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Discussion Starter #1
Hi All

I've got a problem with the heating/cooling system in my '04 Highlander CVX that I'm struggling to diagnose. It comes with the 2 dial/5 button climate control layout. Basically the heating and cooling functions work fine, the issue comes when trying to adjust the temperature. If I've got it set on 18c (sorry, Australian car) then the AC is icy cold - if you try to change the temp up to 18.5c or above then it starts blowing full heat. When adjusting the temp from 18-18.5c or above, it switches from the face vents to the floor heating vents on its own.

So far I've swapped the climate panel in the centre with one from the wreckers - same result. I've also pulled apart the panel and verified that the two dial switches are working with good contact. Most of the youtube instructional videos seem to be one of the ribbon cable wires coming off the switch and just needing a resolder.

I've also pulled apart the passenger side to get a look at the servos. I can verify that the re-circulation and vent control (even tho I can't see this one) servos work fine. The temperature servo when adjusted from 18 -18.5 runs the full length of its control adjustment (full cold to full hot) with no stopping in between. Any ideas where I should go from here? Is there a self check that I can run? Is there a cabin temperature sensor that could be malfunctioning?

I've got a diagnostic tool and multi meter but no repair manual so I'm at a bit of a loss where to start. The scan tool doesn't show any errors through the OBD port.

Thanks
 

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If you pull off the temperature knob and try rotating the shaft back and forth, do the wires connecting it to the circuit board swing back and forth with the shaft? If so, you likely have the ribbon cable problem. When those wires are able to move back and forth (due to the shaft not being fully tightened down), they break their connection over time and result in the intermittent behavior you are experiencing. I have a base model so my knobs are slightly different, but I have personally encountered that problem and had to resolder the wires. No problems after that!

If your the temperature control knob shaft is secure with no wire movement, though, you likely have a different problem.
 

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Update: So after a little digging, I saw a instructional youtube clip of a guy putting a '04 Camry into HVAC diagnostic mode by holding down 'auto' and 're circulation' at the same time while the ignition was off and turning it to on. The test returned an 11 (in car temp sensor) + 21 (ac solar sensor). As it was night, I was sure that was why I was getting a 21 back. This morning I took it outside and retested - Only returned a 11.

The hayne's repair manual doesn't contain any troubleshooting or information for the sensors. I found what looked to be a sensor mounted in the trim piece below the steering column. Was caked with dust that I cleaned out with compressed air and also looked to have a loose wire into the car side of the harness plug. All was well once I fixed those two issues. Car adjusts temperature normally in stages instead of straight hot to cold now.
 
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