Hey all, I've been googling my fingers off for weeks trying to figure this out.

AC/Heater blower motor in my 99 is stuck on medium speed.

Here's what I have done:
​Took apart control switch and cleaned contacts. All buttons on module work accept the recirculation (light comes on but reading I have done suggests that the button could still be why recirculation doesn't work)
Changed blower motor resistor.
Unplugged and plugged back in all the things. (blower motor, resistor, control switch)
So after all that, it's still stuck. What else could it be? Is there a relay somewhere that needs to be checked? Could the control switch be bad even though it's a simple circuit switch? All other functions are working perfectly, heat, ac compressor, direction control, etc. Thanks for all your smarts and assistance.

 

I thought the resister replacement is the cure for this. Humm...maybe a bad resister or wrong size ? Unlikely, but who knows.

 

I also that this. I don't think my resistor is bad though. I even tried one out of my brother's 4th gen max that is working fine and still the same symptoms. My Haynes manual was also no use.

 

Sounds like the ballast resistor is partially failed.... Once it's completely failed it goes to zero resistance and full speed in every position

 

Where is the blast resistor? I've never even heard of that. Different from the resistor next to the blower motor?

 

Do you have the manual controls or the auto climate controls? There is a lot of difference in the fan control.

One commonality is how the fan itself is wired. 12 volts comes from the fuses under the hood to the blower motor. To make the fan spin, the control panel supplies the ground. To give you different speeds, the control panel puts resistance between the fan and ground. Full, direct ground is high speed. No ground is off.

In the manual controls, the switch that you rotate has a separate contact for each of the fan speeds. Speeds 1 through 3 uses the blower motor resistor. Speed 4 is a direct ground to the blower motor, bypassing the resistor. I can visualize the speed switch being messed up and only giving you one speed, but that would be a real stretch of the imagination. Plus, I would think that the # 4 high speed would still work. The switch is replaceable in the control panel.

In the auto climate controls, the fan speed is controlled by a transistor that replaces the blower motor resistor of the manual controls. When you press the fan speed button on the control panel, you are changing the voltage on the control leg (or base) of the transistor.

The blower motor resistor of the manual control system and its counterpart in the auto control system, the fan control amplifier, are not interchangeable. They look identical but won't work in the wrong type of control system.

Without knowing which control panel your car has, I can't get too specific. If you have a voltmeter and can do troubleshooting, I can give you some things to check.

 

I have the manual temp slider and fan switch. I'm fairly certain the the part I replaced is the right one too because I ordered the one for manual climate controls. 4 doesn't work either. No matter where I set the switch it stays on medium. If it's worth anything, when this issue first popped up the fan was stuck on high. Same other symptoms, then after I took apart the switch, cleaned it out and put it back together it was stuck on medium. I've since replaced the blower motor resistor to no avail. Think it's the switch? I agree with your hypothetical analysis though so I'm confused.
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If you took the fan speed switch apart and this problem started after you reassembled and re-installed, you need a new switch. Possibly the wiper contact has broken free from the shaft.

 

It was stuck on high before I took it apart so similar problem I guess. But I'll probably still swap it anyway since I don't know what else there is to replace at this point. I'll update when that's done.

 

Stuck on high - that was your blower resistor. I've soldered mine twice.

 

That would be true for the auto climate control system where all speeds are controlled by the so-called resistor. In the manual system, high speed bypasses the resistor.

 

Okay. So I went and grabbed the control switch out of my brother's 96 and bam. Everything worked perfectly. I don't understand how that simple switch could have possibly gotten stuck on low speed when everything inside it was turning fine, but there you have it. Thanks everyone for the replies.

 

Thanks for letting us know how it turned out.