Tech Runs into Problems Fixing Dual Temp Control

Posted 4/1/2009
By Bob Mordorski

It's amazing how many calls we take from technicians who have diagnosed a problem that should have been solved when the faulty part was replaced but instead, the symptoms haven't changed.

I recently took a call on a 2003 Lincoln Navigator with the dual automatic temperature control (DATC) system. The passenger complained that the right-hand (RH) side temperature control was not operating properly - it would not switch between hot and cold properly. However, the driver's left-hand (LH) side worked fine.

When working on an automatic climate control system, typically the first step is to perform the self-test and retrieve codes. To perform the self-test on this system using the DATC module, simply turn the key "on," simultaneously press and release the OFF and FLOOR buttons, then immediately press and release the AUTO button. In most cases, once the test is initiated, the screen will show a small moving cursor. At the end of the test, either a four-digit trouble code will be displayed or all segments will light up, indicating a system pass. Once the codes have been retrieved, pressing the front DEFROST button will clear the codes. After the test has been run and any codes have been cleared, recheck system operation.

Most auto climate control systems will not function properly once a trouble code has been set, especially codes pertaining to temperature blend door actuator operation. In this case, the self-test was performed on the DATC module and a code 2267 for the RH blend door actuator was received. After clearing the codes, the RH blend door actuator still did not work properly. Code 2267 continued to reset each time the self-test was run, even after replacing the RH temperature blend door actuator.

The temperature blend door actuators on this system have five wires each. Two wires are used to drive the motor in the actuator back and forth, and the other three wires are used for the internal position sensor. Just like a throttle position sensor used for engine controls, the position sensor in the blend door actuator has 5 volts feeding it, a ground, and a signal back to the DATC module.

On this system, the RH and LH blend door actuators share the 5 volts and ground to the position sensors. So, based on the fact that there were no problems with the LH actuator, the wires out of the module had to be OK. The tech checked at the RH actuator connector and found that the wires were good there as well. However, the output signal was not correct. The voltage stayed close to 5 volts no matter where the motor was, instead of sweeping from about 1 volt to 4 volts as the motor turned. To verify that the motor was in fact moving, a 9-volt battery was used to apply power and ground to the motor circuit. Once the motor moved in one direction, the polarity of the battery was reversed, which drove the motor in the opposite direction. This proved that the motor part of the actuator was good and would operate as it should.

Knowing the motor would move and also that there were 5 volts and a good ground to the position sensor in the actuator, the signal wire was checked between the actuator and the DATC module for any continuity to ground, battery positive, and to make sure that the wire had good continuity between the actuator and the DATC module.

The wires all checked out good, so the diagnosis was that the replacement blend door actuator was defective or possibly the incorrect one. The technician got another actuator from the parts supplier and performed all of the same tests but code 2267 would still not clear, and the voltage returning from the actuator to the DATC module still would not change as it should. I suggested the tech swap the RH and LH blend door actuators, since they appeared to be the same, and re-do the self-test. Now the LH actuator showed a code 2266. So knowing that there was nothing wrong with the DATC module or any of the wiring, the technician went back to the parts supplier yet again.

After a lot of wasted time, the tech found that the blend door actuators he was getting were in fact the wrong parts. With the correct blend door actuator finally in place, the codes cleared and the system functioned as it should. It just goes to show a new part does not mean that it's a good or a correct part.

Bob Mordorski is an IDENTIFIX Ford specialist. He is ASE master and L1 certified with nine years of diagnostic and repair experience.

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