JEBSR5

90 4Runner SR5
4WD 3VZE V6
AC/Heater problem.
I have a continuing problem with my blower switch (4 speed, I think), it keeps melting the switch when using highest setting. I no longer have a high and next lower speed, unless I push downward toward floor and then it works on last highest speeds. This is my second switch, used ones. New ones are very expensive. First 2 speeds work with no problem. I don't think there is anything wrong with the blower fan motor since it still works. It just builds too much resistance on high and melts switch on two highest speeds.
I know there is a reostat and blower resister in wiring diagram. Not sure what either does, but could the blower resister be the problem? Anyone had this problem? I don't want to throw money at it, little of that. I definitly have to get a switch, but that will melt too, unless I can figure this out. Any suggestions welcome.

Flamedx4

I took a look at the diagram and the control circuit is pretty standard stuff. So....
Since the blower seems to operate properly (you did not actually say the speeds seem to be working correctly with the switch, but I'll assume so,) the resistor and the relay 'appear' to be working. Note that on High speed those are bypassed. Sooo -
Unless the resistor can bleed off to ground and pull more current through the switch than it supposed to, I'd suspect the blower motor or the connectors.
The resistor is cheap, so you might consider replacing it anyway.

I would put an Ampmeter (not a Voltmeter, a DC ampmeter capable of reading as high as 30 amps) on the fuse or the motor hot lead, and check to see how much current the motor is pulling. First off, be sure the correct fuse is in there (30 amp) A blower motor will draw about 25amps at full power. So, if the motor is not drawing too much (bad blower) then look at the ground to the switch. A bad ground can increase the resistance and raise the amperage. Also check the connectors at the switch carefully, a loose fitting pin can again increase the resistance and generate heat. Check the connectors on the blower itself too. When looking at the connectors, look for any signs of heating, and examine the pins themselves closely. If you get all that done, you should have solved it. Good luck!
Here's the diagram-

JEBSR5

I agree, have the same diagram and noticed when on high, basically it bypasses resistor. I really don't think it's the ground since many things run off same ground and having no problems, of course none probably pull that much amps, but will check just the same. Last I checked, connector was fine when replacing first switch, may not be now that second switch suffered same fate. I'm sure fuse is correct, checked many times, never has blown, so I'm leaning toward motor like you. Now just have to remember how to measure resistance an scrounge up a meter.

Was looking at abbreviated version earlier, then got out detailed one. That's when I discovered no resistor involved in high.

So, just like you say, it has to be the ground or the motor. Power goes straight through motor from switch on high.

Thanks for the two heads better than one advise.

JEBSR5

Another note, yes all speeds seem fine if as noted above you push down on fan switch to get last two speeds. Also note my wiring diagram shows not a fuse, but a 40 amp CB, what ever CB stands for. The CB feeds the relay, then to the heater fan. The CB is on relay block 3, which is on the right upper kick panel. Still investigating and hunting a way to get a tool to measure amps.

Dryheat

Mine was doing the same thing. If you can check the current draw. I had to take the dash apart to get to the switch and cleaned the carbon off of the contacts. Now it works fine. Just be careful getting the switch case open and don't lose any of the pieces. Good luck.

Paul

JEBSR5

I've had it apart twice, this will be my third switch. Did you have to replace the motor on yours? I'm still looking for a meter big enough to measure the draw on it. Mine just goes to 10amps. I really don't think it's the motor, but like what you encountered. Either dirty contacts or a poor ground splice in wiring.

JEBSR5

Finally got blower fan switch out, fried. It's as I said in earlier post, high and next to high (med2) had really got hot enough to melt switch, etc. Got a really new looking switch in salvage yard, plug on existing switch and contacts look like they been hot, but not bad, the plastic plug they go in is bad shape. I cleaned up contacts and put some conductive grease on each plug and contact of switch. Contacts looked like they were really biting in to switch and not loose. Tomorrow i'm going to try Advance and Autozone to see if they can test the amps or power draw on fan motor. Still can't find resistor, but only low, med1 and med2 run off it. High runs straight through, although high and med2 are melted around plastic, I'm thinking it may be motor pulling too many amps. Testing will tell for sure i guess, hope i don't need motor, they are a little steep.

Anyone have any ideas where resistor is? I have whole bottom dash off and don't see it yet, thought it was near anti lock module, guess not.

