Virginia Posted December 19, 2018 Share Posted December 19, 2018 More on this sage. I took the fan out and reconnected it to the battery. Ran fine. put it back in and turned the truck on but still no blower. So, either the resistor or the switch? Link to comment Share on other sites More sharing options...
Eagle Posted December 19, 2018 Share Posted December 19, 2018 Does the fan run if the control is set to the highest speed position? That position bypasses the resistors. If the fan runs on high speed, the problem is the resistor. If it doesn't run on high speed, the problem is somewhere else. I've never had to troubleshoot the control switch, so I can't help with that. Link to comment Share on other sites More sharing options...
Virginia Posted December 19, 2018 Share Posted December 19, 2018 37 minutes ago, Eagle said: Does the fan run if the control is set to the highest speed position? That position bypasses the resistors. If the fan runs on high speed, the problem is the resistor. If it doesn't run on high speed, the problem is somewhere else. I've never had to troubleshoot the control switch, so I can't help with that. No, it does not. The last time I had this problem, I first replaced the fan and that didn't work then replaced the resistor and it worked for about 2 years then stopped again recently. I don't know why a resistor would go bad so quickly nor do I know how to test to see if the resistor is good. Does one Ohm that? If it's the switch, would that mean tearing out my dashboard to get behind there and look? I'm not even sure what I'd be looking for? Link to comment Share on other sites More sharing options...
gogmorgo Posted December 19, 2018 Share Posted December 19, 2018 I've usually been able to visibly tell a resistor pack is bad. It's a bunch of coils of high-resistance wire which turn electricity into heat. Generally they've burnt themselves out like a lightbulb filament. You can ohm out the coils to confirm if you want, but you'll be looking at whether they'll carry current or not. If your fan is good, and the resistor pack is good, I would start looking at the switch next. As contacts in the switches go bad they'll start heating up and eventually start melting down the switch and burning connectors. There's also a not-unreasonable chance of similar issues elsewhere in the wiring, although I'm pretty sure there's a bunch of stuff that runs off the circuit for the blower motor, like the radio and wipers, so if those are working it eliminates a good chunk of tracing where the power stops. I'd start with looking for power at the resistor pack cause it's easiest, and then the switch. Link to comment Share on other sites More sharing options...
Virginia Posted December 19, 2018 Share Posted December 19, 2018 1 hour ago, gogmorgo said: I've usually been able to visibly tell a resistor pack is bad. It's a bunch of coils of high-resistance wire which turn electricity into heat. Generally they've burnt themselves out like a lightbulb filament. You can ohm out the coils to confirm if you want, but you'll be looking at whether they'll carry current or not. If your fan is good, and the resistor pack is good, I would start looking at the switch next. As contacts in the switches go bad they'll start heating up and eventually start melting down the switch and burning connectors. There's also a not-unreasonable chance of similar issues elsewhere in the wiring, although I'm pretty sure there's a bunch of stuff that runs off the circuit for the blower motor, like the radio and wipers, so if those are working it eliminates a good chunk of tracing where the power stops. I'd start with looking for power at the resistor pack cause it's easiest, and then the switch. Thanks Link to comment Share on other sites More sharing options...
Eagle Posted December 19, 2018 Share Posted December 19, 2018 The resistor pack also has a thermal fuse in it. I've replaced multiples of them, all because the thermal fuse blew. In my case, the problem was always mice building a nest in the air box. The nest material gets wadded and packed around the resistors and fuse, causing the fuse to overheat and do what fuses are supposed to do. One of these days I'll try my hand at soldering in a replacement fuse. Link to comment Share on other sites More sharing options...
Virginia Posted December 19, 2018 Share Posted December 19, 2018 35 minutes ago, Eagle said: The resistor pack also has a thermal fuse in it. I've replaced multiples of them, all because the thermal fuse blew. In my case, the problem was always mice building a nest in the air box. The nest material gets wadded and packed around the resistors and fuse, causing the fuse to overheat and do what fuses are supposed to do. One of these days I'll try my hand at soldering in a replacement fuse. I'll pull it and check it. Link to comment Share on other sites More sharing options...
Virginia Posted April 9, 2019 Share Posted April 9, 2019 I'm ready to pull my hair out about this. Now, I can be driving down the road and the fan will come on then after a short while it will just turn off again. It's intermittent now. Tells me it's a connection. I've checked grounds and they're all good. the connection to the fan motor is good because I can hook that directly to the battery and the fan runs great. Could the resistor cause an intermittent problem? Poltergeist? Link to comment Share on other sites More sharing options...
Pete M Posted April 9, 2019 Share Posted April 9, 2019 is it the original resistor pack? Link to comment Share on other sites More sharing options...
