malvarez10

Long time reader of this forum, first time poster. The Cherokee is a 1999. I have searched for solutions to this problem but have not found a resolution.
Symptoms:
Heater/cooler motor does not blow in any positions 1,2,3,4
I removed the blower motor and hooked it up to the battery and it spins FINE.
I have checked the fuses near the passenger floorboards and under the hood, none are blown.
The 2 prong wire that plugs into the blower motor has 12V on both leads!? (Is this normal?)

Confession:
I recently put a different radio in the dash. Easy install everything went well, except I forgot to remove the battery. Could this have fried my controller switch? I put the old radio back in and I still get no blower. This might be coincidence or just the fact that I havent tried to use the heat since last winter (AC wont hold charge). I checked for anything that could have come unplugged while working on the radio and found nothing out of the ordinary.

So I did not want to buy a blower motor resistor since I heard that if it WERE the resistor I would have had full blower in position 4 but I do not.
Any suggestions? Sorry for long post but wanted the info out there.

Tomorrow I guess i will buy a blower resistor and see if that solves the problem but I am doubtful it will. If it solves it I will post back here.
Any suggestions welcome.

wormdunker

Did all speeds work before you replaced radio? If you removed radio make sure you didn't unplug the vacuum switch. I did that with mine trying to fix high speed blower only.

madmanmarty

Check all your wires & your connections first.
Since u did the radio, I would check the speed switch wires & swap the fuse.

ehall

You probably bumped the wire connector for the fan speed dial

malvarez10

All speeds worked last time I tried them (maybe months ago). I do not know where the vacuum switch is located. Ill look wormdunker.
I checked all my connections behind the blower switch and plugged in everything tight.
I will try to unplug the speed switch wire and see if that helps. Also what fuse would I be looking for. The users manual does not have anything listed for "blower motor" would it be the number 25 fuse labeled ABS, climate control, Cooling fan, brake switch"?
Either way I pulled EVERY fuse in the floorboard and inspected and saw no blown fuses. I will swap anyway.

wormdunker

The vac switch is right under the radio. Look at the slides handles and you will see the wire harness plugs in to it. I just bumped mine and that was enough to knocked it where it lost all power to fan.

CCKen

The blower relay may be faulty. Pic below shows it.


Roll the glove box down by removing the two rubber stops and the glove box will hang down.


You can try a new relay. Make sure it's a 12 VDC, 40 Amp relay.

CCKen

The HVAC Blower relay control coil is fuse F25 (15Amp) in the Junction Block (JB), and the HVAC Blower relay power contacts is fuse F6 in the Power Distribution Center (PDC).


See diagrams below.


JB:





PDC:

CCKen

Here's a schematic of your HVAC Blower circuit.

malvarez10

Thank you all so much for helping! I got it figured out I highlighted the problem and solution in bold so you dont have to ready the troubleshooting steps it took to get there. The schematic was a HUGE help.

I was able to trace every wire and deduce that even with the resistor assembly REMOVED you should still be able to get the blower to work on setting 4 which mine did not. I traced every speed setting (which is just sends ground to the resistor assembly and grounds the fan at different resistances; 0, .2, .9 and 2.2 ohms) and found that the resistor assembly was good, so that means my grounding side was good.

So the problem is somewhere on the 12v+ side of things. I had 12v from the fuse box to the relay, the relay got 12v from the ignition and I could hear it click on and off with the key (I also tested the relay on the bench to make sure it made closure, it did) and sent that 12v to the fan. So what was the problem? For whatever reason the original 12v that came out of the fuse box would give 12v but was completely unable to power ANYTHING. I have never seen something like this before, it had 12v but couldn't even power a tiny little pc fan, or even a tiny 12v LED light. I also tried replacing the fuse. Still had 12v but could not take any load.

So I ran a new 12ga wire from the battery fused at 20 amps and spliced it into the factory red/light green wire on the relay plug so I had a "fresh" 12v that would be delivered to the fan. Works perfectly now. And since I replaced the 12v before it got switched by the relay the ignition turns the fan on like nothing is changed.

Sorry this was so long winded Im sure most of you dont care about the steps I took but it might help someone some day who stumbles onto this. I can say Im an almost expert now on the fan wiring and how it all works. Now to find out WHY this happened...or what else could have lost power...

CCKen

Might be corrosion in connectors C209 or C201.


Sometimes connector C201 can be troublesome because it is held together with a bolt that loosens up. C209 is next to the blower relay but rarely screws up.

caged

when mine (99) quit working intermittently, i just messed with the wire (pushing/pulling/manipulating) the wire under the hood that connects the power to the blower motor. since then, it hasn't happened in probably a year or more now.
so who knows, it might work for you too.