1986 420 SEL: Automatic Climate Control W126

[Buick8]

Compressor and refrigerant-containing parts are good; blower comes on and will run about 20 seconds at High speed, then stops abruptly and will not come back on. If the ACC is turned off, then back on, it will repeat the 20 second routine.
Additionally, I note the system seems to only operate with automatic blower speed; it will not respond to either the High or Low blower-speed selector buttons (this symptom was present prior to the development of this problem, however). Hot air seeps from the windscreen demister vents and the right and left panel vents when the system is off, making it somewhat uncomfortable (and increasingly so, as Spring has arrived).
Any troubleshooting help and description of your experiences would be most helpful.
Regards, from Randy

 

[Francois]

The hot air problem ussually stems from the duo valve between the two fire walls acting up. Best course is to replace it.

This valve regulates the hotware supply to the heater. If the solenoids stop working, it is in the always on position.

 

[Buick8]

420 SEL auto climate control

Thanks, that is a great suggestion. meanwhile, I am about to venture into the blower control as the blower has completely stopped. Probably one of the resistors, or else the pushbutton control (the blower would only work in auto before this latest failure, anyway; HI or LOW had no effect on blower speed).
regards