John Orr

Well, today I pulled the carpeted side panels in the interior, and exposed the vacuum manifold with the five solenoids. By taken off each line, one at a time, I found there was a leak in the yellow line to the footwell air flow flap (minor leak, holds vacuum for about three minutes, but looses vacuum slowely the whole time), and the orange line, to the center comb flap (Major leak, won't hold vacuum at all!!) So, I know I will have to work on the acutators to change them. What I am still confused about is the vacuum solenoids themselves. When I disconect the black line from the brake booster to the manifold, at the manifold, and put my mityvac to it, and draw a full vacuum it holds fine. But as soon as I turn on the key, with all the AC controls in the off position, the system goes to zero vacuum, and I hear a clicking sound at the manifold. I thought the manifold should hold vacuum until I switch on something in the climate control head unit. Do any of you guys know what the procedure is to check the operation of each of the solenoids. I remember seeing a test procedure sometimes ago, but can't remember where. Or, am I missing something, and is it supposed to loose vacuum as soon as the key is turned on? Any help would be greatly appriciated. The Pirtle and Nicholes sight were a real help getting me this far, but need a little more to finish the job.
Thanks again
JOHN
87S4

IcemanG17

John
The orange line (center comb flap) also leaked on my 88. From what I understand if it leaks even a little bit it will flap at odd intervals which is very annoying? Mine was like yours and didn't hold any vacuum at all. The WSM shows the function diagram for the control panel/actuators. One thing you could try is capping both leaking lines, then see if it fixes the problem. If it does then your only problem is the vacuum leak...fixing the actuators would solve the problem. If it doesn't...then it must be electrical...I don't know about the electrical side of the system? Also try looking at Wally's site on 928gt...good stuff there....also Tony's site too
Brian

docmirror

At least one of the vacuum solenoids is default open with key on. That is the heater valve. So, when you pull vac, then switch on the key, you apply vacuum to the heater circuit, and possibly the center comb flap circuit as well. I believe that's why the Orange center comb flap fails so often, that it is held in with vacuum any time the car is running. Only switched off during defrost? Can't recall fur certain.

If you hold a vacuum at the black line TO the manifold, then all the solenoids are sealing. Whether they open at the right time or not can be tested by applying 12V to each solenoid when you have the center console off to repair the orange vacuum diaphram. They are switched by the slider in the AC control head. You can test the slider positions with a ohm meter when the control head is out. A good WYAIT is to replace the AC pick relay with an external one. Mine failed only hours after doing all the fancy vacuum work, and I had to pull the control back out. Ugh.

Doc