90q20v heater valve kablooey

kf21857 at comcast.net kf21857 at comcast.net
Mon Nov 20 15:13:17 EST 2006

Thanks, that explains why my @#$#$ air conditioner never has worked right.  It takes a loooong time to cool down once you switch it on.  I may be able to glue the old valve back together with PVC cement but where the vacuum hose went is still a mystery.  I thought it might originate at the controller but I thought I should check before I started tearing the dash apart.  Thanks for your help.

-------------- Original message -------------- 
From: Kneale Brownson <kneale at coslink.net> 

> The vacuum hose should come from the climate control controller. It should 
> shut off the heater valve while the A/C is in operation. Probably lowers 
> the ambient air temp in the heater core box, where the air passes through 
> without going directly over the heater core when heat isn't called for, 
> from ~200 degrees F to whatever the outside air temp is. 
> The version of that valve with the sensor is NLA. You can replace the 
> valve with a metal version from FLAPS for around $20. The plastic valve 
> without the sensor is available from most import parts sources for a 
> similar price. 
> At 04:44 PM 11/20/2006 +0000, kf21857 at comcast.net wrote: 
> >Hi, I am a former list member but haven't been subscribed in a while because 
> >my car hasn't broken in a long time. 
> > 
> >My 90q20v with climate control has a vacuum actuated valve with a water temp 
> >sensor in the heater hose a few inches from where it enters the firewall. 
> >Yesterday the two halves of the valve separated while I was stopped in 
> >traffic, causing the cooling system to empty itself rather quickly. 
> >Fortunately I was able to find a parking spot, remove the two pieces from 
> >the heater hose, unload the mountain bike I had on the roof and cycle to a 
> >hardware store to find a suitable part to splice the hoses back together. 
> > 
> >Here are my questions. I am planning a parts run to the local Audi dealer 
> >to order a replacement today, but I have spent quite a bit of time searching 
> >for the vacuum hose that is supposed to control this valve and it simply 
> >isn't anywhere to be found. I had noticed the valve before and wondered why 
> >there was no hose going to it but had concluded that there just wasn't 
> >supposed to be one. The valve defaults to open position when there is no 
> >vacuum applied so the heater works OK. Exactly what is the function of this 
> >valve and when is it supposed to be closed? Could this be the reason why my 
> >A/C has never worked worth a darn? And where is the hose supposed to 
> >originate? The Bentley shows a schematic with all of the vacuum operated 
> >controls on the heater but I haven't found anything telling me where to find 
> >it. I am guessing that it is under the dash somewhere. Do I really need to 
> >replace this thing? Is it vitally important? It looks rather expensive and 
> >I have made a semi p 
> >ermanent repair by clamping a pipe nipple in place of the valve. 
> >thanks, 
> >Dave 
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