KD3NE

Please read the entire post .......

1998 ZJ Limited
AUTOMATIC TEMP CONTROL - ( all electronic - no vacuum lines )

Problem - little to no heat.

Checked both hoses going to heater core, both are hot indicating to me water is flowing through.

HISTORY:

*This problem first occurred when I had an electrical problem that looked like a bad alternator. Replaced the alternator.

*When I got it back from alternator replacement I noticed little to no heat.

*Next day alternator "problem" recurred.

*Found battery connectors bad and replaced, no more 'alternator' issues.

*Heat began to come back, and I worked all the controls getting some of the heat back but never as hot as before the 'alternator' issue.

*Tonight the heat all but went away, after some fiddling with the controls - Fan Speed seemed to make the difference. My heat is back, but again still not as hot as before the initial alternator issue.


QUESTIONS:

Anyone have intimate experience working on this type of system?

Is there a Calibration Procedure that can be done within the vehicle itself or does it require some external equipment. ( shop told me the ATC systems have calibration )

I understand there is no vacuum operated parts in the system and that it is supposed to be a series of electronically switched motors or something like that. Any idea on what part *might* be failing?

THANKS

ol"blue

My'97 ZJ had the ATC system, and it had similar issues. Turned out that the temp **** goes bad, but can't be replaced separately. The whole control head has to be replaced as a unit, and it's pretty pricey. Hope you have better luck.
The 'ZJ ATZ has a self diagnostic system that stores trouble codes. You can access any stored when you follow the steps listed below, and the codes are are also listed. Good luck.

KD3NE

If it is the control head, I'll be lucky but I do not believe that to be the case.

I went to the dealer with the Self Diagnostic System codes that it shows and they told me .....

" those codes are no good, we have to run it on our own computer and that will cost you $100!!! JUST TO LOOK AT IT!


So here are the Self Test Codes ........

38 - Circuit was open ----> Blend Air Door Feedback Circuit

46 - Circuit was shorted ----> Blend Air Door Feedback Circuit

55 - Door travel range was too small ---> Blend Air Door Drive Circuit

56 - Door travel range was too large --> Blend Air Door Drive Circuit


What do you think????

Am I tearing out the dash to get inside ?????

ol"blue

I can't give an answer to that. I do know the Grand Cherokee's have a cheaply designed blend door system, that has been reported with many failures. Heater Treater has a fix for that issue, if that's your cause. Check this and see if it may be of some help to you. >->http://www.heatertreater.net/indextech.html#window

Willys55

you can reach the blend door through the opening for the glove box....remove the blend door motor and make sure you can freely "flap" the blend door back and forth...if you can, then the blend door actuator is bad....after you replace it, you have to do a blend door relearn.....simply disconnect the battery and touch the ends together to erase all stored codes and keep alive memory, then reconnect battery turn key to on but do not start the engine, the ATC will automatically begin relearn and in about 45 seconds it will finish...hope this helps.

KD3NE

Help me to understand this a little more.

I have removed the glove box and looking into it on the far right side I a can see a linkage attached to one door.

This door is activated by the FLOW CONTROL ****, by which I mean where you select how you want to direct the air - DEFROST - VENT -FLOOR and so on.

This feature WORKS ..... I can direct the air anywhere I want it, the problem is the air TEMPERATURE.

It won't get as hot as it should though it gets warm and on some days warmer than others.

Should I be looking at something else?

There is obviously a plastic 'wall' behind the glove box opening. I am not against cutting some of that away if need be.

THANKS !!!!!!!!



NOTE: The problem is TEMPERATURE control and NOT Air Flow direction or flow rate. The FAN SPEED and AIR DIRECTION seem to be working fine.

KD3NE

I now know that what I am looking at is the RECIRCULATING AIR DOOR and that is working.

Physically where are the BLEND DOORS in relation to that RECIRCULATING AIR DOOR ????

KD3NE

I found what I was looking for.

Though I have a 1998 model it is an early production model for that year and uses the same system as the 1997.

The people at heatertrear.com tell me that the couple is probably cracked/broken and I can get to the blend door motor without too much trouble.

We'll see how it goes in a few days!

ol"blue

Keep us informed.

Jcjunkie

Bump.
I perform the diagnostics and have number 49 number 58 and number 59.
There isn't much available telling me what that means...anyone have a clue?