PETDOC

88 4Runner with 379,000 miles. I have owned and maintained this vehicle since new and several years ago had replaced the blower motor and resistor. Recently I've experienced a strange problem. My blower motor will work fine and then stop working at all speeds except for for low. When it stops working there is a moderately high pitched hum. If I turn it off and wait 30 minutes to an hour it will usually work for an hour to several days. I am waiting for it to totally fail so I can locate the source of my problem, but would appreciate any insights from others.

shadowbirdie

If you bang on it does it start running until the next time you shut it off?
379K most likely a worn out commutator in the motor caused by running the fan after the brushes have worn down to nothing and the brushholder and spring are now eating the copper commutator inside. Find a match at the boneyard, should be lots of them around the way people drive, unlikely you'll ever see the problem again in your lifetime as long as it works good when you buy it.. Not Repairable...most Toyota use the same fan assembly. 3 screws and plug in connector all there is to it

PETDOC

If that is the case, why does it work on low speed? I was trying to make it a resistor issue, but when they fail it is usually all speeds but high (i.e., no resistance) that stop functioning.

GePa

Hello, I had the same issue, in the end the part to blame was this little relay. I started like yours and then it stopped working at all, the relay was busted in the inside all loose




http://s196.photobucket.com/user/wil...g.jpg.html?o=1

PETDOC

That would make sense regarding my intermittent problem. I was waiting for the blower to stop functioning permenantly so I could localize the fault, but it has been working without interruption for about a week now. Still confused as to why when it stops working the low speed is still functional.

PETDOC

Shortly after last post the blower motor worked fine for a couple of weeks; however, yesterday I got my wish, the blower quite and has not revived. If I turn the switch on anything but low there is a steady high pitched sound and no air.
Today I removed glove box and hooked the blower motor up directly to the battery-works fine. I then put the probes of a voltmeter into the wire coming to the motor. I got 11.8v on the 3 higher settings, but both off and the lowest setting registered 0.08v. Obviously the lowest setting isn't working and I suspect that may be related to a switch issue. Whenever the switch is on any of the 3 highest settings there is the high pitched sound. It is coming from the relay. If you feel the relay is has a mild vibration. Ordered a new relay at local Toyota dealer($17); will be in tomorrow. Assuming the new relay fixes the problem I don't understand the voltage readings I'm getting at the plug going to the blower motor. I would have thought with a faulty relay the voltage would be much lower.
To be continued.........

PETDOC

Disaster! New relay changed nothing.
Spoke with sage Toyota mechanic and he insisted despite me successfully running motor directly off the battery that it was the blower motor. New blower motor changed nothing!
It has to be the dash switch for the blower motor. Initially I got no voltage at Off and lowest setting, but 11.8v at 3 higher settings. Now I get voltage only at highest setting, all others read zero.
Will start new thread on approach to the dash switch.

PETDOC

Problem solved, I think. Before attempting to access dash control switch I pulled the resistor and it is fried. I never considered it as the problem because of how the blower motor failed. I replaced the resistor years ago due to a textbook failure, i.e., non-functional blower motor in 3 lowest settings and fully functional on the highest setting. In hindsight my voltmeter was telling me to look at the resistor and I failed to interpret results. The voltmeter showed 0 volts at OFF and in the lowest switch setting, and 11.9 volts in the 3 higher switch settings. I believe there should be a stepwise increase in voltage from the lowest to highest control settings. Based on the voltage readings it appears the resistor shorted across the higher control settings. What I still don't understand is why the blower motor didn't work on the 3 highest settings because per the voltmeter 11.9v was flowing to the motor. Perhaps there is more to this story, but for certain the resistor is blown.

PETDOC

New OEM toyota resistor and fan works at very low speed. Voltage at OFF and lowest settings are 0, next 3 settings are 12v. Fan runs at only one low speed in 3 highest settings. Obviously I've got another issue besides resistor.

PETDOC

ANY THOUGHTS ARE GREATLY APPRECIATED!
PROBLEM: blower motor only works at one very slow speed if control lever is set on 2,3 or 4. OFF and lowest setting the blower motor is off.
REPAIRS: 1) New blower motor, no effect.
2) New relay, no effect.
3) New resistor, allowed motor to work as stated.
4) New 10 and 20 amp fuses in heater/ AC slots, no effect
POSSIBLE CLUE: measured voltage at OFF and level 1 is zero
Measured voltage at level 2, 3 and 4 is 12.

grumpin

Switch or new resistor is bad or wrong resistance. Or a bad ground. According to the 88 wiring diagram the ground goes to the left front fender.

