Jeep Grand Cherokee '98-'04

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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.

If you feel uncomfortable installing the repair yourself, go Here to find a HeaterTreater certified garage near you.

Jeep Grand Cherokee '98-'04
Jeep Grand Cherokee '98-'04 HeaterTreater Jeep GC NEW Part 1


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.

Click Here to See Jeep GC Installation Videos

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

Click Here to See Re-Circ Installation Videos

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 a video guide to diagnosing and installing the fix.

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.

The Pro is for advanced technicians and involves the removal of the dashboard and steering column. It’s only recommended if you already plan on replacing your heater box and your AC evaporator. You can replace your Re-Circ door as well.

The repair will take 4-5 hours and Mechanical skill ARE recommended.

Aluminum vs Steel air doors

We are the industry engineering experts on air doors and have been in business over ten years with multiple vehicle application.  Early on we evaluated aluminum doors and found some obvious and not so obvious issues.

-  Aluminum would appear to be lighter and less stressful on the actuator motor...not true.  As we all learned in Kindergarten physics, if you have a fat guy sitting in the center of the see-saw, it doesn't have an impact.  Rotational stress is a function of distance from the axis.  Our doors are heavier, but the bulk of the weight is in the axle which has no impact on required torque.  In fact, the added axle weight actually stabilizes movement.

-  The actuator motors have waaaay more torque capacity than required for this application, and actually is the root cause of the common failures.  We've been doing this across multiple models and have never seen an issue with motors wearing out or breaking with steel doors.

-  Welding aluminum plate is problematic and we saw issues early on with doors breaking at the periphery of the weld pattern.  Aluminum plate changes physical characteristics from the extreme heat associated with welding and becomes weaker at the weld point.  This is why aluminum plate is riveted, not welded on airplanes.  Welding is OK on aluminum structural components that can withstand the heat, but not plate.

-  Aluminum is "springier" than plastic and can vibrate in the air flow producing a humming noise.  It's generally not an issue or even annoying, but the resonant vibration can further weaken aluminum welds.

-  Our steel plate is more rigid and gives a more reliable and consistent seal against the extents of movement.


We’ve seen comments that my plastic door lasted 10yrs or more and I”ll just replace it with another plastic door and get 10 more years of service.  On the surface that sounds logical, but it’s not quite true.

The failure is due to the weakness of the plastic door and the torque applied by the actuator motor during the calibration process which is an automatic function that can’t be controlled.  The original battery in the vehicle was the minimum that the supplier could provide and lowest cost.  You never see a Ford advertisement that says “buy our vehicle because we use better batteries than Chevy”.  However, aftermarket battery sales companies want to provide a battery that will last longer and perform better since they have to stand behind their product.  It’s common to go from a 55CCA OEM battery to a 70CCA replacement.  You’ll notice brighter headlights, quicker starting, more start power on those cold days, and power windows that go up/down faster.

This impact also shows up on the torque applied during the HVAC calibration process and will break a new plastic door much faster than the original door.  The calibration is a function of on/off cycles of the engine and depending on usage, expect a replacement door to last only 12-18 months.  Even a metal connection on the replacement air door to the motor will fail because the plastic stop points on the box will break, transferring force to the plastic door again.  Our metal doors replace all the plastic components with steel and the doors are strong enough to withstand any forces that the system applies and will be a permanent fix to the system.  

If you are selling the vehicle and just want it to work long enough to get rid of it, cheap plastic is a viable solution.  If you need longer term performance, steel doors are the way to go!!

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