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TOPIC: 1990 HVAC

1990 HVAC 21 May 2020 21:14 #21224


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i have a 1990 s4 127K miles i have a HVAC problem for no reason the solenoids will start open and closing real fast and can't get them to stop has anyone had anything like this happen before ? if anyone can help my email is This email address is being protected from spambots. You need JavaScript enabled to view it. my cell 818 599 9948 thanks
Last Edit: 21 May 2020 21:17 by jk1990s4.
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1990 HVAC 29 May 2020 16:26 #21238


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What solenoids are you referring to? What is the general location of the components/solenoids, and what is it they're doing that makes you say they're opening and closing? Are they making sounds of some sort?
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1990 HVAC 29 May 2020 17:36 #21239


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Hi they are the solidionds that activate the pods to open and close different vents be it the air flow going to the center vents or to the floor or defrost ect they have all the different vacuum hoses coming in so its in the lower center of the dash if you open the driver side panel you would see the vacuum line thats there it is and as I'm driving for no reason they would get activated and fire off real fast thus opening the pods i had the pull the brown ground wire that dos to that unit to make them stop and if I'm driving and i hit the brakes that makes them go off too . have you and idea what it could be?
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1990 HVAC 29 May 2020 20:37 #21240


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The most common cause of what you're describing is that the rubber diaphragms in the control actuators for the various doors in the HVAC ductwork have developed holes and are losing vacuum. Check out to following link which explains what's happening and how it can be addressed, and give Jeannie a call at www.928gt.com for the parts you'll need.
dwaynesgarage.norcal928.org/1987%20HVAC%...pair%20Procedure.htm
Last Edit: 29 May 2020 20:40 by y33trekker.
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1990 HVAC 30 May 2020 10:43 #21241


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ok ill check that out thank you very much
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