99 Blend door and coupler

[DavidC]

I had the distinct pleasure of forging through this. There is very little info on this which prompts me to write this in case others have the same problem. The 99 FSM is wrong for at least some of us as it does not show the temp adust pot. BigPapa was instrumental by posting both the 1999 and 2k wiring diagram which clearly shows the pot. Apparently Dodge writers of the FSM think the 99 is vacuum. On to the problem. The temp control would only function on full cold or full heat. There was no middle ground, if you wanted cold I would need to turn the dial all the way to the left, if it was to cold adjusting the knob up made no difference, same with hot. I ordered the metal coupler thinking it could be cracked and slipping on the shaft. To get to this gem is another project. First you remove the sill panel then the kick panel. Next peel the rug back far enough to give some working room to get the rear screw out that some bright engineer put in an inaccessible place. I used a key hole saw (sheet rock) to cut through the rubber coated foam just enough to allow a 90 degree phillps screw driver to get that rear screw out a 1/4 of a turn at a time. After removing the 2 screws the motor will drop off the coupling. I had to remove the coupling which is pressed on the shaft with a pair of pliers and a small crowbar. Now I do not know if it was cracked but it was definately broken by the time I got it out. The metal coupling would not go over the door shaft all the way as they swedge it in 2 sides. Remedy for that was a dremel with a file bit until the coupling went on all the way. When it did not go on all the way putting the motor on resulted in the motor being cocked. Now the motor fun. I had it still connected electrically and laying on the floor. Turning the ignition to run and adjusting the temp to full cold and hot resulted in the motor running 360 degrees for as long as you wanted. Adjusted the temp incrementally had no effect as the motor did not run but would quiver like a landed fish at times. Started checking on a replacement motor and they are around $150. The 99 FSM is useless for this problem. I have a 2001 and looked up the blend door which stated to put the temp knob at the 12 O'Clock position when reinstalling the motor. Now heater treater has a few calibration instructions and one is to disassemble the housing and set a gear inside to the mid point. It's a little vague but I set it to that point. I reassembled everything, set the temp to 12 O'Clock then turned the ignition to run. I had marked the motor with a magic marker so I could see it rotate after installation. The motor stayed at the mid point then I went full cold which it did. So the motor knows where full cold is then I went full hot which it did. So now the motor knows both boundaries. I moved the temp knob between full cold and hot and the motor moved incrementally. Now this stepper motor has an electronic card and needs to be programmed (great, another electronic device) and apparently lost its programming at some time which gave me my problem. It is fixed right now but if it loses it's set points again it would require the motor calibration to center and going through the calibration mode again. If that happens a $ 150 motor will be in my future. I have no idea how it lost it's set points and it was a few years ago and I have just been putting up with it. The idea of documenting this is so that there is something out there besides the broken coupler threads.

 

[Joe Mc]

Boy sounds like you had a fun time of it

 

[DavidC]

Yeah Joe it was great . Not a real hard job but working in tight spaces with little or no information was the difficult part. I REALLY did not want to cut the floor and tried everything not to, I do not do anything to the body (drilling holes etc.) unless it absolutely needs to be done (one of my OCD things). The human body just doesn't bend around at 65 either so that didn't help.

 

[BRI7070]

I have this same problem and have been living with it for a year now. I will be doing this calibration procedure this weekend. Thank You for posting this procedure.

 

[petersonj]

It is fixed right now but if it loses it's set points again it would require the motor calibration to center and going through the calibration mode again. If that happens a $ 150 motor will be in my future.

I don't think the motor will lose its set points again. From what I understand the set points were lost due to an excessively worn or cracked coupler (interposer), so the motor travel limits were inconsistent resulting in the loss of the set points. Once you have calibrated the motor, the set points will be re-established when the blend door travels its full limits in both directions.

I replaced the coupler with the Heater Treater interposer in 2015 at 220,000 miles on the truck and I now have 330,000 miles on the heater controller and motor - 110,000 miles on the interposer and everything is working fine.

- John