

Thanks,

-Skip

 

If you are talking about the small fan on the back of the CCU it will run for 20 min +/- after the car is shut off.

 

What Jim said, and the 2 cabin fans never turn off as long as the key is ON, when the **** is at 0 they run slowly and increase as you turn the **** to a higher #.

 

Thanks guys, nice to know something else isn't broken.

Now, to figure out the A/C issue, any thoughts on that anyone?

-Skip

 

Expansion valve clogged maybe??

 

Is the compressor actually clutching in and running? Cycling on and off? There's one wire going to the compressor clutch that has a spade connector that sometimes pulls out. If the car has freon and your pumping through your system and your still not getting cooling, it could the expansion valve.

 

Thanks guys - The compressor is turning on and off and seems to be working properly. I'll check the expansion valve out.

-Skip

 

I had a similar problem that ended up being the right and left heat doors leaking. These are the two in the trunk. I believe there are 4 servos in there. They were not closing completely when the CCU **** was on the coldest setting. I adjusted the control rods and now the AC is working better than ever. There was just enought hot air flowing to "dilute" the cold air from the AC.
Gary

 

Based upon this, I think the reference is to the blower fans control on the CCU. Mine has an intermittent issue: full on/full off no matter what setting. Probably a bad pot.

As to cooling... May be the valve or excess heat (as said), or how about the dryer?

 

@OUR11
It might be a faulty final stage regulator causing your on/off problem. The FSR is controlled by the CCU to enable the fans speed to be variable.

@ swftiiii
Feel the suction tubing fitting at the compressor, it should have condensate dripping from it or at least be cold. The air coming from your vents will be at least 10 degrees higher than that. If it's warm air then consider looking into what gr1275 is talking about. Keep cool.

 

I would check your servo motors in the front (under the wipers/valance) The heater mixing servo might not be functioning. This is pretty common in these cars now.

 

Also check that the hot air pipes (16 on the diagram) on the side of the footwell are cold. My servos and valves were OK but one of the pipes was badly connected to the mixing chamber: the dump valve (in the rear wheelwell) was thus getting no conterpressure and letting hot air heat the mixing chamber.

 

After seeing the drawing above, a somewhat related question: Where does the cabin air exit the car? I found the small flapper boxes behind the rear interior panels, next to the seat belt retractors (removed during my DAS bar install). These allow the cabin air to exit, and have a rubber flap that apparently prevents foul air (or vermin?) from backing up into the cabin. These mount on the main body sill - but where does the air come out underneath or behind? I wonder if these might be blocked somewhere?

 

Can you provide more detail (Or jsut better search terms) for this issue?

I am getting stunningly hot air into the right footwell at any temp setting on the CCU.

Thanks!

RK

 

Here's some more info

https://rennlist.com/forums/2900675-post17.html