1991 ranger ac

[cmepoo]

I cant seem to locate the problem with the ac contoller in my 1991 ranger 4.0l i have power comming to my ac contoller via yellow with red stripe. while holding a test light on this wire and turnning up the fan blower the light dims each speed more until on hi the the yellow with red stripe becomes and ground and will flash on test light. If i jump the purple wire in the ac contaller the ac compessor comes on and blows cold on all settings

 

[Mirage]

From what you described my first guess is a problem with the fan speed control itself. You said the voltage decreases (lights dim) on each consecutive speed setting until there is no voltage at all at full speed. Am I correct? Does the fan actually rotate faster at each speed setting? If not, then I would suspect the fam motor.

One easy check might be to disconnet the fan motor from the control and operate the control. If the lights continue to dim, then the control is deffinately the culprit.

Keep us posted.

 

[cmepoo]

Yes the fan works fine. when i jump the purple wire with a seperate hot wire clutch comes on and all wokrs perfect. thinking it might be the relay under the fuse box under the hood. but wont know until i change it

 

[srteach]

The fan speed resistor is operating correctly. You are looking at (and seeing on your machine) parallel current. Each setting has less resistance through the fan than the next slower speed, until there is no resistance at full speed. This is the way you get multiple speeds out of a 12V electric motor (which is what turns the squirrel cage blower).

Your AC compressor is not turning on. This could be caused by a bad relay, a low pressure situation in the system (lack of R-12 or R-134a), a bad pressure switch or a bad compressor clutch (not likely if it works when jumped).

Those are the things I can think of off the top of my head.
If you are jumping the purple wire and getting AC compression, I would think pressure switch or faulty in-cab switch. This is my GUESS.

 

[cmepoo]

thought it was the relay but not the case. What color wire id the main power source for the ac controler. seems like that might bethe issue. corrcect me if im wrong. power into ac controller---puts power to the purple wire in ac contoller---that wire put power to low pressure switch----which puts power to the relay to activate the points----witch send power to the ac cluctch. i can not get power to the purple wire in ac controller just replaced it with one from junk yard maybes its bad to. im thinking its the main power into ac controller?