i have a 1986 928 euro with about 50,000 miles on it (73,000 km)
currently the a/c does not work - however the car only blows hot air out of the dash vents. i can get it to switch to defrost but not anywhere else. on the furthest left or cool setting it blows fractionally less hot but not much.
i put a vacuum pump on the check outlet by the brake booster and it showed no loss in pressure, until i turned on the ignition. i should add that the cruise control engages but does not hold speed. the heater valve at the back of the engine functions when manually operated with the vacuum pump, but appears to always stay open when car is running. i am at loss of what to check next. could it be a vacuum leak, or is my heater/a/c control unit shot? any help would be appreciated.

 

It sure sounds like a vacuum leak to me. Or low vacuum being applied.

Here's a simple one: check the operation of the one-way valve that is installed by the brake booster. It's a short cylinder maybe 1 inch across with lines attached on either end. Mine's blue/black. These can get plugged and sticky and prevent adequate air flow so a small leak prevents a good vacuum from being drawn.

Unfortunately, the real answer likely lies befind the console. Archives are full of info on that because it is so common.

 

It definitely sounds like a vacuum leak. The procedure for testing can be found here:

http://members.rennlist.com/pirtle/svc_act.html

 

I think you may have two problems. Vacuum leaks and no cold air. I have been through these problems with both my 928's. As mentioned you can search the archives for information. Go to the bottom right of the rennlist forum page and use the "search this form" box. Try Vacuum leaks or hvac system. Your control unit is probably ok. If you need help to fix I am in Saskatoon. You can call me 306-242-3535 or email me daryllmiller@hotmail.com.
Good Luck
Daryl Miller

 

thanks for the info. i have tested all vacuum lines and they seem to all hold a vacuum. i have to get a partner to check the actuater arms while i apply vacuum. the temperature servo motor (right under the dash pod works. well back to the drawing board.
Gord Callaghan
1986.5 928 euro

 

I am going from memory so I may update this after I look at my car. I understood you lost vacuum when you turned the key on. From under the hood find the vacuum line that goes to the heater control unit in the car. It is connected to other vacuum lines near the brake booster. Hook your vacuum pump directly to this line. We are bypassing all the other vacuum systems and concentrating on the heater/air systems. Does it hold vacuum? If yes turn the heater control to defrost and the temp to cold. Turn the key on. Check to see if it still holds vacuum and the heater valve is now closed. IF yes turn the heater to bi/level. Does it hold vacuum? Remember to have the key in the on position. Try in all positions to see if it holds vacuum. Let me know what the results are and we will go from there.
Daryl