Weird AC Behavior

Eric_R_Kissell at Eric_R_Kissell at
Fri Aug 16 08:53:23 EDT 2002

What if the vacuum check valve was leaking so that positive pressure could
leak past when you are on boost? This could cause a vacuum problem
periodically, depending on the rate of the leak and your driving habits for
that time period.

However, I looked in Bentley and it clearly shows:

On the Auto setting the dash vents are meant to be closed on the high fan
setting but full-open on the low fan setting.

On Bi-Level you can expect partially-open center vents for either fan speed

On Econ you should expect full-open center vents for the low fan setting
but closed center vents for the high setting, just like the Auto setting.

Defrost shuts the center vents, as you would expect.

I took a zip-tie and tied the center vents full-open continuously for now.

There is also a note which says:
"If a failure occurs in the vacuum system, the digital climate control
system switches automatically to DEFROST."

So, if the vacuum check valve leaked and allowed boost into the vacuum
tank, the system might default to defrost.

Also note that the heater valve is OPEN on all settings except OFF and Auto
with the low fan speed. I assume this is so the system can blend warm and
cold air to maintain the set temperature. Notice that this means the heater
valve is open for the high fan speed in Auto and both fan speed settings in
Econ, Bi-Level, and Defrost.

Note, the preceding comments were from the Bentley for the 1986-1988 5000.
I will have to check and see if the 1989-1991 200 Bentley shows anything


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