Re: HVAC saga continues, '875kcstq

[Wallace White <wallace@remdesign.com>]

Hi Nick,

> A week or so ago I inquired of the list regarding the little DC motor on
> the AC programmer that drives the cable that regulates the temperature
> flaps.......Well, I ended up getting a rebuilt programmer plus motor
> through Mountain Automotive in Colorado (good folks to deal with so
> far).  The new programmer seems to do its thing just fine, but only
> after I've  driven the car for about 20 miles/minutes.  When I start the
> car cold in the morning, the system maintains whatever temperature
> setting (IE, cable/flap position) it was in when I shut it off the night
> before, regardless what temperature I punch in on the dash (does go into
> defrost mode when I punch defrost, but temperature is still not
> regulated).   After about 20 miles, I can hear the little motor begin to
> hum; the flaps move, and the temperature begins to be regulated.  At
> that point I can dial the temperature setting up or down, and the system
> responds as it should for the rest of the trip.  

I've never watched the motor during the warm-up period, but I do know
that the system isn't supposed to start blowing heat until the engine
passes a certain temperature. But it shouldn't take 20 miles, unless
it's _really_ cold, for the engine to get that warm. At 28 degrees this
morning (cold for the San Francisco area!), my heat came on within two
or three minutes, I'd say.

> Additional data:  the
> little sucking motor in the center of the dash is working; I have not
> gone in there to check the connection/functionality at that temperature
> sensor (doesn't seem  like I can get there from here without major
> dismemberment of the dashboard....); I've cleaned the connectors at the
> back of the AC controller head on the dash and at the programmer behind
> the glove box; the 2  outside temp sensors are in place and connections
> seem OK.

Ah, have you used the diagnostic mode of the AC head yet? It can answer
all of these questions. The Bentley gives full detail on it. By holding
OUTSIDE TEMP and pressing OFF, you invoke the diagnostic readouts.
Readouts are given on 23 channels; the first one you'll see is '01 (the
apostrophe is the head's way of telling you that it's a fault channel
number). 01 is the error reporting channel. To read the value of a
channel, press TEMP COOLER. To change the channel, press TEMP WARMER
till you hit the right channel number.

In the '01 example, you should then see 00 for no faults, or 07 for the
temp flap motor not being able to hit its target. Any time that the
Outside Temp light flashes, there is an error that can be read on
channel '01. (By the time you get there, though, it may say 00 if the
error is no longer present.)

Other interesting channels include '03, '04, '05 which are the
temperature sensors A/D values (I forget the order). With those and the
lookup table in the Bentley, which tells you what temperature the
displayed value corresponds to, you can tell if your temperature sensors
are working properly. Also of note are '07, which is the graphic display
of what the head is doing with the flaps and motor, '10 and '11 which
are the battery voltage and ventilation fan voltage (again, I forget
which is which). And there are many more. Anyone working on this (and
all the other stuff the car demands you work on) should _definitely_
have a Bentley to take full advantage of these features.

HTH!

- Wallace
  '87 5kcstq 151k