This product allows you to maintain dual control on the Grand Cherokee dual zone control HVAC system.  All work is done through the glove box opening and disassembly of the dash and heater box is not required.  Like all the HeaterTreater products, the design is done by degreed engineers and thouroughly tested before release.  Please check our Heater Treater blend door listing for blend door diagnostic information.   

BACKGROUND

In the enclosed picture you can see a series of axles for blend door control.  The third axle is a new axle and if you look closely, you can see a limit pin that protrudes from the axle on the right.  The root cause of the GC failure is this pin breaking.  The pin limits the movement of the axle between two stop points molded into the heater box.  When the pin breaks, the force of the motor is transferred to the blend doors, and the plastic doors break.  If you replace the plastic door, it will just break again.

The next logical step would be to replace the plastic door and connect it to the axle.  The first axle in the picture shows what happens if you connect a stronger metal door with a set screw.  You wear a groove in the axle and again lose control.  If you machine a tight fit door connection to the axle, you get the result in the third axle in the picture.  The door no longer will break, but the axle itself has to absorb the torque of the motor.  The nylon axle is 5/16” diameter and if you look closely at the picture, it is hollow.  The axle twists off an will break after 3-6 months of use.  The fourth axle is out of a Ford F150.  This design does use the door to limit the movement of the motor and the axle is much thicker and made of a stronger phenolic plastic.  The Ford axle is designed to withstand the force, the GC axle is not.  The limit pin must be intact for the GC axle to keep from breaking.  If the door is broken, the limit pin is also broken and a stronger door will break the axle.  Additional information is available in the technical section of our HeaterTreater.net website.

SOLUTION

The HeaterTreater solution avoids the problems with the nylon axle by adding a second motor on the front of the heater box to control the back door (yes, the motor is included).   The second motor is mounted on top of the existing driver’s side motor and a separate axle is inserted through the first motor and attached to the back door with a set screw.  The two motors operate independently and will control the doors identically to the OEM system.  The hardware is shown in the pictures and an assembled unit is shown on a plastic blend door assembly that was removed from a GC.  The components are all metal and designed to withstand the forces in the GC control system. 

The motor used for the fix has been modified to limit the extents of door movement internal to the motor.   The force is absorbed internal to the motor and not transferred to the back blend door.  The system is not susceptible to the normal Jeep problems and will last indefinitely.  The operation has been fully tested with no evidence of any short or long term problems.

CAVEATS

The Jeep was not designed with this fix in mind and there are some issues with the installation.  The second motor, as you can see in the picture, is a tight fit and you have to wrestle it a little to get it in.  Not difficult, just frustrating.

The back of the glove box is molded to close almost directly onto the original motor.  The pictures show the original glove box shape and the modification that has to be made to allow room for the second motor.  If you look at your GC glove box, there is a rectangular box and it narrows on the left side of the box.  This was originally done to accommodate the actuator motor.  To accommodate the second motor, the box has to be modified further.  The picture shows cuts into the box and a patch that basically squares the box.  You lose a small amount of glove box area, but on my GC it was virtually useless anyway because of the shape.  The box in the picture used the cut-out portion to square the box and is held together with metal duct tape.  Depending on your concern with the appearance of the glove box, the fix could be done much more artistically.

The wires going to the back passenger side motor have to be cut, re-routed, and spliced into the new motor.  Full instructions and pictures are included.

SUMMARY

The original HeaterTreater single control fix connects the doors together and operates off of the driver’s side actuator motor.  This system separates the doors and maintains the original dual control functionality.  The single control fix is easier and cheaper.  Dual blend doors will take 1-2hrs of work and requires a Dremel tool, solder/crimp tools for splicing, and basic wrenches and screw drivers.  Full instructions with pictures are included and the fix is well within the capabilities of shade tree mechanics.  Technical support is available through email or phone if required.  Note that competitive products on Ebay rely on connecting the door to the plastic axle.  Our evaluations showed that this will not work in the long term, and when you break the back axle, the system has to be completely disassembled to correct the problem. 

The HeaterTreater solution is a reliable fix that will outlast the GC.  We stand behind our products and will make sure that any problems that come up are resolved. 

The dual control system is compatible with the original HeaterTreater hardware and we will upgrade previously sold product to dual control at half price.  Please contact us for full information.

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