I have a 2001 jeep grand cherokee with heater problems. I can only get warm air when the control is set all the way to hot. I removed the glove box and removed the motor for the heater blend assembly and rotated the white control arm manually but still only warm air, could the plastic blend doors worn out or is the water core faulty?

in side the heater plenum behind the glove box i beleve

If the heater hoses are hot, the problem may be a faulty blend door under the dash. The blend doors direct air thru the heater core and the vents.

are you certain its the control knob ?? the heater may be bad...

you remove the part of the dashboard with the control on it, there are hidden screws i the glove compartment and in the pocket. Remove the pocket to reveal them. The rest are under the dash and under the rubber plugs if any).

once you have it dropped you can then replace the control unit.

Check that the Heater / AC Door Actuator Motor is actually functioning by selecting heat to vent and listen.

Make sure you have vacuum to your climate controls by selecting various air vents (upper/lower/face)

If the return heater hose is not warm also - then your heater core might be plugged up. A replacement heater core runs between $83 and $153 at NAPA depending on their mood when you price it. It is kind of a pain to replace you might want to have a shop do it.

Sounds like its the mixing door actuator motor. I believe its located behind your glove box, so if you remove your glove box you should be able to see it. Its a motor that actuates the mixing door to allow only hot, only cool, or a combination of the two into the vehicle. If you can get at it and the door seems to be able to move freely, you may want to check the heater control switch for voltage change using a multimeter. Im 99% sure it is one of these two culprits. Either the actuator motor or the switch. Good luck!

You have the blend doors problem which needs to be fixed. At jeep it is about £1300, by EDM in bicester it is £255 and maintains dual control. I would imagine the recirc dooe is or soon will go as well.

this sounds like the recirculation door in the heater box is broken and this is a difficult and can be an expensive repair as the dash has to be removed for access. a quick check for this is if you release the glove box and let it hang you will see the heater box if you reach up to the left top you will feel a grid and the recirc flap is housed there you can operate the blower and hot and cold and see if flap moves

there should be a small valve attached to a hose coming from the engine into the firewall this valve directs the hot engine coolant into the heater radiator in the heater box it probably is closed open it and, you should have heat then: it should be easy to find the reason it was closed

I purchased a Blen Door repair kit. for my 2002 Jeep Grand Cherokee after having only cold air blow out of the passenger side for over a year. I found it on EBay. It requires you remove the glove box, cut open the heater box and replace the blend door. I really didn't want to cut that open, however, with the tape that comes with it, I have had no problems with it leaking any air. The dual control no longer works, the temperature is now completely controlled by the drivers side, but to save $1200, I was willing to do this. I have taken the entire thing out before to replace the heater core, didn't want to do it again.

The blend door on the passenger side has broken. Jeep has made a replacement section for the heater box assembly so you don't have to buy the whole thing. You will need to remove the heater/A/C box to replace the part. I have done quite a few of these repairs to fix the problem