4x4Wire TrailTalk

A/C fan not working

Posted By: hvw

A/C fan not working - 07/11/07 01:01 AM

My interior blower will work on 3 speeds for about thirty seconds and then drop down to the lowest speed. When it is working and I put in high(the fourth speed) it drops down to low immediately. I replaced the blower motor and fan which had frozen up with a new one from Toyota. I also replaced the heater relay. I'm wondering if the switch itself isn't bad. I looked at it but it would be a booger to get out. Any thoughts appreciated. It's hottern you know what around here. This is a 93 4x4 truck by the way. Thanks
Posted By: kewlynx

Re: A/C fan not working - 07/11/07 02:06 AM

Replacing the switch isn't too bad, but more likely the blower resistor is bad. If like the earlier trucks, it sits up behind the blower motor and is held in place by a phillips screw, with a plug and about 3-4 wires going to it. Looks like a bunch of little coils.

Dealer or junkyard part.
Posted By: cam01

Re: A/C fan not working - 07/11/07 07:34 AM

Quote
Replacing the switch isn't too bad, but more likely the blower resistor is bad. If like the earlier trucks, it sits up behind the blower motor and is held in place by a phillips screw, with a plug and about 3-4 wires going to it. Looks like a bunch of little coils.

Dealer or junkyard part.

Usually only works on high speed when the resistor packs it in as the high fan speed is direct power without any resistance.
Posted By: fourwd1

Re: A/C fan not working - 07/11/07 04:33 PM

Quote
Quote
Replacing the switch isn't too bad, but more likely the blower resistor is bad. If like the earlier trucks, it sits up behind the blower motor and is held in place by a phillips screw, with a plug and about 3-4 wires going to it. Looks like a bunch of little coils.

Dealer or junkyard part.

Usually only works on high speed when the resistor packs it in as the high fan speed is direct power without any resistance.


Correct, when one of the resistors opens up you will loose one of the lower speeds, but you'll always have the highest speed.
It would still be wise to pull the resis module and check it, but it doesn't sound like the culprit in this case.
Posted By: hvw

Re: A/C fan not working - 07/11/07 11:44 PM

Thanks folks. I checked the continuity on the resistor and it appears to be good. That is it has continuity at all terminals all the time. I did the check by touching the various terminals with a meter. If that's wrong someone let me know.

I'm certain that the blower motor will run at the highest speed if wired directly to the battery. The blower is new OEM. I haven't checked it yet but will in the morning. Everything worked correctly for awhile. I replaced the old one because it had frozen up.

Right now I'm suspicious of the fan switch. It just seems like a pain in the butt to get out.

The fan will only blow at a low speed at the high setting of the switch. At the next level down on the switch it will blow correctly for a few seconds then drop to low speed. It works correctly all the time at the lowest setting. The AC is ice cold. Just won't blow right.

I appreciate all your thoughts on this problem. It's obvious I'm kinda out of my area on this.
Posted By: 4Crawler

Re: A/C fan not working - 07/12/07 12:33 AM

One test to try is put a volt meter across the motor wires (as close to the motor as possible). Then see if the voltage drops when the speed drops. If so, that is telling you something upstream is limiting the current (and voltage) to the motor. If not, it is something inside the motor that is messing up. On mine, it was worn brushes in the motor causing it to overheat and slow down after running for a while:
- http://www.4crawler.com/4x4/CheapTricks/Blower.shtml#MotorRepair
Posted By: hvw

Re: A/C fan not working - 07/12/07 10:43 AM

That's a good idea and one I hadn't thought of. While fiddling around last night I noticed that if I jiggled the switch lever the blower would come on and off in the lower positions. Nothing on the high setting still. I believe using your suggestion I'll see a voltage fluctuation when I jiggle the switch. It seems to be my lot in life that the problem part is invariably the the one that is hardest to get to. That would be the switch.
Posted By: hvw

Re: A/C fan not working - 07/12/07 03:38 PM

May have found the problem. I pulled the blower switch and found that it had overheated to the point that parts of it were melted. One of the contacts had melted into the housing and was making no contact at all. I don't know if this was caused by the resister or not but I'm going to go ahead and replace them both. I didn't find any evidence of a short and nothing else seems wrong.

With any luck that will cure the problem. It may be that when the old blower seized up it caused the switch to overeheat if it was left on. Thanks to all for all the advice on this weird problem.
© 2021 4x4Wire TrailTalk