The temperature control on my 2001 ETC continues to intermitently zoom up to 90 degrees from whatever setting I've chosen. I'll turn the adjustment knob back to my normal 72 degrees, then it does it again, and again, etc.

My first question: Is the automatic a/c and heat temperature operation controled, at least in part, by the mid-dash sensor ball?

And, if so, could car wash establishments have put dash treatment/cleaner on the sensor, to the extent that it leaves a film which interfers with the proper sensing operation?

In other words, could this be causing the zooming temperature problem described above?

And, if so, what can I use to clean the sensor without damaging it?

Sure would appreciate any help on this.

Best regards, Jack M.

The "ball" sensor you are talking about is the sun load sensor. I believe it comes into play when in the A/C mode. I am not sure but I don't think that is your problem. Just off the top of my head I would think maybe the in-car tempurature sensor. At least I'd start there.

The "ball" sensor you are talking about is the sun load sensor. I believe it comes into play when in the A/C mode. I am not sure but I don't think that is your problem. Just off the top of my head I would think maybe the in-car tempurature sensor. At least I'd start there.

Ranger is right. The temperature "setting" should not change unless it is changed by the HMI (human machine interface) If the interior temperature displays 90F when you know it is not, or if the outside temperature displays 90F when you know it is not, then it is a sensor problem. If the actual comfort "setting" changes, that suggests a short which needs to be addessed as soon as possible. The problem may be as simple as a bad connection, but if allowed to continue could damage the HVAC module.

Thanks guys for the quick responses suggesting sensor or shorting problems.

To make the actual symptoms a little more clear: When the digital temperature display zooms uncommanded from 72 degrees to 90 degrees, it's accompanied with a blast of hot air from the vents. It's not just the display problem -- it's also the climate control change inside the car, all without me touching the setting knob.

Yesterday, it was 82 degrees outside temperature in the Houston area, and I had the temperature set on 72 degrees while driving to the golf course. In the nine miles it took to get there, the zooming occured 5 times. Each time I reset the knob to display 72 degrees, it zoomed back up to 90 degrees with the blast of hot air -- all uncommanded. A few times, it didn't wait for me when I dialed it down -- it would zoom back up to 90 when my first twist of the wrist got the knob display setting down to 79 or 80 degrees.

The only difference I noted driving back home was that the zoom would stop on 85 or 86 degrees, with slightly less heat coming from the vents.

TexasSeville: Does the above added info cause you change or modify your diagnosis of a short in the system?

Also, any comments on possible filmed-over dash sensor?

This one has me pulling my hair. The car is four years old, but only has 23k miles on it -- and drives beautifully. Since it's only recently out of factory warranty, I hope the dealer fix won't cost an arm/leg, or they'll not charge me because this problem was reported a few times in the past, which they couldn't duplicate, therefore didn't do anything to fix it.

Best regards, Jack M.

The sensor on the dash is for the twilight sentenal, it senses light and turns on your headlights if it gets too dark. I don't think that it is a temperature sensor problem, it sounds to me more like a problem with the climate control switch. Could be loose wire, dirty contacts, grounded wire. Does it only do it right after you have adjusted the desired climate temperature? could be a sticky contact in the switch... :hmm:

The sensor your looking for is that little thing right under the dash pad, above the wood grain, about the middle of the dash. I always wondered what it was till I read about it in my factory service manual....