Step Two: Understand The Problem

Failure of your heat and/or A/C in your Jeep Grand Cherokee is due to the failure of your blend door.

Heater Treater replaces the cheap, plastic blend door with steel. Replacing the blend door with the same plastic part from the manufacturer WILL result in continued problems — the same system design problem that caused the failure in the first place WILL happen again.

Heater Treater attacks the root cause of the failure by constructing hardware that is designed to meet the rigors of normal operation of the HVAC system, and last for the lifetime of the Jeep.

Important! Heater Treater offers multiple fixes for the Jeep Grand Cherokee. Please read the information below carefully to figure out what solution your vehicle requires.

First, you must determine which system on your vehicle needs to be fixed. There are three possibilities. Please note that it is possible that BOTH your blend door and re-circulation doors are broken. Be sure to check all of the instructions listed below.

1. Single Zone Blend Door
2. Re-Circulation Door
3. Dual Zone Blend Door (Separate temperature control knobs for passenger and driver)

Single Zone Blend Door

The blend door failure is not as common on the Laredo as the Limited, although it will happen, it just takes longer. Single Zone refers to one A/C and heat control for the entire vehicle. If there are separate temperature controls for either side of the vehicle, then you have a Dual Control Blend Door and need to follow those instructions.

Diagnosing the Single Zone Blend Door:

• You can physically check the operation of the blend doors by fully swinging out the glove box. There are two removable rubber stops at the top of the box opening and in early models, a dampener arm on the right side of the box (they took them out in later models, and I’d suggest that you do the same).
   
• With the glove box open, you can see the blend motor to the left of the opening. The motor should move when you change the temperature setting. However, failure to move does not indicate a bad motor. The computer will shut the motor down if it detects a system fault. Either way, you need to remove the motor and check the axle before any diagnosis is possible.
   
• The motor is held in place with two Phillips screws. Disconnect the wire, remove the motor and you will see a plastic axle that is connected to the blend doors. The axle should have a limit pin on the white plastic axle (like the comma on a “Q”) The GC failure occurs because this pin breaks, transferring the force of the motor directly to the blend doors. When this happens, it’s just a matter of time before the doors break. Check for a broken limit pin on the axle and check that you can turn it ~50 degrees of movement between the two stop points.
   
• Start the GC and turn on the AC. You should be able to manually switch between heat and AC by turning the axle with your fingers.
   
• If the motor is spinning and not stopping, or the blend doors are not switching between AC and heat, your blend doors are broken and the Heater Treater Blend Door Fix is the answer.
   
• If everything is working properly, the blend doors are not the problem. In that case, you’ll want to check the re-circulation door below.

Re-Circulation Door

The re-circulation controls whether external air is pulled into the fans or internal air is re-circulated. When the re-circ door fails, air enters through the external vent and blows straight out the internal intake. It’s like having a window open all the time. The second most common fail is for the door to break off completely and fall to the bottom of the box, blocking the fan intake. When this happens, you will generally have greatly diminished air flow and the characteristics may change if you hit a big bump, randomly bouncing the broken door around.

• The simplest way to diagnose the problem is to turn the AC on with the fan blowing at the highest possible setting. On the outside of the car, check the air flow into the intake vent between the hood and windshield, between the windshield wipers. When the re-circ button is off, you should feel/hear air being pulled into the system. With the re-circ button on, there should be no air flow. If the system behaves the same with re-circ on or off, you most likely have a problem with the re-circ door.
   
• If the air flow test is inconclusive, you can also remove the glove box and see the re-circ box in the upper right hand part of the opening(use the picture as a reference). You can see inside the box with a flashlight and watch or feel for any door movement when turning the re-circ button on and off. The re-circ door should seal against the internal grate when on (don’t get your finger caught by the door closing…it hurts).
   
• On the Limited model, you can also read the AC fail codes to check for failure. With the AC on, hold down the AC and Re-circ buttons simultaneously, and turn the drivers side temp control one click to the right. Fail codes should flash on the screen if there are any problems. If your AC codes read any combination of 19,20,51,52…this indicates that the re-circ door is broken.
   
• Note that the re-circ door can fail independently of the blend door. So make sure you still check your blend doors for failure.

Dual Zone Blend Door

Heater Treater’s Dual Zone Blend Door fix is for Grand Cherokee Limited’s with dual zone temperature controls. You can read the fail codes on the system by following this procedure:

• Turn the ignition switch on and turn on the AC system. You should see a temp display for the two sides.
• Simultaneously hold down the AC and re-circ buttons while turning the drivers side temp control knob one click to the right.
• This puts the system into diagnostic mode and you should see a zero for no codes or if there are problems, one or more of the following codes. The higher number code is an historic fail code and the smaller number a current fail code.

15, 47 – Left temperature door not responding

16, 48 – Right temperature door not responding

21, 53 – Left temperature door travel too small

22, 54 – Left temperature door travel too large

23, 55 – Right temperature door travel too small

24, 56 – Right temperature door travel too large

20, 52 – Re-circ door travel too large (check our re-circ door listing)


54 and 56 are the most common fail codes and indicate a broken blend door. The system may still be marginally functional, but it will totally break soon. If any of the codes are present, the Heater Treater is the solution.

We have three different kits for repairing the dual control.
1. Standard Heater Treater. This kit is the least expensive and easiest to install. It converts the system from dual control to single control by connecting the blend doors together and operating from the driver’s side temperature control knob. The passenger side still displays a temperature and will “adjust”, it just doesn’t do anything. The passenger will usually never know the difference. This kit is correct for either the single or dual control systems.

Click Here for Standard Heater Treater

2. Heater Treater PRO. This kit requires removal of the plenum box and generally customers use this if they have to remove the box to replace the heater core or AC evaporator core. It’s basically just a duplicate of the OEM doors, only metal that won’t break again like the plastic doors.

Click Here for Heater Treater Pro

3. Heater Treater Dual control through the glove box repair. This kit adds an actuator motor “piggyback” on the existing front motor to control the back passenger door. It requires a little more work and wiring to install, but will retain dual control if this is a requirement. Beware any solution that re-uses the back motor by just slipping onto the plastic drive axle. This little axle will not withstand the constant forces and will break off over time resulting in a bigger problem than the GC has now. More technical information is available in the TECH section at the top of the page.

Click Here for Heater Treater Dual Control