This 2003 Toyota Highlander came in with the complaint that the a/c only puts out hot air. I confirmed the complaint and removed the glove box to access the air mix actuator assembly.
I had to push the hinge pins out to remove the glove box.
I then had to remove the screw and bracket that hold the cable.
With the glove box out of the way, I had to remove one screw and release some retaining clips in order to remove the white duct assembly.
I checked the feed back sensor (orange wire) and it was reading about .8 volts at the full heat position. I started moving the temperature knob while watching the voltage and I noticed that the actuator arm would occasionally move and the sensor value would change. I found a sweet spot and the actuator would move to almost full cold. Looks like I need to go to the control assembly.
I first wanted to check the switch and knob to make sure nothing was stripped and after pulling the knob off I found that the switch was loose in the control assembly. I tightened the nut and the system now works properly.
I would assume that the actual switch mount is one of the control circuits and it could not make proper contact with the nut loose. Well, this turns out to only be a diagnostic aid. I will have to go deeper into the control head as soon as the customer can leave the vehicle again. I checked on the price of a new a/c control assembly. Almost $700 from the dealer and the only service part is the blower switch. This one is okay.
I have fixed this one and I will be giving an updated post in a few days. Pretty delicate work but it saved a $700 control assembly. Click here for updated repair.
Hey Sparky, we have the parts ready to put back together but we cannot figure out how to connect the ribbon that connects the top circuit to the bottom circuit. Please help we are almost there.
Tightening the nut is only a method of diagnosing the problem and making a temporary repair. There is a link at the end of the post on how to repair the internal damage caused by the loose nut.
I had this same problem the first time and the knob nut was tighten. Now I am having the same issue again 1 year later but this time it is not the knob. Help PLEASE….
Chances are that something went a little wrong in the repair process. It is quite tedious. With a voltmeter check the voltage across the yellow and yellow/green wires at the actuator. Terminals 4 & 5 respectively or at the control assembly. Terminals 13 & 14. There should be a change in voltage as the temperature knob is rotated. Very confined work area. Be careful to not short anything while testing. Another thing of note is that as the actuator moves there will be a change in voltage on the orange wire. This is a feedback signal that tells the a/c controller what position the actuator is at.
Hey sparky just reinstalled the unit and still no heat. The guy who re soldered the wires checked continuity and everything was fine. Any Ideas why it is not working. Car was warm when I reinstalled it. I tried A/C too It was blowing cold but when I turned the knob to warm compressor did not turn off. Maybe potentiometer is bad any Ideas??? Let me know