Air Conditioning problem
1998 Chrysler Concorde 6 cyl Front Wheel Drive Automatic 128000 miles

For the last several years, my automatic temperature control has slowly been losing the ability to maintain temperature.

It started with erratic fan speed. With everything working correctly, temp at 73 degrees, all of a sudden the fan would go to full speed and the temp would go full hot or full cold. Sometimes it would only be a temporary problem and then work fine for another few weeks.

Eventually, it became so much of a hassle that I just started using the manual mode for operation.

A few days ago, the fan went immediately to full speed and hasn't responded to any manual attempts to adjust the speed. Even with the system selected to "Off", the fan runs at full speed.

I've had the car to the dealer twice, a general automotive repair shop once, and to two A/C shops. Each time, they say that they can't find anything wrong with the system, meaning that the system is not setting any fault codes.

I've tried the process of resetting the A/C system using the buttons on the temp controller with no luck.

I know that the components of the A/C system are actually controlled by the Body Control Module, with input from the temp controller. I really don't want to just start "shotgunning" the process by replacing parts until I stumble into what is wrong.

Suggestions...???

Thanks,
Bill

Hello – just a couple of things you might check/try. First read the info on ATC In-Car Temperature Sensor and Ambient Air Temperature Sensor. Me I would first do the check on the sensor motor fan, I have attached that. I don’t believe it is the thermistor in the ATC only because it says it should be throwing a code. You said the dealer/shops don’t see a code. I would next, go ahead and replace the Ambient Air Temperature Sensor (I have attached the pics where it is) mainly because if the sensor motor fan inside the car is working after the test, the thermistor appears to be working (no codes) the Ambient Air Temperature Sensor “…is used by the ATC system to adjust blower speed, temperature offsets, evaporator temperatures and mode control.” This seems more like what you are saying. Plus it is only about $17.00 by my info at the dealer, part number 4688204. You might check Auto Zone, O’Reilly’s etc also. Good luck and be safe.


ATC In-Car Temperature Sensor
The Automatic Temperature Control (ATC In-Car Temperature Sensor returns electrical signals to the Body Control Module (BCM). The In-Car Temperature Sensor is used on ATC equipped vehicles only. The In-Car Temperature Sensor is made up of two parts. One part is the in-car sensor motor fan assembly and the second part is a temperature thermistor. The in-car sensor motor fan assembly attaches to the back of the ATC Control head. This assembly has a small fan and a motor which draws air through the intake on the front of the ATC control. The in-car sensor thermistor is located inside of the ATC Control Head. Air drawn from the passenger compartment by the in-car sensor motor-fan assembly, flows over the thermistor. The in-car sensor thermistor changes resistance with air temperature. The BCM measures this resistance and calculates the temperature of the air drawn into the ATC Control. The ATC system then makes adjustments to maintain the optimum passenger compartment comfort. Refer to the ATC Sensor Motor-Fan Operation table for when the ATC Sensor is operating.

The in-car sensor motor is a separate serviceable part connected to the ATC Control Head. See Diagnosis and Testing for proper check of airflow. The in-Car Sensor Thermistor is part of the ATC Control Head and not a separate serviceable part. One must replace the ATC Control if the ATC self-diagnostics indicates a fault code.

Ambient Air Temperature Sensor

The ambient air temperature sensor is located on the inside of the right front bumper beam. This sensor will inform the ATC system of the ambient temperature outside the vehicle. This sensor is used by the ATC system to adjust blower speed, temperature offsets. evaporator temperatures and mode control.

The ambient sensor is not serviceable and must be replaced if found to be defective.

The ambient temperature sensor is used on all LH vehicles with or without ATC systems.


In-car sensor motor fan test
1. Perform air flow test to check motor/fan assembly.
a. Turn ignition to the ON position and push the OFF button to stop the ATC system airflow. This will make it easier to observe paper in the step Step
b. Place a small piece of newspaper in front of the sensor/motor opening on the ATC control. If the paper sticks to the opening, the In-Car sensor/motor is operating properly. The piece of paper should be only large enough to cover the grille opening.
2. Check if the electrical connection and connector are OK.
3. Check for the two foam seals and their condition, it is absolutely necessary for proper sensor operation.
a. Seal on the inside surface directly behind the nameplate.
b. Seal (strip) located directly to the right of the right center duct opening (instrument panels with trim bezels).

OUTSTANDING REPLY...!!!!

Very good analysis and suggestions. I'll be working on these over the next several days. Where the front end sustained major damage several years ago, I'm suspecting the ambient air temp sensor.

