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Old 09-07-2011, 08:14 PM   #1
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Fan decides it's low-speed only

My fan speed was set to the highest setting when I decided to turn my dial to the A/C position, on account of IT'S SO DAMN HOT!, and when I went back to turn the fan speed down a notch, the fan sounded like it had a momentary clunk, followed by a lotta nothing. Curiously, the fan WOULD work at it's lowest setting, but it's a long wait to cool off a boiling cabin. 8^)

The upper three speed settings made the fan go off (presumably with the compressor still engaged). I took the dash apart and saw no obvious shorts, so I'm assuming the problem's with the switch. Could it be a relay closer to the fan unit instead? Any surefire obvious answer everybody here's seen before?

Thanks in advance.…

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Old 09-07-2011, 08:16 PM   #2
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Resistor behind the knob sounds like it is the culprit. It's an 8 dollar part... Easy to do

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Old 09-07-2011, 09:03 PM   #3
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Does sound like the resistor. Not sure exactly where it is on the TJ but they're always in the side of the heater box. Either in the passenger footwell or a little higher behind the glovebox. Should be a little plastic plate with a couple of screws and a 4 pin connector. Quick and easy fix.
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Old 09-10-2011, 07:21 PM   #4
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There's a resistor behind the knob? The switch itself?

Check my logic:

I was on fact only getting a blower at low speed on the lowest speed setting, even at rest, so I jumped straight to testing the switch. At the lowest setting, I was getting continuity on the A and B tabs ( green and tan wires, respectively). I got no continuity at all on any other combination of tabs on any of the other speed settings, so my conclusion is a faulty switch. A bad relay or resistor wouldn't give me a low-only result, right?

I couldn't find anything that looked like the relay in the service manual, even after taking out the glovebox.

Switch then, right?

Jon
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Old 09-10-2011, 07:26 PM   #5
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Even when off it was running at low speed? Sounds like either bad switch or relay.... I'm a commercial control/ hvacr tech lol so jeep wiring isn't my forte but Def sounds like a relay/switch if running when set to off
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Old 09-10-2011, 07:29 PM   #6
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It could be a relay if contacts are welded shut aka stuck in the closed position
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Old 09-15-2011, 11:42 PM   #7
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^ This would be true except 99.9% of failed relays I've seen are stuck open. Furthermore if it was stuck closed feeding constant voltage to the blower motor, the switch would still be able to change the speeds. I'm out of town and don't have any wiring diagrams handy but by what you're describing, maybe a bad switch is possible, but I'm almost certain you have a bad resistor. It's not behind the knob, it's on the airbox itself, it should be somewhere up in the passenger footwell (see my previous post)
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Old 10-07-2011, 05:59 PM   #8
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OK, the switch is replaced and TA DA!, nothing. In fact, I think I previously mistook another electronic sound for my blower at low speed, because it's blowin' nuthin. Checked the fusebox again -- still OK. With no speeds runnin', does this make the resistor block the culprit, or something else? There doesn't appear to be any fried wiring or connections.
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Old 10-08-2011, 07:41 PM   #9
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Well if it's no speeds working, you probably have a bad blower motor. I have diagrams here for up to '95, so wiring colors might not be the same. But look for a 2 pin connector by the blower motor. If colors are the same as in '95 (hit or miss) it would be a 14gauge black/tan stripe wire for positive and black for ground. Either way, find the connector, you know what you need, power and ground. Pull the connector, probe the terminals... with the blower switch on, if you have voltage and ground, you have a bad motor (assuming the connector is good). Often when a motor goes bad it will blow the fuse, did you originally find any bad fuses?

I'm thinking the resistor is not the problem now that I have a diagram in front of me. Again it's for a '95 but the overall setup should be the same, and only low and medium speeds go through the resistor. High speed gets full 12V directly from the switch. With a bad resistor you would be able to run it on high.
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Old 10-24-2011, 06:06 PM   #10
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Just had the same issue, it was not the switch itself for the fan (behind the knob). It was the resistory that is attached to the blower fan itself, behind the glove box. Its held in by 2 screws and is a 25 dollar part. Its not too bad to replace, took about 30 mins, however if you have big hands it may be tricky. Also removing the little courtesy light under the glove box makes it easier to get to.
I now have all 4 speeds again, wahooo
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Old 11-20-2011, 04:10 PM   #11
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I'm thinkin' gremlins have infiltrated my Jeep, cuz I managed to run my blower connected directly to my battery (and managed to ding my fender when I dropped my battery on it). So what do I have left to test? Don't know if the relay's dead, but it looks clean on the prongs. I hate to think I have to start tracing wires, a real pain in the ass. A bad resistor would still give me one speed.

Definitely frustrating, and I'm freezin' my butt off....

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