RJR

How did you apply 12V directly to the blower motor when you said it worked fine? There's some difference in the circuit between how you did that and how it's installed, since you indicate you measure 11.8V on it and it doesn't work when it's installed. I too would suspect the motor ground. A bad ground would give you 12V on the hot side of the motor but nowhere for the current to flow on the other side. Measure from the case of the motor to a solid frame ground when you turn on the blower switch to high. If you measure anything above .5 volts or so your ground is bad.

PETDOC

Ron,
I unplugged the 2 wires to the blower motor and inserted the 2 multimeter probes into the end of the wiring harness. I turned on the ignition and measured voltage at control switch settings of OFF, 1, 2, 3 and 4. Using alligator clips, I hooked the blower motor up to a 12v motorcycle battery and it runs great, full steam.
If it is a bad ground why would I be getting voltage at any control switch setting?
Curious why you don't believe it is control switch? The only issue regarding a possible control switch that I can't mentally resolve is why the blower motor, which on the 3 higher control settings is getting 11.94v, isn't running full steam.

RJR

OK, that's helpful. My guess is you have a high resistance connection somewhere, probably at the switch (or it's the switch itself). When you measure the voltage with your voltmeter, which takes no current, you get roughly 12V. As soon as you load the wiring with the motor, it can't deliver the necessary current and the motor doesn't turn. If you could measure the voltage at the terminals while the wires were connected to the motor, you'd likely measure a very low value.

Probably time to tear the dash apart.

PETDOC

And the rest of the story.... Inside the connector of the dash control switch to the main wiring harness there was a short. Removed the connector and spliced all the wires together. Everything now functions normally.
Just to satisfy curiosity, after the repair I unplugged the 2 wire connection going directly to the blower motor and checked the voltage for the various fan speeds. Now I get: OFF-0 volts, and 12.23 to 12.3 volts for switch levels 1, 2, 3 and 4. Electrical issues are not my strong suit, perhaps someone could explain to me why the voltage doesn't progressively increase from level 1 through 4, i.e., what makes the blower motor spin faster as the switch levels are increased if the voltage remains unchanged?

grumpin

Good job and thanks for the follow up.

Terrys87

iTrader: (1)

Do appreciate the follow up. I am weak on electrical but in my opinion and looking at the resistor, some how I think the resistance is changed when selecting the different speeds when going thru the resistor. You can see the different pathes of it.

From my very limited knowledge of electrical, the voltge would/should be the same? it is due to the resistance of the resistor there by changing the flow of current which would change speed???

Maybe some one could explain it better.

scope103

Your fan pulls, oh, 4 amps on high. That means it's effectively 3 ohms. To make it run half speed, you want it to get about half the current (actually, quite a bit more, but stay with me). So a series resistor of 3 ohms would do it: total of 6 ohms in the circuit across 12v gives 2 amps. 2 amps through a 3 ohm series resistor drops 6 volts, leaving the 6 volts for the motor.

When you disconnect the blower motor and measure the voltage right at the connector, your $7 HF multimeter is pulling about 10 micro amps (that's right; 10 millionths of one ampere). So the voltage drop is .00001 * 2, around 20 millionths of a volt. Which I can barely measure even with my fancy 6-digit lab voltmeter.

Now, if you measured the voltage at the blower connector while the fan was plugged in (say, by back-probing the connector), the fan would pull the current to cause the voltage drop you want to see. (My guess is that you'd see something like 6v on low; DC motors don't like low voltages, and 6v should be plenty slow).

You'll note that the FSM doesn't give a resistance spec for the blower resistor. If I'm right about my side-of-the-barn guesses, the resistances would be something like 0.5, 1, and 1.5 ohms. Again, to measure resistances that low you'd need my 6-digit lab voltmeter, and even then I'd have to get a "Kelvin probe." So there's no point specifying the resistance; it just looks like a short to someone using a reasonable multimeter.

RJR

Good explanation, scope. As scope says, sometimes just measuring open circuit voltage (which is what you're measuring when you disconnect the motor and measure at the connector) doesn't tell you the whole story. You really need to know the voltage while the motor is loading the circuit to figure out what is going on. That usually requires back-probing the connector in place.