I'll let you know what I find.

Thanks for the great service...!!!

Bill

So far, I've verified that the in car sensor motor and fan are drawing air in through the intake.

I'll take a look at the ambient temperature sensor as soon as I can crawl under the car and locate it. Is there any testing that can be done on the ambient sensor, such as resistance tests with varying temps...???

Is it possible to verify that the trim around the ATC head is only held in place with a few screws in the lower area...??? Once those are out, I'm guessing the trim should be easily removed and the ATC head can be worked on.

Thanks again for your help..!!

Bill

Hello Bill
As for the trim, I have attached pics. It appears to be held in with clips. It always makes me nervous to pull on the plastic parts etc as it is hard to tell at times how it is held in. You might ease a flat tip screwdriver along side and gently pry. Not to small as it may chip. You might put a rag between the screwdriver and the dash to prevent any damage. Some are held in with screws once you remove the ash tray or other surrounding items. But if you look at the pic, it doesn’t look like it. Then the next pic shows the back of the panel, removing the plugs. The screws hold the control unit in. You might consider calling the parts department and see if you have to order screws or clips for it. That would be a sure thing. Me, the less you remove the better. I would still just replace the sensor at the front of the car since it is inexpensive. I don’t show a check for that though there may be one but if it is intermittent it may check good and then bad on the car. Again, it’s the least expensive and so far your check of the ATC shows it is okay. Not sure if this helps……..hope so. Good luck.

I've located and removed the ambient temp sensor. Interestingly, that had no effect on the operation of the blower speed. That could indicate the sensor is open, resistance-wise. I haven't had the time to test it to see what resistance might be there.

I've also managed to remove the trim and look at the ATC head. All appears to be okay in that department. You were right; it IS scary pulling on the plastic. Once I got it out, I can see that it's not that big a deal for future work in that area.

Tomorrow I'ill buy the ambient temp sensor and replace it. With luck that will be the culprit....

Again, thanks for your excellent advise and guidance.

Bill

Bill - if you have time please let me know if that fixes the problem........also............me, since that part plays such a big part in the operation of your AC, even if you could get it from a parts distributor, I would get the OEM from the dealer especially since it is not that expensive. Good luck.

Good afternoon....

Well, I purchased an OEM ambient temp sensor and replaced it. No change in the symptoms.

As part of trying to get it working, I started trying to use the "Auto" mode. I was able to get it into the auto mode for a while and could feel that it was regulating the temp to about what was set on the ATC head. But, it was still in the high speed mode for the blower, which I believe was causing it to "hunt" the temperature a little bit.

Subsequently, the ATC head dropped out of the auto mode all by itself. I now recall that the ATC head really doesn't want to work in auto at all. Most times, it ignores any attempt to select auto. Most components seem to be doing what they should, such as the temperature blending valve and the various distribution valves. The parts that are not cooperating are the blower (speed) and the auto temp operation. One indicator might be the failure of the selected temperature to be displayed most of the time.

I used to know how to run the self diagnosis on the ATC head, but have lost the procedure. Do you know how to do that test...???

I'm now quessing that the ATC head might be next in line for replacement. I've been told I can find one at a "Pick Your Part" lot for about $50.00.

Thoughts...???

Thanks for sticking this out with me...!!!

Bill

Hello Bill,
I see this wants to give us a hard time huh. I only have a few minutes right now but will check back later. If possible can you do this, first, let’s make sure we are with the right engine. I show two V6 choices. V6-2.7L VIN R and V6-3.2L VIN J. Which do you have?
Next, have you stopped by Auto Zone or O’Reilly’s and had them check for any codes? It’s free and that would tell us that is clear. Remember the ATC is supposed to throw a code if not working.

Last, if you haven’t driven the car since putting the sensor in, please do so about 3 miles at least. For that matter you will I guess to check the codes.

Let me know and I will check back shortly.

Bob

Thanks for the quick response, Bob...

It's a 3.2L.

More info.... I actually removed the temp sensor last night in preparation for getting the replacement this morning. SURPRISE...!!! It really didn't like that... When I drove the car this am, I had a Check Engine light and the battery annunciator illuminated...???? In any case, as soon as I got to my first desination, I replaced the sensor and the battery annunciator went out. The check engine light stayed on until after leaving the second destination where I installed the new sensor.

I have a OBD II tester at home and will check for codes there.

Gotta run home... wife just told me her battery is dead.....

SHEESH...!!!!

Thanks,
Bill