Heating problem with 2003 Jeep Grand Cherokee Laredo

I have a 2003 Jeep Grand Cherokee with a heating problem. I have checked the blend doors and the recirculation door they are fine and the motors that drive these units are good. The problem isn’t in the ductwork. I am leaving the HVAC setting on hot all the time and the fan on low. When I start with a cold engine and drive it, warming it up to about 200F I get nothing but cold air. When I shut the car off and come back after any period of time (the engine temperature can drop considerably) and I start the vehicle I have heat instantly. This pattern is consistent. Also when I initially shut the engine down (still no heat) both incoming and outgoing heater coil hoses are hot, so I am getting flow through the heater coil. On restart I have heat. Any Ideas? Thanks, Jeepster.

Automatic temperature control or manual? Unless your blend door assembly has been replaced I would suspect that is the problem. I have replaced dozens of them and they tend to flop around after the shaft breaks causing full hot or full cold at random.

You can try disconnecting the battery for a few minutes, the next time you start the vehicle the ATC system may go though a self calibration. If that doesn’t work next would be to hook up a scan tool, perform the calibration process and read the fault codes. The cooling system is full isn’t it?

I have manual temperature control. The blend doors are o.k. the shaft only rotates about 45 degrees (guess), and it seems to be spring loaded as it snaps back open pretty strongly. Operation of the doors seems pretty smooth. I think this is a replacement box as the stop is pretty beefy. I just bought this car and it seems like the more I drive it the better the heater is working. The cooling system is full, but I think a lot of work was done to the car before I got it. I’m kind of suspecting a flow problem in the heater core. What is the ATC system? Are there any temp. sensors,relays or computer chips associated with the operation of the heating system? What would I hook the scan tools up to? I drove the car today and the heat actually began working as the engine heated up, I drove about ten miles (good heat) but I stopped (shut the engine off) and came back about 15 minutes later and didn’t have any heat (engine temp was 190F). I drove another five miles without heat, left the car for about an hour and a half. As soon as I started the car I had heat (engine temp. was probably 100F at most). I’m flying by the seat of my pants here. Thanks for the input Nevada. Keep the ideas coming. Afterthought, will leaving the blend doors in the closed position (on hot) in the position that puts pressure on the spring be detrimental to the blend doors or axle?

I think there’s a good chance that you just have some air bubbles floating around in there & occasionally getting hung up in the core.

Get the front end of it up in the air so the radiator cap is higher than everything else & run it for a while. If the engine’s hot you can just run it as is & any air should end up going through the overflow. If you’re going from cold, maybe pull the cap & run it for a while.

The blend door actuator is the one accessed through the glove box. If you are experiencing erratic behavior from the temp control it is usually a fault with the feed-back strip (position sensor) in the actuator. This can be tested with a scan tool (dealer). When the temp is stuck on cold remove the glove box and check the operation of the actuator. A new blend door actuator is $50 online.

If you think this is a cooling system problem open the hood and feel each hearet hose, they should both be hot (one not as hot as the other).

ATC is automatic temperature control, digital display and dual zone.

Nevada, Yes I accessed this through the glovebox. Is the actuator the motor that turns the shaft? If so when I first checked it , it wasn’t working. I disconnected it from its power supply and took it apart. There were two copper strips that rotated with the gears on the bottom of one of the shafts of gears. Are these strips the position sensors? They appeared to be worn . When I put things back together the motor worked. I thought that the unit had reset itself after being disconnected for more than 30 seconds. I also felt that the motor had been shut down because of some kind of fault in the system. Could the motor need to be replaced? Also, I don’t have ATC, I have a single zone control with no digital display. Could there be some wiring issues here (hope not)? Both incoming and outgoing hoses from the heater core are hot. Maybe the motor and air bubbles are contributing factors.

The most common error code with this symtom is “open circuit in blend door feed back circuit”. Wiring or connector problems are unlikely, the actuator is usually the problem. The actuator is the motor assembly that moves the blend door shaft.

There is nothing special about purging the air from the cooling system, once the thermostat opens, the system is refilled and the engine is run at 2500 rpms for about 30 seconds the air will be forced out of the heater core.

I think you are right about the actuator. Keep in mind I have had the controls set on hot for several days and haven’t been opening or closing the blend doors. Things are getting better the more I run it, but I’m not quite at 100%. Are the copper strips I mentioned the position sensors? Also, where can I find the actuator on line?

There are a number of dealers with online catalogs. I have used this dealer; http://www.moparonlineparts.com/

Thanks for the help guys. I’m glad I tried this site it has really helped. Once again, will it hurt the blend doors or axle by keeping the temperature setting on hot with the pressure on the spring mechanism at its maximum until I get the new actuator (or for a month or so until I get the money)? Thanks again.

It is normal for the blend door to be positioned at full hot or full cold as long as the motor isn’t trying to rotate further due to the failed position sensor. As you observed there are stops in the housing to prevent over rotation of the shaft. If you feel something may become damaged, rotate the temp. control a few notches from full hot and disconnect the motor until you get a replacement.

Is it o.k. to disconnect this motor while the power is on or will it cause problems?

I’m back. I put in a new blend door actuator, and the problem persists. It will go to hot and then back to cold. It is like something is telling the actuator to reverse direction from time to time and open the blend doors on its own. I can manually reset it to hot and get hot air for a while and then it goes back to cold. Then if I play with the mode dial I can get hot again. I can have the settings on hot and when I start it I get cold air no matter how hot the engine gets, not touch the settings-park the car for a while and when I restart I have hot air. It is like the system is resetting itself every time I start the car. It is worse with the new part than it was with the old one. My dealer wants $115 to just diagnose the problem, and the $115 isn’t applicable to the repair bill. I’m beginning to think this is an electrical problem, I don’t know where to go from here.

If you haven’t checked the connections to the actuator motor you should do that and make sure there isn’t a bad connection somewhere causing this trouble. I sounds like either a controller problem or bad connection to me.

It would be money well spent if you purchased a factory service manual to help you with this trouble. You can also purchase a trouble shooting manual that will help you locate the problem. Even if the manuals cost a couple of hundred dollars it is a good investment in my opinion. Check Ebay for some good prices.

O.k. I’m back with the answer. The HVAC Control head was dying and finally went out completly. In the end there was no power going to the actuator from the control head, but there was power coming to the control head. Thanks for all the help guys.