2003 Toyota Highlander, A/C Stuck On Heat, Part 2

Well this 2003 Toyota Highlander with the a/c stuck on heat finally made it back in so that I could find out what is wrong inside the a/c control assembly. I am planning on fixing, hopefully some weak solder connections. The temperature control switch had been loose and I tightened that up and the system went back to work for about a day before it failed again. I have found that even though the switch is now tight in the assembly, if I rock the knob up or down slightly rather than rotate it the blend air door will shift back to cool. The simple diagnosis is, if there is no control over the temperature control, remove the knob (pulls off) and check to see if the retaining nut is loose. Tightening the nut should restore operation temporarily and confirm that there is a broken wire inside the assembly.

To remove the assembly I first started at the lower edge of the trim panel and started pulling it out from the dash and worked my way around to the top side of the panel.

With the trim panel removed there are six, 10 mm headed blots that have to be removed. Be careful not to drop any. I dropped one and it took me about half an hour to find it.

Next I tilted the assembly away from the dash and removed two screws from both sides. I then had to pry the bracket away from the control assembly in order to clear the alignment pins.

Of course I had to unplug the wiring but it was too tight to get a picture of this but you can see the three connectors that I had to remove. I did not disturb the radio wiring because of the possibility of loosing stored memory and anti theft issues.

With the control panel removed, I lifted the clear panel away so that I could unplug the ribbon wire cable.

There is a plastic retainer that looks like part of the socket. It needs to be gently lifted to release the locking mechanism. I used a pick with a 90 degree bend to lift each end about an 1/8″. If this clip is not properly released,  it will either break or shoot out and possibly be lost. Either way the job is over and you will have to buy another control head assembly, so be very careful.

Then the cable pulls straight out.

I then removed the screws that held on the rear cover.

Once the cover was removed I continued removing the screws that held the circuit boards in place and removed the nuts that held the switches in place.

With the circuit boards and switches removed from the assembly I could now see the real problem. Two of the three wires that connect to the switch circuit board were broken.

I clipped the last wire as close as I could to the circuit board. Once removed, I heated the broken ends of left over wire in the switch and pulled the pieces out with very small pliers. I then ran a piece of very small steel wire through the holes to clear the remaining solder. I used a razor blade to remove some insulation from the wire lead, fed the wires through the holes and soldered in place.

In hind sight I think on the next one that I will assemble the board and switches back into the control assembly and then solder the wires.

There was a little tension on the wire lead, that I did not care for, as I assembled the unit back together, so I heated up the leads a little and let the wires slide back far enough to take the tension off of the wires and the circuit boards.

I installed the control assembly back into the dash.

Then finished by testing and installing the trim panel.

The soldering and repair work internal to the control assembly was quite tedious and if you are not used to doing this kind of work, I would recommend taking it to some one that is. At least you will know what is wrong and you will not need to buy a control assembly that costs right at $700. For more information on the system please click here for part one.

I have added a few pictures and more detailed description in the above article. I am also updating the technique used to repair the solder joints.

There is not much excess ribbon cable and hardly any of us have that just laying around, so I use a razor blade to remove some of the insulation.

Exposing about 3/16″ of wire. I preclean the solder and old wire from the switches circuit board. Install the switch in the control assembly. I then guide the wires through the cleared holes on the exposed side of the switch circuit board. I gently mount the main circuit board back into the control assembly, pull the ribbon cable back slightly and solder the wires into place.

I find this much easier than trying to work the ribbon cable through from the original direction.