1990 Buick Electra

Air Conditioning problem
1990 Buick Electra 6 cyl Front Wheel Drive Automatic 275000 miles

How do I decide what the problem is with this automatic HVAC system? Got the car 3 days ago - was told the AC blew erratically, blowing out the defrost if fan speed on HI or not at all. Controls are electronic, automatic with only 3 fan speed options: LO, AUTO, HI. The blower worked fine when I connected the terminals directly to battery. There is a creaking noise each time the system is turned on initially but no air flow. None of the fan speed controls affect anything. No blower noise at all. None of the control panel buttons do anything. Compressor works, condensor is cold and sweating. At highway speeds, seems like some minimal cold air comes out of the dash vents. How do I know if its the Blower Control Module or the the control panel itself that is the culprit? Or could it be something else simpler? No fuses blown but don't know how to check relays or resistors. The + lead to blower motor is hot when disconnected from motor; dead when connected, with & without AC turned on. Is that the way its supposed to work?
Please help.
September 20, 2010.

The A/C control panel uses switches for selecting operating modes, in-vehicle temperature, blower motor speeds, and outside air temperature. Temperatures may be displayed in either Fahrenheit ( °F) or Celsius ( °C).
The assembly contains a microprocessor which receives signal input from panel switches, temperature sensors, and the air mix door feedback potentiometer in the programmer. Blower motor speed is also monitored. The control panel uses this input to position the air doors and control the blower motor speed. The microprocessor will retain all selected settings when the ignition is turned off.
The control panel microprocessor is also capable of self-diagnosis for some system circuits and sensors. If a fault is present, a trouble code will be set in memory. Diagnostic trouble codes can be displayed on the control panel.

If "EXT TEMP" indicator is flashing during first few seconds after engine is started, this indicates a trouble code set in memory. To enter self-diagnostics, turn ignition on with engine off.
Press hidden diagnostic button between "EXT TEMP" and "HI" buttons. To exit diagnostic mode, press "EXT TEMP", "WARM" and "COOL" buttons at same time or cycle ignition switch.

check control module and it plug

Sep 20, 2010.
So are you saying the module needs to be replaced? Where do I find help interpreting the code readout from the HVAC digital display. It read 00 when I pressed the hidden button.

Sep 20, 2010.
00 no codes
check the module before

Sep 20, 2010.
Thanks for the help. I changed the module and now have air but it still blowing out of wrong vents. Comes out Defrost when on Auto. Which part do I check or replace now? I appreciate your expert help.

Sep 21, 2010.
Check vacuum supply lineto the programmer.
The programmer converts electrical signals from the A/C-heater control panel into vacuum commands to air intake and distribution doors.
The programmer is mounted under the right side of the dash, attached to the heater core/evaporator housing.
Vacuum source is from a vacuum reservoir tank, mounted next to the power brake booster.
Vacuum is constantly applied to the programmer check valve which distributes the vacuum to 4 solenoid-controlled valves. When the control panel signals the programmer to change an air distributor door position, a solenoid is energized and vacuum is applied to a vacuum actuator. The actuator will then reposition the door. The doors controlled by the programmer are: outside air-recirculation, defrost-A/C, and the mode door (bi-level, heat and A/C positions).

Sep 22, 2010.