2000 TJ sputters while driving when cold

[greg92jeepxj]

X2 on the blower motor resistor. When they corrode , more resistance than the normal speed resistance causes excessive heat to the wiring between the switch and blower motor resistor causing electrical over draw as JPinPA posted . This is common . Yes , wiring will have to be replaced . Bummer.

 

[GAjeepGirl85]

I replaced the resistor when I replaced the fan. I checked the old one before I ordered the fan. It read out ok but was pretty heavily corroded. It was cheap so I figured I might as well change it out.

After further inspection, I found that the one small connector with 3 wires was melted along with the wires going to it. Once I removed it I could see the circuit card was burned up too. The terminals on the back of the blower speed switch are melted. The previous repair replaced the connector with spade terminals which weren't insulated very well. They may have been shorting together.

I was able to find the panel on rockauto. Just need the small 3 wire connector. Id like the 5 pin connector for the blower speed switch, but can get by with spade terminals if need be.

 

[GAjeepGirl85]

Found both connectors. That little 3 wire one was a ***** to find and its expensive. I should get the parts in a week or so. Ill let you know if anything else comes up.

 

[JPNinPA]

Good luck!

Post up any issues or questions.

 

[GAjeepGirl85]

After reading a bunch of posts it seems the weak point in the circuit is the connection points. That is where the excessive heat is coming from, causing things to melt. I am debating soldering the wires directly to the terminals on the backside of the switches. Seems like that would solve the problem.

 

[JPNinPA]

After reading a bunch of posts it seems the weak point in the circuit is the connection points. That is where the excessive heat is coming from, causing things to melt. I am debating soldering the wires directly to the terminals on the backside of the switches. Seems like that would solve the problem.

I wouldn't recommend soldering the wires. It improves nothing and likely melt your new switch or something else if another item is at fault or not operating optimally.

Well that(connection points as cause) is somewhat true.

Consider if everything is working properly except one contact is resistive. Then that contact will heat as current passes through it. Over time with a constant current the plastic may melt. If the connection becomes more resistive it creates more heat more heat faster melting. This can happen and is most likely when the fan setting is on high where the current is the highest.

Now consider all wires and contacts are good but the current becomes excessively high. The weaker or resistive points will get hot even though they are operating normally or typical resistance. . Wires and connectors may become toaster elements due to the higher current. Excessively high current can occurs if the motor is stalled (frozen not allowed to spin) or just being held back by dirt or bad bearings. You will likely notice the slower fan settings failing first leaving only high fan setting working. This is due todos the resistor bank is made. It is various lengths and widths of metal lines. The thinner and longer metal traces are higher resistance for slow speeds. Those are most likely to fail first in this scenario. As described above the higher resistor will heat to higher temperatures until it fuse open. Then that setting no longer works.

I would replace the components clean all connections and grounds add some thermal grease in the connections to keep them from oxidizing.

As a safeguard I'd add a slow blow fuse in line with the resistors and switches. Somewhere it is easy to replace. I'm not sure what rating yet but I'd rather replace a fuse than a switch, wiring and motor...

http://www.jeepforum.com/forum/f9/ac-heat-blower-switch-melting-608645/


http://www.fourwheeler.com/how-to/electrical/154-0710-jeep-fire-prevention/

 

[GAjeepGirl85]

I read the links, still don't understand how adding a relay will help? How is it going to limit the current?

 

[JPNinPA]

A relay uses low voltage low current to close a switch for a high voltage high current load side. By connecting the fan speed select switch to the relay low side and the blower motor to the high side the current does not go through the switch.

 

[GAjeepGirl85]

Oh!!!! Gotcha.....I guess I didn't understand how it was wired up. Now I get it.

 

[JPNinPA]

I replaced the resistor when I replaced the fan. I checked the old one before I ordered the fan. It read out ok but was pretty heavily corroded. It was cheap so I figured I might as well change it out. After further inspection, I found that the one small connector with 3 wires was melted along with the wires going to it. Once I removed it I could see the circuit card was burned up too. The terminals on the back of the blower speed switch are melted. The previous repair replaced the connector with spade terminals which weren't insulated very well. They may have been shorting together. I was able to find the panel on rockauto. Just need the small 3 wire connector. Id like the 5 pin connector for the blower speed switch, but can get by with spade terminals if need be.

Have you nailed down all the issues yet?

 

[GAjeepGirl85]

I got all the connectors and relays in on Thursday, but was out of town this weekend. Should be able to knock it all out tonight.....possibly tomorrow if need be.

 

[GAjeepGirl85]

I replaced the panel and the connectors. Wired in two 40 amp relays to bypass the two highest fan speeds. Pulled 12 volts from the radio, seemed to be the most convenient spot. Used the large black wire that goes to the 3 wire connector for the ground. Everything is working now. Drove around cycled through everything, all is good.