93 GC heater/ AC fan on all the time problem

Everything seems to be controlled by the PCM module, which is the large computer under the hood, bolted to the firewall on the passenger side. You should be aware that your vehicle has extensive built-in testing capability, especially for the HVAC system. You should really run through all the tests to pinpoint where the problem is before you start replacing things. It's more than I can give you here. I recommend you get your hands on the shop manual. There are 7 pages devoted to these tests.

Dick

Walt Barie did pass the time by typing:

Yep. More than likely the power module.

You can pull Fuse 11 (30A in the distribution center behind battery) And that will remove power to the system.

Run the ATC diags.

- Turn the key to ON

- Depress A/C and RECIRC at the same time and turn the temperature knob one click to the right.

- Keep holding the A/C and RECIRC buttons and all the stick figure lamps will light up (lamp test)

- Release the buttons.

- Push either A/C or RECIRC once

Record the numbers that display.

There are other tests that can be done from the buttons but for now just stop the test by turning the key off

I'll scan the pages for you but it will be later today. Gotta go to work.

I ran some basic diagnostics on the Climate control module and it checks out ok EXCEPT the module does not get the correct fan feedback speed and it can not control fan speed (i.e. the fan runs at the same speed no matter what speed I input in test mode).

In the '93s it does not appear that the main body PCM module controls the fan. There appears to be a separate fan control module hidden somewhere under the dash that receives its command from the climate control module.

W.B.

The only thing I see between the Controller and the fan motor is something called a PWR MOD. The way it is drawn it looks like an integrated circuit. I think an A/D converter. However, the blower drive coming out of the controller on C9 shouldn't be calling for the fan to run when it shouldn't be. I still suspect the controller. It is subject to failure if you get water in that 60-pin connector.

Dick

Dick did pass the time by typing:

The PWR mod takes a signal on the Brown(yellow stripe) wire from the HEVAC controller, Pin 9. It's basically an SCR or power switching module.

Have you checked the blower-high relay to see that it isn't stuck?

Don't exactly remember where that realay is. Think it was down by the module wrapped up in tape. It's been a while and my ZJ doesn't have the automagic climate stuff.

Which brings me to a basic question. Where is the so called Fan Power module located????

DougW wrote:

OK found it. Thanks

L.W.(ßill) Hughes III wrote: