blower motor, only speed 4

[flyboy1100]

i replaced both the relay and the resistor today in an attempt to fix this, and still only 4 works, occasionally the others will work too.

how likely is it that it is the switch in the dash at this point? i'm not sure where else to be looking.

 

[flyboy1100]

How do I test the resistor? Just need pins and ohm values

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[flyboy1100]

this could be it too i guess, didn't realize i could buy this part seperate

http://www.ebay.com/itm/ACDelco-15-...Parts_Accessories&hash=item5667e0c998&vxp=mtr

 

[89Suburban]

Very likely the switch. They take a beating over the years and actually melt on this inside from the high current passing through them. A great mod for these trucks would be to install a relay setup for the heater controls.

 

[flyboy1100]

Very likely the switch. They take a beating over the years and actually melt on this inside from the high current passing through them. A great mod for these trucks would be to install a relay setup for the heater controls.

Unfortunately im familiar with something like that because I just did it 5 months ago on my 2012 Subaru. Lame.

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[89Suburban]

Unfortunately im familiar with something like that because I just did it 5 months ago on my 2012 Subaru. Lame.

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It's on my to do list, less heated wiring in the dash waiting to burn the truck down.

 

[flyboy1100]

new switch, still flaky at best at all speeds except 4. i cleaned up the ground (didn't need it but was worth a try) voltage at the resistor seemed good,

i'm really wondering about the wire harness at the relay or if i got a bad relay.

i don't think it is the motor, i suppose it could be, but when i wasn't seeing power consistently on the purple wire that makes me wonder

 

[chengny]

There are two switches in an AC equipped control panel. There is the blower speed switch (shown in the link above) and there is also the "selector switch".

The hot wire for the entire HVAC system (from the fuse block) goes first to the selector switch. From there it splits into two brown and white wires (also a light green wire that feeds the compressor clutch via the low pressure switch - never mind that).

One brown/wht supplies the blower switch and the other supplies the common side of the resistor block. Make sure you are getting 12VDC at both these places.

The selector switch is incorporated into the vent control (where you select MAX AC, heat, defrost, etc) portion of the control panel. It is in the back and is horizontal.

 

[flyboy1100]

Thanks will try to check that this weekend.

question though, if that wire is powering both switches, and fan speed 4 works 100% of the time no matter what, how could it be the other switch? I will still test it as I have nothing else to try but doesn't make sense to me.

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[chengny]

It would appear, from what I read above, that you are looking for a loose connection or a broken wire. In this case it is best to methodically ring the circuits out - starting at the initial power source and working down the line - until you find an area of intermittent or low voltage.

A couple of things:

1. When the selector switch is set to MAX AC, blower speed goes to HIGH.
2. When the blower speed is on HIGH, the resistor stack is by-passed. That is usually the way a bad resistor stack is diagnosed - fan only works on high.

3. Both the resistor pack and the blower relay need to see full battery voltage. The resistor gets that 12vdc from the brown/white wire discussed above. The blower gets it from the big red wire that connects to bthe firewall junction block.

BTW - did you check the ground connection from the blower relay/contactor - for clean/tight connections and continuity?

 

[flyboy1100]

Yup, even cleaned them up for the heck of it.

I have been doing all my testing on the "vent"setting. Sometimes when I get 3 to work it will almost pulse. IE run for a few seconds, then stop and before the motor spins down start again.

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[chengny]

I was under the impression that the blower motor "known good". Now I see it is still on the list of possible suspects.

You need to determine if the blower is capable of continuous service (at least for a minute or so).

Simple check:

Pull the single hot wire off the motor and run a jumper from the battery positive. Alternately you can supply the voltage with a non-feedback type battery charger. You can do this with the fan still mounted.

With 12VDC applied it should crank up and blow air like a ****!

If it runs, but seems to struggle, fabricate a temporary ground wire. Run is as shown below:

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Remember, unlike straight heat set-ups, the fan housing on AC equipped trucks is made of some kind of plastic or fiberglass. Consequently the blower motor cannot be grounded to the airhandler. An auxiliary jumper wire is required.

This is in addition to the blower relay ground discussed above. They both ground to that same screw on the firewall.

 

[flyboy1100]

Setting 4 works perfectly every time, no weird cutouts. Only happens sometimes on slower settings. Seems like it will do it a few times, then run perfect. But if I switch back to 4 then to 3 it will maybe work, maybe be intermittent or just not work at all.

Motor was new last fall, but of course doesn't mean its still 100% good.

Electrical gremlins suck.

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[chengny]

When on the high setting the blower windings are getting full battery voltage. As the lower speeds are selected, the resistors within the resistor pack drop that voltage. It is probably something along the lines of:

Speed 3 - 9VDC
" " 2 - 6 VDC
Lo Speed - maybe only 3VDC

In an electrical circuit, the higher the potential (voltage) in a conductor, the greater it's ability to find a path to ground. That's why spark plugs can arc across a .0050" air gap - the electrode is at 40K volts.

So at say 3 volts, while that is plenty on the "inlet" side of the windings, it may not be enough to overcome the resistance to ground. The electrons stop, and so does the motor.

You know what I mean right?

 

[flyboy1100]

Yes. I am going to redo the purple wire to the fan as the relay side was corroded, the connectors should be here today.

Then I will double check power at the switches, and finally replace the fan.. If required



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