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After much work replacing the thermostat and it's housing to get heat back into my truck... and water going to the radiator... turns out that was not the issue after all.
Garage called me to say there still is no heat because the AC is running all the time. They are at a loss. They have checked all the vacuum lines to and from the heating controls and all appears to be fine. I'll be getting the truck back tomorrow and now I will need to find the issue on my own.
There is a video online that talks about something called the blend door actuator. A small white device that sits behind the glove compartment with a tiny motor and some plastic gearing that can get gunked up and stop working correctly. I'll pull this unit and take a look at it on my bench.
From what I've found... if this device fails it will lock the car in either heat or cold all the time so appears this may be the culprit. New one by Dorman is around $50.
Last edited by scooterspal; Jun 11, 2026 at 07:05 PM.
With the control in the OFF position, does the AC run? Does it run in FLOOR or VENT? Those are the only three positions that the AC should not run. In all other positions it is supposed to run.
It is not controlled by vacuum, so I don't understand why they checked the vacuum system. It is all electronically controlled.
With the control in the OFF position, does the AC run? Does it run in FLOOR or VENT? Those are the only three positions that the AC should not run. In all other positions it is supposed to run.
It is not controlled by vacuum, so I don't understand why they checked the vacuum system. It is all electronically controlled.
See these pics. I'm getting AC (compressor running) with these settings where I should not. I do get proper AC when set to AC.
When turning the hot/cold **** back and forth I do hear the door actuator click once, as it should.
Is there a separate set of electronics for HVAC or is this all off the master computer?
In the top picture, the AC compressor should not be on. In the bottom picture, the AC compressor will be running. It should not run in the VENT, OFF, and FLOOR ONLY positions. Whether the temp is set to hot or cold does not matter, it doesn't affect the compressor.
It is run from the control shown in the photos. No computer.
You should focus on the power wire to the AC compressor clutch. Make sure it doesn't have a short to power. And/or the AC compressor clutch itself. Maybe it's stuck. When they say "AC is on" they probably mean that the compressor is spinning.
If the compressor is spinning, fluid and gases will flow and cooling will occur.
OK, so I was incorrect. The AC compressor is running when the switch is set to the right (upper and lower) position but not when set to the left (vent) position. It was just that the cooler air was still felt when set to vent until it bled off. So, no the compressor is not running when set to vent.
I still do not understand why the AC compressor runs when set to the right (upper and lower) position. You say this is normal but I don't understand why this is so.
That said, I have found the issue with the missing cabin heat. The tiny vacuum line that controls the cabin heat exchanger is severed. The plastic hose material just worn out from 22 years of use.
I tied off the valve in the on position and the cabin heat started to come back.
I now have a another issue. There is a loud clicking sound coming from somewhere. See my new post in this issue, please
Last edited by scooterspal; Yesterday at 07:09 PM.
I still do not understand why the AC compressor runs when set to the right (upper and lower) position. You say this is normal but I don't understand why this is so.
It is to dehumidify the air in the truck. This keeps the windows from fogging.
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