Issue: When the setting for the fan (off-1-2-3-4) is set to 3 or 4, the fan will most likely stop blowing at all settings. Turning the fan off for some amount of time will "correct" the issue and allow settings 1 and 2 to be used. On settings 1 and 2 the fan does not cut out.

It is possibly important to note that when the fan will not turn the AC compressor does engage and operate.

From scouring the net, I'm led to believe that this is due to a faulty resistor module.

So... I replaced the resistor module this morning -- no change in result. After some load for a while, and usually only when switching fan speeds, the fan stops working.

I swapped back to the old module, didn't mount it (just dangled it from the wires), thinking it may be a loose connection or some type of wiring issue. I reached down to make sure there was a firm connection -- and proceeded (dumb me) to grab the module firmly and burned a finger on the back of the module (the large white resistor) as it was -very- hot to the touch.

a) should the module be getting very hot? ie, is this normal?

b) what else could be the issue here?

 

that resistor does get red hot. the white material your refering to is ceramic, it can withstand the heat. normal. sounds like you have a faulty fan motor switch or a wiring issue between the switch and the motor. most of the time the resistor does fix issues like this.

 

Can't offer much additional about the cause of your problem - (but if it was the same with the new pack then the only other choices are switch and wiring)

But I can offer something re: the hot resistor pack. They do indeed get very hot - and that's precisely why these things are mounted inside the fan housing - so the air flow can keep them from burning out and/or melting something nearby. So hanging it below the fan was not the best set up even though I understand your testing logic.

Ron

 

After further thought and looking at the wiring diagram, I'm more inclined to believe it is a switch or wiring problem.

The resistor pack has three resistors wired in series. On position 4, voltage is applied directly to the fan motor (no resistors in the circuit) On position 3, one of the resistors is in the circuit. At position 2, there are 2 resistors in line in the circuit and at position 1, all three resistors are in line and in the circuit.

So when you say that in "failure mode", positions 1 and 2 still work, then current has to be flowing through all of the resistors - thus none are blown out.

The fan switch not only selects which resistor gets voltage, it also activates the heater blower relay so it's possible that your switch is losing contact with the relay on positions 3 and 4.

PM me and I'll try to send you the circuit diagram. WIth a 12V test lamp you should be able to trouble shoot the problem.

Ron

 

its a failed resistor.

replace it.

 

Not so fast, manybrews,

a) Changing the module was the first thing deusued tired. What are the odds that the new one had the exact same fault?

b) The blower wont run on switch position 4 - High Speed. This position does not even connect through the resistor pack (thus the high speed) No way a resistor problem could cause 4 not to work.

c) Postions 1 and 2 do work. As noted above, position 1 connects through all three resistors. If the fan runs on 1 then all resistors are good.

d) Finally, deusued was correct in thinking that the lack of A/C might be important. There is no connection whatsoever between the A/C control unit and the resistor pack. HOWEVER, the A/C Control Unit just happens to get it's power feed directly from terminal 1 of the.....(are you ready?)......Blower Speed Switch, by way of the Blower Motor Relay.

I believe one of these (most likely the switch since deusued says the problem often starts when switching speeds) is the culprit.

Ron

 

Ron,

Thanks for the responses.

I've been out of town since I posted this and will start my search for a switch shortly - looks like a dealership might be my only recourse.

An additional note: if the truck is started with the blower on setting 3, it will work for about 5 minutes; if the truck is started with the blower on setting 4, it will work for about 3 minutes. once "failed", the switch needs to be set off for about 5-10 minutes, then can be restarted. settings 1 and 2 never have this failure, as mentioned above. after the truck has been running 1 or 2 for a while and we switch it to 3 or 4, it fails --again as mentioned above.

I add this note b/c I spent some time driving around right before I left to try to qualify all of the means that the failure condition occurs.

Does the above change your recommendation at all?

- Will

 

Thanks Will:

Good info. The higher the setting, the greater the current flow. If the switch contacts or wiper arm are pitted and not making good contact, then since more current = more heat, at some point something loses contact and stays that way until it cools down. For this to happen sooner on 3 than on 4(and not at all on 1 and 2) would seem to make sense.

Here's a place you can call to check pricing on a switch (or maybe the whole panel if cheap enough) http://www.msrecycling.com/

Let me know if you want a copy of the wiring diagram. It would be fairly easy to confirm that it's the switch using a test light or continuity tester.

Ron

 

Hi Will:

FYI, I recently bought some used parts from this guy. Prices are very reasonable.

http://springfield.craigslist.org/pts/1212073807.html

Also, there's a '99 Montero parts car at a yard here in the San Francisco area. The've been a bit pricey in the past but let me know if you want the #

Ron

 

Blower Speeds at 1, 2, 3, not working. I read on this forum of others who replaced their blower speed resistor to fix the problem. So I get a new resistor and replace. I works for less than a day and now I have the same problem. I guess the resistor failed again. What would cause that resistor to fail? Is it upstream electrically from the resistor? Starting to get warm in Kansas and could really use some AC. Hope someone can point me in right direction.