E250 blower fan problem

[Rusty88]

Hi,
Lower 2 speeds on the blower fan not working. Only the hi speed is working.
Any ideas?
Thanks

[Selectron]

Hi, I'm not familiar with your vehicle but just in case it's a while before anybody else responds, I'll make a few comments.

The fact that your blower runs on the hi setting tells us several things:

• The 12V feed to the blower motor is good
• The ground return path is also good
• The motor itself is in working order

I had a quick look on Google and it seems that the Econoline uses the common arrangement of switching different values of resistor into circuit in order to vary the blower motor speed. So on HI speed there will be no resistor in series, and the motor will receive the full 12V, then on MID speed a resistor is switched into circuit and the voltage at the motor is reduced, and then on LO speed a still higher value of resistor is switched into circuit and the voltage at the motor reduces further still.

You have a failure in either the resistor pack, or the switch, or the wiring which connects those two items. Don't even think about replacing the motor, because your motor is good and the fault lies elsewhere. Of the three items which could have failed, I'd suspect the resistor pack first, then the switch second, and the wiring would be last on my list.

As I said, I'm not familiar with the vehicle so I can't help with component locations, but if you can get access to the back of the blower selector switch and can follow the wiring, then following it in one direction will lead directly to the resistor pack.

That pack will contain two resistors, and if they have burned out then there will be a strong burning smell from within. If you have a multimeter you can measure the resistance values between the single input lead and the three output leads. One of those will be a straight-through connection (for the HI setting) measuring 0 ohms (and we already know that connection is good), then one should have a resistance of around 0.5 or 1.0 ohms (for the MID setting), and the third should be slightly higher at around 1.0 or 2.0 ohms (for the LO setting).

My best guess is that your problem is within that resistor module.

[Selectron]

And here's a sketch of what I reckon that section of the circuit consists of. The items which are known to be good are indicated by the green line, and the areas where the fault could be are within the red boxes.

I haven't shown the 12V feed, nor the motor, nor the ground return because we know they're all good - it's just the resistor switching section which you need to concentrate on.

Notice that it would require two of the connecting wires to fail in order to lose two speeds, and it would require two poles of the switch to fail, to lose the two speeds, but because those resistors are connected in series, it would only require one resistor (the one on the right-hand side) to fail in order to lose both lower speeds, so that's definitely what I would investigate first.

[wetbehindears]

There is a resistor in the wiring right before the fan. On my 91 E-150 it is bolted to the fan housing under the hood. It has a four wire plug going to it and 2 screws hold it in place. A new resistor costs about $20 at ford. If the four wire connector is burnt or cracked, buy a replcement while your'e at the dealer about $25