Power to Blower Motor Switch

[Steve1987]

Hi,
The blower motor fan is not working. I have attached a photo of the blower switch. I'm guessing one of these four wires should have power but none do. Off to the left in the background is a spliced brown wire that has power. It runs together with the four switch wires over to the passenger side of the cab. I can't find the spliced brown wire at the motor relay or the blower resistor connectors. I have power to both sides of the heater/AC fuse. Is power suppose to be present on one of the four switch wires?

The vehicle is a 1987 GMC 3/4 ton 4wd automatic with air conditioning that doesn't work. Thanks,

Steve1987

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[bucket]

I believe those wires just ground out the different speed circuits.

Is there no power at the blower motor? Is the ground wire to the blower motor still in place? And I'm assuming you checked the fuses?

 

[1987 GMC Jimmy]

We just had someone with the same issue, and the ground was dirty on the firewall side. I'd check the wire for rat chewing or other damage, as well.

 

[RustyPile]

I believe those wires just ground out the different speed circuits.

Is there no power at the blower motor? Is the ground wire to the blower motor still in place? And I'm assuming you checked the fuses?

Bucket, you're thinking of windshield wipers speed control. So yes, one of the wires should be hot with the key on. Except for Hi speed, power to the blower motor passes through the switch.. In Hi speed position, the switch powers up the blower relay.. That brown wire comes from the factory with a plug.. Over time, the plug connections go bad, so it's a common practice to do a permanent splice. Rig up a couple jumpers - one for ground, one for power.. Go directly to the blower to determine if it works or not. If it does work, you have circuit and/or component failure(s)..

Like Jessie said, blower issues have been addressed several times the past few weeks.. Steve1987, check through those posts, you'll find explanations, wiring diagrams, and troubleshooting techniques for getting your blower working.. This one should get you started..
http://www.gmsquarebody.com/threads/heater-issues.20081/

 

[Steve1987]

Thanks for the responses. I applied power directly to the fan motor from the battery through a fused jumper and it runs strong. I can not find power on any of the connectors at the switch, the relay, or the resistor with the truck running and the switch set to any position. The fuse is good. The spliced brown wire I mentioned in my first post does have power on it. And it does have its own connector as RustyPile said. I have downloaded the appropriate wiring diagram, but am having some trouble interpreting it. I have been looking at youtube videos to try and get the hang of it. Give me a few days to see what I can find. Thanks again. Steve1987

 

[RustyPile]

Thanks for the responses. I applied power directly to the fan motor from the battery through a fused jumper and it runs strong. I can not find power on any of the connectors at the switch, the relay, or the resistor with the truck running and the switch set to any position. The fuse is good. The spliced brown wire I mentioned in my first post does have power on it. And it does have its own connector as RustyPile said. I have downloaded the appropriate wiring diagram, but am having some trouble interpreting it. I have been looking at youtube videos to try and get the hang of it. Give me a few days to see what I can find. Thanks again. Steve1987

Two tools are a must have when doing electrical work.. A multi meter of some sort, and a test light.. Both can be had from your local auto parts supplier - AutoZone, O'Reillys, NAPA, etc.. If you don't have em, get 'em, and get back to us.. There are several guys here that are pretty good at electrical repairs, we'll help you interpret the diagram..

 

[Steve1987]

Problem solved. First of all I want to thank all of you for your responses. Second, I have to tell you that I had made all the previous checks with the control slide switch in the off position. What a bonehead! So all the measurements I took before are invalid. I did not realize that until I had changed the fan switch. Once I had moved the control slide switch off the off position, I had all my fan speeds except high. I had power to the relay coil (orange wire) but the relay was not working. I had taken the metal cover off the relay to verify that. When reattaching the connector to the relay it it started clicking on and off. That's when I discovered the black ground wire in the connector of the relay wasn't making a good ground. I removed it and the rest of the pins and cleaned them good with an emery board. It's all good now.

I couldn't put the original fan switch back in to check it as I had torn it apart and couldn't get it back together. I seem to do that a lot. The guy I bought it from didn't say the fan didn't work, but maybe that is something you don't volunteer. I'm sure I checked it though. Anyway, I have attached a picture of the relay plug showing the poor ground pin and the fan switch with the connector attached and voltages at each fan switch position.

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Wire voltages measured left to right with an uncalibrated digital meter.

switch
position Tan or blu dark wire w/stripe

low 6.8 0 4.5 14
med 13.6 0 8.8 13.8
hi 12.8 0 13 13.2
highest 14.4 14.4 14.4 14.4

Steve1987

 

[RustyPile]

AAAhh, don't worry about having your multimeter calibrated unless it's off several volts... A tenth here or a tenth there makes no difference.. Probably 75% of the time electrical problems with these old trucks is because a ground connection goes bad... You did good, Steve ---- real good...

 

[HotRodPC]

I 2nd @RustyPile 's comment. You did fine. Don't even worry about a few tenths in these trucks. Lengths of wires, gauge of wire, even age and a little corrosion in the wire inside it's coating can change voltages. If it's working, you did great. Call it a day and be thankful you have heat.

 

[HotRodPC]

BTW, Thanks for coming back with an update as to what got you fixed. These are the threads that become valuable to the forum and found in search engines to help others.

Post #7 is where members are supposed to be hitting the LIKE button.

 

[Steve1987]

Boy, that voltage information below the picture is hard for even me to understand. I will try to post a better layout soon. Thanks for the replies.
Steve1987
This is better.

 

[smoothandlow84]

Im glad you worked it out....now I need to tear back into my fan speed issue. I too still have no high speed and all of the parts have been replacec (blower fan, switch, relay, resistor etc). Time to re-check all of the wiring connections....again. With the age of the wires, I have a feeling that it's corrosion as well.

Thanks for the updated info.

 

[Steve1987]

You should have 12v or so at the fan relay on the orange, red, and purple wires with the fan switch set to it highest setting. Check the relay pins for corrosion also. I had forgot to mention that. Good luck.
Steve1987

 

[batcomm1]

You should have 12v or so at the fan relay on the orange, red, and purple wires with the fan switch set to it highest setting. Check the relay pins for corrosion also. I had forgot to mention that. Good luck.
Steve1987

Having the same issue here. No high speed but have all others, I do not have 12v on red or purple but I do on the orange...