How do I test HVAC Vacuum Servo Solenoid Valves
10-25-2003, 11:00 PM
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How do I test HVAC Vacuum Servo Solenoid Valves
I am in the midst of fixing vacuum leaks on my 88 S-4. All servos are leaking except for the hot water valve. No wonder I have hvac problems. My problem is that I don’t know how the vacuum servo solenoids are supposed to work. I have all the lines to the solenoids plugged and I am using a MityVac to apply vacuum. With the ignition on I can hold vacuum only in the defrost setting. If I move the lever to any of the other settings I lose vacuum and I have a vacuum leak. I disconnected the power wires from all of the solenoids and tested each one individually and found that when I applied power one released a small amount of vacuum then held. All the other solenoids lost vacuum, some faster than others and continued to leak until I shut off the power to that particular solenoid. Can anyone tell me how they work?
10-26-2003, 12:05 PM
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I believe I have the answer. After I posted my question I rummaged around through some old parts and found some working solenoids. When power is applied to the solenoid it should hold vacuum and not leak at all. Once power is turned off the solenoid does not allow any more vacuum to enter it. The confusing thing for me was how the actuator returned after the vacuum was shut off. Once power is turned off to the solenoid it opens a port to allow air to enter the vacuum actuator so it can release.
10-26-2003, 04:13 PM
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Daryl,
If you don't have a copy of WallyP's 928 HVAC paper...I highly recommend you locate it. Sounds like you've got the Gestalt now, however.
I wonder if this is what is causing my A/C to deliver cool (not cold) air in the front vent (main) and ice cold air in the rear A/C of my 89 s4? System has been converted to 134a but has the original compressor and all else. I know that the PO (Gary T) had all of the vacuum lines and various related bits replaced when he had the engine out for resealing not too long ago. Your thoughts appreciated...
If you don't have a copy of WallyP's 928 HVAC paper...I highly recommend you locate it. Sounds like you've got the Gestalt now, however.
I wonder if this is what is causing my A/C to deliver cool (not cold) air in the front vent (main) and ice cold air in the rear A/C of my 89 s4? System has been converted to 134a but has the original compressor and all else. I know that the PO (Gary T) had all of the vacuum lines and various related bits replaced when he had the engine out for resealing not too long ago. Your thoughts appreciated...
10-27-2003, 12:57 AM
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Hello Tuk_928
Thank you for the advice re Wally P's paper. I do have it. Thanks to that paper I was able to understand and work out all of my air conditioning problems with my 80 928. Wally has a great gift of explaining how things work so people with limited knowledge can understand them. Please write a book Wally!
Based on the fact that the rear air is ice cold and the front not my first guess is that you do have some vacuum problems or problems with vacuum actuated devices. Do you have a MityVac or some device to check vacuum integrity? If yes I can explain the steps I took to find and eliminate all of my vacuum leaks with the HVAV system as well all other vacuum related systems in the car. Let me know if this would be helpful to you.
Thank you for the advice re Wally P's paper. I do have it. Thanks to that paper I was able to understand and work out all of my air conditioning problems with my 80 928. Wally has a great gift of explaining how things work so people with limited knowledge can understand them. Please write a book Wally!
Based on the fact that the rear air is ice cold and the front not my first guess is that you do have some vacuum problems or problems with vacuum actuated devices. Do you have a MityVac or some device to check vacuum integrity? If yes I can explain the steps I took to find and eliminate all of my vacuum leaks with the HVAV system as well all other vacuum related systems in the car. Let me know if this would be helpful to you.
10-27-2003, 01:08 AM
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Daryl,
I agree...Wally should write a book. I really enjoyed reading the 928 HVAC paper he shared with me. I do not own any devices for checking vacuum integrity but perhaps this will give me the impetus to buy a MityVac. I would be very interested in your assistance. Thank you for your offer...this is why I joined the Rennlist! Thanks Daryl!
Best,
Tim
I agree...Wally should write a book. I really enjoyed reading the 928 HVAC paper he shared with me. I do not own any devices for checking vacuum integrity but perhaps this will give me the impetus to buy a MityVac. I would be very interested in your assistance. Thank you for your offer...this is why I joined the Rennlist! Thanks Daryl!
Best,
Tim
10-27-2003, 01:01 PM
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Hi Tim,
I joined the Rennlist for the same reasons. I am a hobby car guy interested in learning how, and then repairing and improving my cars. I am not a Mechanic and totally self taught. So please keep that in mind.
I have found the support from our fellow Rennlist members, others who have made their own web sites and suppliers invaluable. I thank them all! I could not be in this hobby without them. Do you know how to use the search function on Rennlist? I got most of the information I have from searching the archives and checking out web sites. As well the manuals and parts books are available on CD. Let me know if you need more info regarding these things. I found another great article by Wally P regarding tracing vacuum leaks as well as Dr Bob and many others. Let me know if you need further info on these things as well.
With both of my 928’s I have had major vacuum leaks. If you are serious about vacuum leaks you must get a MityVac. You need this tool to find the slow leaks. A small investment compared to the returns in enjoyment of your car. Let me know when you are ready and I will walk you through what I did to find the leaks on my car. You can also email me at daryllmiller@hotmail.com if you like.
Best regards, Daryl
I joined the Rennlist for the same reasons. I am a hobby car guy interested in learning how, and then repairing and improving my cars. I am not a Mechanic and totally self taught. So please keep that in mind.
I have found the support from our fellow Rennlist members, others who have made their own web sites and suppliers invaluable. I thank them all! I could not be in this hobby without them. Do you know how to use the search function on Rennlist? I got most of the information I have from searching the archives and checking out web sites. As well the manuals and parts books are available on CD. Let me know if you need more info regarding these things. I found another great article by Wally P regarding tracing vacuum leaks as well as Dr Bob and many others. Let me know if you need further info on these things as well.
With both of my 928’s I have had major vacuum leaks. If you are serious about vacuum leaks you must get a MityVac. You need this tool to find the slow leaks. A small investment compared to the returns in enjoyment of your car. Let me know when you are ready and I will walk you through what I did to find the leaks on my car. You can also email me at daryllmiller@hotmail.com if you like.
Best regards, Daryl
