Heater Hot, then Cold

Phil and Judy Rose pjrose at frontiernet.net
Sat Jan 3 16:29:51 EST 2004

At 10:13 AM -0800 1/3/04, George Sidman wrote:
>I went through this one last year. It was the vacuum control box
>under the dash (behind glove box) went bad. If you pull it and
>pop it open you will see the five foam pads that seat the vacuum
>valves are burned from failed board electronics. I found a used
>one by chance on this list, otherwise replacement from the dealer
>was the only other alternative.
>You can check the motor and control valve on the heater box by
>going through the test suite from Bentley.

If you don't have a Bentley manual available, the climate control 
diagnostic channels 08 and 09 show, respectively, (a) the desired 
position for the flap-potentiometer (to satisfy the combined "set" 
and outside-air temperatures) and (b) the actual potentiometer 
position reached. So, when your heater starts blowing cold when it 
should be warm, check to see if the CC channel 08 and 09 values are 
in fairly close (not necessarily exact) agreement. If the two 
readings are are similar, then problem is elsewhere. Also, the actual 
flap potentiometer reading should be steady or very slowly changing 
(not display large, rapid changes in value). My guess is that the 
problem _is_ the potentiometer.

*  Phil & Judy Rose           Rochester, NY  *
*        mailto:pjrose at frontiernet.net       * 

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