AC fan speed control

Does your climate control show the fan speed, and if so, does it show a low fan speed even though the fan is running on high? If that is the case, check the resistors by the blower cage. One or more may be bad.

"..... does it show a low fan speed even though the fan is running on high?..... "

Yes it does. The climate control shows the fan speed dropping down (fewer, shorter bars) but the fan still continues to run on high speed. Where can I find some detailed information about components and schematics? My Haynes manuel has the standard " Installation Is The Reverse Of Removal" directions, with no details at all.

Larry In the back yard, under the oak.

If the climate control shows the fan speed dropping but the fan continues to run on high, then I would check the blower resistors. The only place I am aware of with detailed information is the factory service manual, but diagnosis should not be too difficult with a volt/ohm meter. The resistor pack or frame is usually located in the air flow from the blower so that the air cools the resistors. The resistors turn the electricity into heat and the air from the blower gets rid of the heat. The reduced current going to the blower motor reduces the motor speed. If the resistors don't resist, then full power goes to the blower motor.

The blower motor is usually located under the passenger side of the dashboard, and removing the shroud around the blower should provide access to the resistor pack.

All of the resistors would have to be shorted out to have this effect. Somewhat unlikely. Resisters tend to go "open" (infinite resistance) rather than "short" (zero resistance). Don't forget, if resistors are used to slow the motor in the manner suggested, then they must be in series with it. Me, I'm not convinced that this is the actual design, and that the fault is a bit less obvious.

Jay I tend to agree with your observation about the design of the circuit, HOWEVER..... checking the resistor pack appears to be a rather easy approach. Of course, after I have spent a couple of hours standing on my head upside down in the passenger foot well, I may change my mind.

Another suggestion I have received is that the control head in the console has developed a problem. The switch has gone bad or relay is out. But I'm not sure how to get the trim off around the gear shift lever. Haynes manual not a big help. And none of the local parts houses have (or even know what I'm talking about) a nylon-type pry bar for the trim. I don't want to scrap that stuff trying to get it off. Any ideas on that? What do you use? And just where are the clips located? I don't want to be jacking it up at the corner when the clip is in the middle. Done that before in the old Mercedes and cracked the trim. Bummer.

And even if I do get it out, what am I looking at? Back to the problem of locating diagrams and flow charts. Yea, the resistor pack seems to be the easiest to check tonight.

Larry In the back yard, under the oak.

Larry, My manual shows 10 clips around the console. The instructions keep repeating to tape the end of a screwdriver to remove. Unfortunately, I didn't purchase the electric/electronics manual. Nick

Here are some instructions on removing the trim around the shifter:

Ray Thanks for the link. Looks like their phone holder works well. Loved their directions on the trim.

Larry In the back yard, under the oak.

Nick Does it specify gray duck tape or black duck tape?

Larry In the back yard, under the oak.

You're welcome! Good luck with the project!

If there's a full-speed fan relay to cut out all the resistors, then it could be stuck on. Not sure if your car uses this, but it is the typical wiring.

I agree -- if this is the design, it is the most logical fault point.

Update.... Thanks very, very much for the diagrams, whoever you are! They helped more than you know. The saga continues. On Thursday, the fan that had been running full blast, suddenly quit! Nothing! No air, no fan, Nothing! And it's about a hundred degrees at lunch time. Now the priority goes way up to get this fixed. Full speed AC fan in Florida in the summer time is not that big a disadvantage. But no AC at all!!?! Now that's a problem. Anyway, what I have found so far... the Blower Motor Control Relay gives a bad readout. Power In OK, Power Out OK, Ground In OK, Ground Out NG (No Good). By jumping the contacts, fan runs full speed again. So the fan motor is OK. The speed dial and the temperature dial still have no effect on the fan speed, but I think that may be due to the bad reading from the Control Relay. So I checked the parts source for a new one and the closest is in Miami and cost $230. Bummer!! This thing is smaller than a pack of cards!. I opened it up and no apparent cans were popped (capacitors). So whatever is bad is probably on the circuit board. And I can't get into it that far (tamper proof design). So now I'm on the hunt for a junked / wrecked RX300 to obtain parts from.

Larry In the back yard, under the oak.

Have just finished an extensive consult with tha boyz in tha bak. An them has come up wif two alternaters - er - coupla different wayz ta go here. One - ya kin do whut you is supposed ta do in the florida summer an stay under thet oak and not move much or two, ya culd just go down to tha kudzu store an have them ole boys fix it fer ya - shouldn't be no more than a couple thousand. Seems to me they charge more than the MB boys do to fix each problem, just have fewer of them, so their total take is about the same or a bit higher.

mcbrue under the bridge in the trailer down by the river

This is some module that contains a relay, or just the relay itself?

I would think could use any relay of equal or higher current rating from the auto parts store, and patch that in, if that is the failed component.

Typically these days such a relay is just a big fuse-shaped thing in the fuse block, on "ordinary" cars.

So, you're not only a clueless, obnoxious, a**hole, but you're a racist too. How appropriate is that!

So Glga, what is racist in the above? Sorry, but I don't understand your racist accusation here. Perhaps you think Floridians are a particular race and I am prejudiced against them? Or is it the reference to the Kudzu store - no, plants just don't equate to human status. Oh well ... guess I will wander off and see if I can find some cows to eat some kudzu - not that I have anyting against cows, as a matter of fact some of my best friends are cows.

Richard Nope! This is not your typical relay. This baby takes in both positive voltage and ground input, reads it, and outputs the appropriate amperage to the fan motor to control the speed. At least that's what I think is happening. At any rate, there are five or six capacitors mounted on top of a circuit board and another board underneath (that I can't get to without destroying the entire unit) and a heat sink on the back side. So it appears that this thing is regulating amperage to the motor to control speed. Sad part is, I'm not sure this is the only problem. The fan went to high speed and stayed there. It ran like that for about a week, then quit running altogether. When it stopped running, I tore out the kick panels and started looking for problems. But what if I replace this thing only to find out that something else was giving it a bad input? Control dial on the dash stuck in the open position and causing this unit to blow? At any rate, I am searching the junk yards for an organ donor. A buddy of mine spotted a wreck in a backyard yesterday on his way to work. Am trying to contact that victim to see if they will part with the remains.

Larry In the back yard, under the oak.

McBrue I think you miss the point. GI Georgia might be right! Maybe kudzu did come over onboard the Amistad. I never thought about that before!! If that's true, that would make them cows about as racist as the LAPD, abusing kudzu like that. Why, I might even have to suspend my experiments with kudzu. Since corn is in such short supply, what with ethonol demand, it's been hard finding enough ingredients to keep the "refinery" going. Have been experimenting with ground-up kudzu to make "green tea." Now I'm gona haf to stop, all because GIga pointed out that abusing kudzu is racist. Boy, I'm glad he did that. Keeps me out of a lot of trouble.

Larry In the back yard, under the oak.