Hi there. I gave just fitted a new heater fan blower controller after the old kept blowing fuses but I have a problem in that the fan will not switch off. Even with ignition switched off. I think it may be the new unit. But any one hit this before.

Any help appreciated

Cheers Paul Compton.

 

More info needed

 

Hi there what info do you Need? It's a 2001 jeep grand cherokee the old unit was blowing fuses it looked like before I had it it might have cooked and was repaired.

I brought a new resistor unit and refitted that. As soon as I plugged the fuse on the blower came on even though the hearer unit and car were not switched on.

Come back to me if you need specific info. It's got me totalled foxed not sure what to look at next.

Thanks for your reply.

Paul

 

Is it the single zone manual control or the auto temp control heater? Was the terminal plug fried? Did you replace the heater control panel or just the resistor?

If it's the manual heater control I know pretty much everything about it, but am clueless with the auto control unit. I'm going to look at the circuit diagram.

Okay, only the manual heater has a resistor. The blower motor is supplied with constant voltage and the speeds are controlled by a selectable ground path thru the speed switch in the panel. The speeds are controlled by grounding different taps off the resistor. In other words there is a short to ground somewhere in the wires to the speed control switch so it runs on high all the time. This ground path goes thru the mode control first so the blower doesn't work if the mode control is in the "off" position. I would pull out the heater control panel and look for a grounded wire to the mode control. That's the one that sends heat to different places.

 

It's the auto zone control I only replaced the resistor everything else seemed OK as far as I could see. Basically fan stopped working so I put it down to the resistor.

 

In that case, you don't have a resistor but a power control module in the same place. The blower speeds are controlled by the logic circuits in the panel sending pulses to the control module. Your problem is you should have a power module in there instead or a resistor!

 

sorry Dave showing my ignorance I expect; I only call it resistor module as that is the name I've seen on here it is contained in a box as per the attached photo.




Module under passenger side glove box.

 

Okay, so you've got the right module. Now the problem must be in the heater logic. Great! This is a job for a geek! Sorry, electronic tech. The logic is supposed to give infinite speeds, like a volume control, by pulsing the power to the fan motor. Actually by pulsing the ground path. You obviously have a direct path to ground so the fan runs continuously.

 

Thanks for that Dave I have a new module coming just encase the original was faulty other than that I can think of nothing more.

 

Hi Daventry just for your information the brand new module I brought was indeed faulty and the new unit sent out was perfect heat again yahoo thanks for your help again.

 

It's good to know I've still got it! It may take a while, but I'm a pretty good diagnostician. Actually, I have the Full Service Manual to thank for this one! If you're interested, you can download one from pacificcoastmanuals.com for $7.99+tax. It's 93mbs of pdf files and the most through and concise manual I've EVER seen for a specific year jeep. You may also want to check out wjjeeps.com for other interesting stuff. One thing; DO NOT try to print out the whole manual! It'll take a ream of paper and a couple of ink cartridges to do it. There's 150 pages just on the transmission!

 

They look good manuals thanks Dave. Think one will be coming down my way.