Help diagnosing "correct" behavior of AC vacuum solenoids
02-19-2017, 02:09 AM
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Help diagnosing "correct" behavior of AC vacuum solenoids
Hi all,
I just finished diagnosing a "hot air" condition in the HVAC system of my 1981, US-Spec 5spd 4.5L. The diagnosis is covered in a separate thread here, but in a nutshell, it was a defective "setting motor".
Now that I've got good hot/cold mixture back, I noticed that my center vent flap wasn't opening, except when I turned my system "Off". I have the automatic climate system, lower slider is: OFF, ECO, AUTO, BI and Defrost.
I'm trying to figure out the "correct" behavior of the six vacuum solenoids in the HVAC system.
What I did was disconnect the manifold vacuum source (the source vacuum, not the actuator side).
I then turned the key to ignition so there was power, then connected a Mityvac to the source of each solenoid (one at a time), and pumped up the vacuum. I left the actuator nipple unplugged. Each solenoid would hold vacuum, ie, it acted like it was closed. For ECO, AUTO, BI and Defrost, the vacuum held (again, indicating the solenoid was closed). Only when I set the slider to OFF, did the solenoid "open" and allow loss of vacuum (via the unplugged actuator nipple).
With one exception...
The defrost solenoid never "opened", and would hold vacuum regardless of where the slider was.
I also noticed that each solenoid may not be the same. Two had a "4" stamped on top, three had a "1" and the defroster had a "2".
Now, I didn't run the engine to hot, or even warm. Ambient temperature was about 60F, and the car wasn't idling long... I read in the owners manual the following: "... At engine coolant temperatures below 113 F/45C, the air flow is automatically directed toward the windshield. At engine coolant temperatures above 113* F/45* C. the automatic climate control system resumes normal operation."
I can confirm that air was going to the defrost no matter what setting I had the slider at.
So... does anyone know: 1) If there are different solenoids (ie, they're not all the same), 2) if the behavior of my defrost solenoid is normal and 3) Just what is the expected behavior of these solenoids?
Any other input would be helpful as well.
Thanks all!
I just finished diagnosing a "hot air" condition in the HVAC system of my 1981, US-Spec 5spd 4.5L. The diagnosis is covered in a separate thread here, but in a nutshell, it was a defective "setting motor".
Now that I've got good hot/cold mixture back, I noticed that my center vent flap wasn't opening, except when I turned my system "Off". I have the automatic climate system, lower slider is: OFF, ECO, AUTO, BI and Defrost.
I'm trying to figure out the "correct" behavior of the six vacuum solenoids in the HVAC system.
What I did was disconnect the manifold vacuum source (the source vacuum, not the actuator side).
I then turned the key to ignition so there was power, then connected a Mityvac to the source of each solenoid (one at a time), and pumped up the vacuum. I left the actuator nipple unplugged. Each solenoid would hold vacuum, ie, it acted like it was closed. For ECO, AUTO, BI and Defrost, the vacuum held (again, indicating the solenoid was closed). Only when I set the slider to OFF, did the solenoid "open" and allow loss of vacuum (via the unplugged actuator nipple).
With one exception...
The defrost solenoid never "opened", and would hold vacuum regardless of where the slider was.
I also noticed that each solenoid may not be the same. Two had a "4" stamped on top, three had a "1" and the defroster had a "2".
Now, I didn't run the engine to hot, or even warm. Ambient temperature was about 60F, and the car wasn't idling long... I read in the owners manual the following: "... At engine coolant temperatures below 113 F/45C, the air flow is automatically directed toward the windshield. At engine coolant temperatures above 113* F/45* C. the automatic climate control system resumes normal operation."
I can confirm that air was going to the defrost no matter what setting I had the slider at.
So... does anyone know: 1) If there are different solenoids (ie, they're not all the same), 2) if the behavior of my defrost solenoid is normal and 3) Just what is the expected behavior of these solenoids?
Any other input would be helpful as well.
Thanks all!
