Grand Cherokee HeaterTreater Fix

First, to understand the solution, you have to understand the problem. When heater control went from the familiar slide lever with a cable connect to electronic control, there was a need for a way to modulate door position just as we used to do with the lever. What Chrysler came up with was a “poor man’s” stepper motor. The system detects the endpoints and can control position by running the motor for the percent of the cycle time between endpoints to hit the right spot. As with all stepper motors, the trick is to find the endpoints or extents of door movement.

This can be done with a mechanical switch, magnetic switch, optical system, etc. The method chosen by Chrysler was to run the motor until it hits a stall point and sense the voltage surge that indicates that the door has reached the full extent of possible motion. This would have been just great except for two problems. 1) The software guys never believe the hardware guys and wrote the program to go through the calibration routine of detecting the endpoints to initialize the system every 20 times the engine is started. 2) The components are plastic and cannot take the repeated force of calibrating the system over time. The fail mechanism is not a function of age, mileage, or driving habits, but just how many times the car is started. If you run 10 errands a day, the failure will occur sooner than someone that commutes 200 miles, but only starts the car twice.

The GC is designed with a limit pin molded into the axle like a “Q” that is limited by two points molded into the heater box. This pin is undersized and is the first thing to break. Once the pin is broken, the calibration forces are transferred directly to the blend doors(and re-circ door), and the doors themselves will break over time. The failure is simply a wear-out mechanism and will occur on all GC’s given enough time.

Once the doors break, there are two basic ways to address the fix. 1) replace the doors with stronger components that can withstand the forces OR 2) reprogram the computer to calibrate less frequently. Note that this doesn’t actually solve the problem, just delay it out in time. If it took 40 yrs for the system to fail, no one would notice.

Chrysler chose a solution midway between the two basic fixes. The factory fix is to replace the plastic axle with a new axle that has a thicker limit pin. This thicker pin requires that stop points be molded into the heater box to allow the same extents of motion. The fix requires replacement of both the doors and the plastic housing. The system will still break over time, but the intention would be for it to last long enough that it will fall off the Chrysler radar screen. If you check some of the forums, you can find multiple examples of GC owners that have replaced the doors more than once.

We at HeaterTreater have addressed the problem by constructing metal components that are engineered to withstand the forces for the life of the GC. We have two blend door products. One that can be installed through the glove box with a simple cut into the housing, and a second(HeaterTreater Pro) that replaces both axles on a Limited model and maintains dual control. The problem with the pro is that you have to completely disassemble the dash and remove the heater box to get access to the passenger side actuator motor that is buried behind the box, just like the factory fix. This product maintains dual control, but is significantly more difficult to install and we have found that most customers elect not to go to that much trouble unless there is also a need to replace the heater core or evaporator. The simple fix is a compromise between cost and functionality. Easy fix/single control vs difficult fix/dual control. We have found that with a 5-10yr old automobile, most are choosing the cheaper labor costs of the easy fix.

One of the comments was that the goal should be to do the “correct” fix. I fully agree with that. However, my definition of “correct” is to do it once with components that will last for the life of the GC. Whether a customer chooses a low cost fix that gives up dual control, or undertakes the more extensive process of removing the heater box, the HeaterTreater is a one time permanent solution. With all due respect, the HeaterTreater is the “correct” fix.

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