I figured I would try over here since the AC codes are the same.... Yesterday the air conditioner was working today kaput. I ran the diagnostics on it, and I got code 24. I reset the code drove the car came back to code 24. I had an extra "wheel" for the front vent and tried that...nothing. Any help would be appreciated.It almost feels like it is blowing hot and cold air, and I see the compressor's clutch turning. The error states - Face vent demand potentiometer fault Potentiometer open / short circuit Harness/connector fault Refer to PDU. Will the PDU actually tell me what the problem is?

 

The wheel pot is feed 5 volts DC as a reference voltage and the returning voltage is what the climate control ECU works with to move the servo to its position

So a simple resistance test of the potential pots as a stand alone item for both your pots will let you know if both of them are good

The wheel potentiometer is not present on the later V8 X308 model using the same Denso climate control system , must have been too many problems right off the production line

The louver vanes can break if removing the vent box from the center of the louvers

The servo has a position sensor in it to see it has an agreement that the servo has moved to its commanded position so the servo motor can be good and serviceable but a bad position sensor

You can drive the servos to the desired position ( and this test the motors ) with a 9 volt battery and you flip the polarity to drive the motors back and forth if you listen real hard

To drive the servos you would be at the ECU connectors and not the center vent potentiometer connector

 

I tried to use a known good "dial," and it reacted the same way. I pulled out the vent, disconnected the "dial," used another dial, and did the same thing. I wonder if there is a way to remove it from the system to ensure it was not the problem. I don't feel like tearing the dash apart to get to the ECU. I would assume I could pull out the connector and use the battery on the female connector. Luckily on the X100, you can reach the female end from the center vent. There is a connector that you can pull up long enough to reach it from the center vent.

Well, I took it out again this morning and tried to run the AC. It never got cold, and Error code 24 never returned, so I will drop it off today to check the refrigerant. After all, it is a 26-year-old car with 20,000 miles. It worked when I got it, but maybe I used it all up or had a leak.

 

By removing the connector at the vent wheel pot the ECU sees 0 volts as the return signal and would swing the door in one direction

Jumper Ing the reference voltage to the return wire will swing the door in the other direction

This test would point the finger at the pot being bad

So in theory removing the connector goes hot position and jumper Ing goes cold for your season in New Mexico

The caution is taking the purple wire to ground as it might blow the 5.0 volt reference signal generator in the ECU

 

So you are saying if I jumper the OU---->BW should open it for the AC? Removing it after I jumper it or add a 9vt source, I should be OK. In the winter time I will just have to connect it again. I will go this morning and get the system charged and see if that fixes it first.

 

Removing the connector will close the servo door or hot

Purple to Orange / Blue will open the servo door or cold

Never Purple to Black / White

The green line in the plenum pic is the upper and lower half's as they are made and with the center vent louver box removed you might see the servo door move and hear

If not you can take a piece of spaghetti as a feeler and if the spaghetti gets in the way it will just break off

Or you can use bread bag twisties found in the produce isle

Using a 9 volt battery is not needed at the vent wheel pot connector. unless the 5.0 volt signal generator in the ECU is not working

In that case I would use 3 battery cells or 4.5 volts on the Orange / Blue wire