Dublin

I've gone thru 5 switches myself, but not lately. I found out the blower motor tends to initially draw a lot more if the switch is left on high while starting. it seems the starter and the blower both try to draw as much as possible while cranking. By always turning the blower off before starting you can dramatically extend the life of your switch. During normal operation with the vehical running there is only a brief spike in amp draw, but while cranking over with the switch on high it pulls for a much longer duration. The lower speeds do not seem to effect amp draw nearly as much.

JEBSR5

I'm guilty of that once in awhile, but not very often. I couldn't find an ampmeter big enough to test, but once out found motor very stiff. Went to Advance and they couldn't test old motor for amperage, but ordered a new motor after looking at one for an 88 and seeing how easy it turned by hand. Naturally I figure, stiff to turn certainly means it's going to take more current to spin. I had one person there tell me that the resistor is supposed to stop that from happening. well, that's not what the resistor is for, it only controls speed. Long story short,

Thanks for reply.

taikowaza

Good to see that you have replaced your switches. Could you walk me through the replacement of this switch, including the removal of the dash?
it is a shame that the switch can't just be replaced without taking apart the whole 9 yards!
thanks, and pics would be great
best
T

Rory

One day I was driving home and started smelling the stink of electrical burn. Then I saw smoke billowing out of the climate control head and knew there was a problem. I assumed it was the switch but I wasn't sure, I was thinking the blower could be drawing too much as any electric motor demands more the older it gets. Either way I am glad you guys found this much out about it. Mine got so hot that the knob melted off of the lever and now it is permanently gummi, as in the plastic won't solidify.

So which is the most common cause then; dirty switch contacts? bad connections at the plug? blower current draw too high? or bad grounds?

My guess would be switch contacts because all kinds of dirt and crud seems to end up going inside the control head.

taikowaza

Got to replace my fan switch in the HVAC...
is there ANY way of doing this without taking the whole dash off?
I take off the drink holder, remove the fan knobs, (hi/M/L etc), pry that off, then I can see several screws, but the clock is in the way...

if there's any way to replace that ^*^$ fan switch which is less than a major ordeal I'd love to hear it! I got quoted $175 plus parts from the stealer.

^VooDoo^

The resistor should be to the right of the motor, Mine is bad and speed 3 is the same as 2, I had it out once to check it and it was toast.
lvl 3 would be nice but Ive gone without it so long, Dont care anymore.

ssgmullins

when i turn my speed control switch on it clicks in the relay on the passenger side. So i am assuming that the speed select switch is good but i have no air on any speed. i pulled the resistor out it looks fine. All fuses are good. is there anything else to check or should i try to change the resistor then the blower motor? Please help it is cold and i have no heat. 1994 toyota pickup

HappyAdventure

If the relay clicks when you wiggle the switch, it might be that the switch has gone bad. They tend to overheat, melt and then the contacts stop making contact. There is some info in the FSM on how to check the switch, relay, resistor and motor with a multimeter to figure out which is broken. This thread may also help.

ssgmullins

But since the relay is clicking when I turn it on I don't think it is the switch because it is sending power to the relay. U think it is still the switch

HappyAdventure

I can't really say from my end, but when my switch went bad it was acting as yours is. But the resistor packs go bad as well. The switch might be a good place to start, it is a bit of a pain to get to but relatively easy to see if it is working. I would start by checking the continuity between the different terminals on the switch with the switch in different positions(look on page AC-37 of the Factory Service Manual there is a sticky at the top of the 86-95 truck forum if you don't already have it). You could check the resistance through the resistor pack too, but I don't know what the resistance is supposed to be, but if it is way high or not conductive at all it is bad.

You might be able to find the parts at a pick n pull if there is one in your area that has more than just domestic cars.

chris_123

Most vehicles use a relay for High Speed. If you have the wiring diagram it is easy to install a 30 or 40 Amp relay near the blower motor itself so the relay and not the expensive and hard to replace switch does the heavy work. Basically the switch turns on the relay coil (about 1/10 of a Amp) and the relay contacts handle the motor current.

scope103

So anything other than "high" speed goes through the switch and resistor pack as before? Given that I hardly ever use "high" speed, this sounds like a bunch of wiring for not much improvement. (But maybe my lack of use of "high" is why my switch still works ...)

wyoming9

iTrader: (1)

I have had to replace resistors over the years but never a switch.

Loose connections will always cause heat.

For the most a very old thread