1972 deville ac wire diagram

[72daddy]

i have been having problems with my ac it only blows on high and defrost when in low it turns on the compressor but not the the blower motor i replaced the ac switch and blower motor and even the resistor with blower relay and still the same thing I'm lost

["Cadillac Kid" Greg Surfas 15364]

If the fan does not operate in "Auto" I would suggest either the "low" relay or the connection at that relay might be defective.
Greg Surfas

[TJ Hopland]

What sort of ambient conditions?    I don't have time to look at a manual but there are several ways the blower can run depending on ambient temps, engine temps, and selector switch position.     

If you are having this issue now and ambient temps are on the cooler side where you are I would suspect the sensor in the corner of the head behind the alternator.    If the cabin temp is below something like 75*F you won't get full blower speed in auto till it thinks the engine has warmed up to 120*.   At 120 that sensor behind the alternator grounds and lets the blower run at what ever speed the system thinks is needed.    If its over 75 it will let the blower run before the engine is warm because it figures you will want AC. 

I may be a little off on the details but that is the basic concept of the system.  Some of the details were slightly different year to year so you want to be looking at the manual for your year.     Its not that complex of a circuit so its pretty easy to follow on the diagram and see what modes require what sensors and what temps those  sensors operate at.   

[Scot Minesinger]

Please consider purchasing Cadillac Tim's 1972 Cadillac climate control manual (google Cadillac Tim, Iva, SC).  He sells many rebuilt parts too.  This could be a multitude of issues and difficult to diagnose over the internet.

The connections, the programmer and the dash switch are the weak links in my experience.