Virginia Posted April 9, 2019 Share Posted April 9, 2019 5 hours ago, Pete M said: is it the original resistor pack? Nope. I replaced it about 2 years ago. Link to comment Share on other sites More sharing options...
Pete M Posted April 9, 2019 Share Posted April 9, 2019 I would check every connection along the way including the resistor pack for corrosion. did you clean the grounds? Link to comment Share on other sites More sharing options...
Ωhm Posted April 9, 2019 Share Posted April 9, 2019 So the blower motor come ON, even with the Heater Mode Selector Switch is in the OFF position and your driving down the road? Link to comment Share on other sites More sharing options...
Virginia Posted April 10, 2019 Share Posted April 10, 2019 11 hours ago, Pete M said: I would check every connection along the way including the resistor pack for corrosion. did you clean the grounds? I'll check the grounds again. The resistor could be corroded because it's right in the area of the leak I was having in the passenger footwell. I think I have that fixed. Link to comment Share on other sites More sharing options...
Virginia Posted April 10, 2019 Share Posted April 10, 2019 10 hours ago, Ωhm said: So the blower motor come ON, even with the Heater Mode Selector Switch is in the OFF position and your driving down the road? Sorry...no. I have the switch on all the time. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 10, 2019 Share Posted April 10, 2019 Wiggle the blower motor connector and see if the fan comes on. Doing that lead me to this fix: On 87 to 90 MJs and XJs, the blower motor’s factory grounding point is on the driver side inner fender under the sheet metal screw. This ground is shared with windshield wipers, front windshield washers, rear windshield washers, AC clutch relay, fan control relay, fog lamps, fan motor, headlamps, front turn signals, front side markers, and park lamps. So your blower motor has its ground point 10 feet away from where it is located!! What we’re going to do is leave that ground intact and also ground the blower motor on the passenger side inner fender much closer to the blower motor itself. This will also benefit the other components on the factory ground circuit. Take this opportunity to refresh the factory ground as a matter of course. Remove the screw, scrape the surface to bare metal and reinstall the screw securely. Here’s what I do to get the ground much closer to the blower motor and add another ground point to this overloaded ground circuit. Find the blower motor connector on the passenger side. Red and Black two wire connector. Find a location where the black wire can be made to reach the passenger side inner fender, and cut the wire. You may have to do some rerouting of the harness to achieve this. Take both cut pieces of wire and put them together into a yellow eyelet and crimp. Fasten the eyelet to a place on the passenger side inner fender with a sheet metal screw after applying OxGard to the contact surfaces. Be sure to scrape the attaching point on the fender to bare metal first. Your blower motor will now turn faster and last longer, and the other electrical components on the circuit will benefit from a better ground path. Link to comment Share on other sites More sharing options...
Virginia Posted June 16, 2019 Share Posted June 16, 2019 On 12/19/2018 at 6:16 AM, Virginia said: More on this sage. I took the fan out and reconnected it to the battery. Ran fine. put it back in and turned the truck on but still no blower. So, either the resistor or the switch? So, I put a new resistor in and that didn't fix it. Still no blower. I can hear all the things opening and closing behind the dash but no blower. Could the plug on the wiring harness be bad? Oops... Just remembered that I needed to check the ground and make the connection closer thought it's worked in the past without moving the ground. How do I test the plug? How hard is it to take off the dash to see the switch? Link to comment Share on other sites More sharing options...
Eagle Posted June 16, 2019 Share Posted June 16, 2019 The resistor only controls the lower speeds. If the resistor pack is blown, the fan should operate with the switch in the high speed position. Link to comment Share on other sites More sharing options...
Virginia Posted June 17, 2019 Share Posted June 17, 2019 The blower doesn't work at any speed. Link to comment Share on other sites More sharing options...
Pete M Posted June 17, 2019 Share Posted June 17, 2019 there is a downloadable pdf of the factory electrical manual in the link in my sig. do you own a multimeter or test light? Link to comment Share on other sites More sharing options...
Virginia Posted June 18, 2019 Share Posted June 18, 2019 On 6/16/2019 at 5:39 PM, Eagle said: The resistor only controls the lower speeds. If the resistor pack is blown, the fan should operate with the switch in the high speed position. 6 hours ago, Pete M said: there is a downloadable pdf of the factory electrical manual in the link in my sig. do you own a multimeter or test light? I own both. Link to comment Share on other sites More sharing options...
Pete M Posted June 18, 2019 Share Posted June 18, 2019 that should be able to point you to where power should be. I believe the plug for it is in the engine bay and should be easy to get at. use the meter to check for both power and ground. you can also check for power at the resistor pack. Link to comment Share on other sites More sharing options...
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