AC fan blowing slower than ever

[crabtruck]

Pretty soon ninja's going to put up one of those counter billboards about blowers...

I was away from forum for sometime after you were working on tranny harness.
You may want to check for wires damaged or "shorting" (leaking ) from oil damage.
Suggested you check voltage at blower not resistance,
since I don't think blower itself is intermitant.
.

[chengny]

After carefully studying the schematics, I think that I may have uncovered the root cause of your blower problem. Your truck did not come with one (a blower).

Sorry, just a small morning joke.

But serious, the drawings I looked at don't show anything at all about the blower. Why? I have no idea.

It is a completely acceptable test to go straight hot from the battery to the single blade that comprises the entire (other than the ground strap/wire) elecrical harness to the HVAC blower. Just pull the rubber boot off the fan casing and you will see a single spade terminal. With the female half pulled off, run a jumper from any convenient 12VDC source. If you don't want to break open a harness and the battery is too distant, use a regular battery charger. Attach the red/+ to the spade connector on the casing and clip the black/- to the grounding wire at the bolt on the firewall. Actually the polarity doesn't really matter. Since it is a DC motor - if you have them reversed, the fan will just run backwards for the test.


Flip the charger on and listen. At the 12 volt setting the fan should run at full normal speed. If you have a charger with a 6V option drop it to that setting. The fan should slow to half speed.

All the blower resistor unit is - it's a stack of 3 resistors that are cut in and out remotely at the dash board switch. At low speed all 3 are in series impeding the current flow to the motor. When you move the switch to low-medium, one is by-passed and there are two remaining in the circuit. At high-medium only one resitor is left. And when you move your selector switch to high the last one is removed and the motor coils see full battery voltage.

Unfortunately, the only thing that this test will tell you for sure is whether or not your blower is good.

But if you have a Fluke meter handy, you can take it one step further. Check that the correct voltage is being supplied to the feed wire from the resistor block. As you move the fan speed switch the voltage should jump up in 3 volt steps. 3 volts in slow, 6 in low-med, 9 in hi-med and 12 in high.

After these two quick diagnostics are complete you should have good idea of where the trouble lies.

But, and I know I sound like a broken record, whenever there is an electrical malfunction on a low voltage system always think ground, ground, ground.

And remember, the fan casing is plastic and cannot be used to complete the motor winding circuit.