Climate Control Diagnostics:

5000 100 / 200 Type 44 & V8 D1?

Early GM type Climate Control (CC) Head diagnostics

Display dot flashing?  Click here:

The newer 1992 and up versions are supposedly able to do 68 or so channels.

This process is so simple yet can be frustrating if the exact sequence isn't followed.

Ignition ON:  With the unit off.  Press & hold Outside Temp FIRST.

HOLD(ing) outside temp down and simultaneously press OFF, release.

The hash mark denotes diagnostic channels.  Here is channel 01

On channel "01" pressing the Warmer / Cooler make up cycle thru the channels numbers. 

21 channels up to August 1988, 22 channels after August 1988.

Here I'm pressing WARMER to keep going channel "03"

The red light under the channel "03" is the digital camera.

Once you're on a channel you want, press "OUTSIDE TEMP" once for the reading / value.

"155" is some value on another channel.  The Bentley manual has a table for these values.

Below the HVAC control flap motor positions can be determined on certain channels.

Here is a value output display.

Channel "11" shows the battery voltage below of 12.0 volts.


Channel ## : "Value"

01 System error "00" = no error, "09" = coolant temp interruption

Values on Channel 01 range from "00" - "16" table values pg: D8 - 30 - 1.

02 Inside temp sensor in roof

03 Inside temp sensor in Instrument Cluster

04 Outside Temp G57 Plenum

05 Outside temp cowl

06 Coolant temp..phased in production 255 = open circuit.

07  Graphic display of output control for A/C programmer.

08  Potentiometer feedback value HVAC flap servo motor.

09 Specified/setting? potentiometer feedback value HVAC flap servo motor.

10 Specified voltage on fresh air blower  (see channel 15)

11 Vehicle Electrical voltage (12.0 volts or other)

12 Total number of elctrical voltage interruptions

13 Program number

14 Switch position of high pressure switch F118 (red housing)

15 Specified voltage on fresh air blower (in volts)

16 Pulse counter (useless) 0 - 256

17 Graphic display of compressor shut-off conditions

18 Graphic display of electrical conditions

19 Number of times compressor shut off via high pressure switch

20 same as 19 except time during ignition cycle / last drive only.

21 Program number, useless

22  Signal Speed from Aug 1988 on: 00 vehicle stopped, 01 moving.





Below if the red dot by the outside temperature is flashing:

Some major issue has happened or radical HVAC condition is vastly different than before.

Mine blinked after I bought the car since a deer strike impact for a day or two then stopped.

Page D8 - 10 - 2 in the Bentley lists:

A/C high pressure switch off  eight times during last drive.

Temp sensors inside / or outside sending incorrect values

Potentiometer regulating flaps have incorrect values for the CC settings.

Source(s):  Bentley Publishing service manuals.