HappyTrails

Dug a body control module out of a like 97 Laredo zj and the jy today. Seems the diagrams circulating around erroneously point to the junction block and not the BCM. They are close to each other, but the BCM is to the right of the junction block.

We are having a heater/AC operation problem. Its not the controls. Replaced that and found no joy. Fan works if power jumped to it. Fuses are all OK. Next is to swap the BCM. Heater controls have and connection to the BCM. Some how they are supposed to dance together, but are not.

This vehicle has the standard heat and a/c system, not the automatic temp control upgrade.

Has anyone solved a heater/AC problem by swapping a Body Control Module? Looking for some experience out there.

Thanks.

97 ZJ Laredo 2wd 6 cyl.

JPXJMOAB

Have you checked the wiring to the controls? It would be smart to check continuity.

HappyTrails

Yes. We spent a ton of time chasing down all these circuits and power etc. But there is some sort of interplay between the control panel internals and the BCM. The BCM is apparently source of lots of mysterious problems on this ZJ series. Thought this might just be one more of them.

dave1123

AFAIK, the blower fan on my 97 just used the switch in the heater control, the resistor, and the fan motor with power from a fuse. I don't understand why the BCM would be involved except for the dual zone climate control units.

HappyTrails

That was what we were thinking too. But the schematic shows a circuit to the BCM. Why I don't know. But the two connectors on the back of the heater control unit have lots more wires than just circuits to the resistor, internal lighting and a ground. Must be 15 wires between the two of them. And at least one goes to the BCM.

We are just glad not to have the automatic temp option. That I understand from threads here is a new level of problems.

97 ZJ Laredo 2wd 6 cyl.

dave1123

IDK if your 97's blend door is vacuum controlled or moved by STEPPER MOTORS like my WJ is. That would need BCM control.

In case you don't know what I'm talking about, stepper motor shafts will only move a certain number if degrees every time they receive a pulse from a controller. Say each pulse moves the shaft 1*, then in order to move it 40*, it needs 40 pulses. I've run into this concept in industry and in most cases, they are geared for the proper movement for each application. I was amused when I discovered they'd use to in the heater controls.

I also know the fan only turns completely off when the mode switch (vacuum) is in the off position, otherwise it runs on low.

HappyTrails

Blend doors are all vacuum. That control works just fine.

Still stumped.