Seeking wiring help/input - retrofitted GM A/C blower fan/motor in Civic


Old 04-30-12, 05:40 PM
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Join Date: Apr 2012
Posts: 2
Seeking wiring help/input - retrofitted GM A/C blower fan/motor in Civic

I hope some of you guys here can help me out. Seems this place has a good deal of knowledgeable people! I'll try to be as detailed as possible here to hopefully get some good tips/help. Long story short - the dash vent output on the older Civics (88-91) is weak. Even with a properly cooling A/C system the vent output is so weak that it won't keep you cool on a hot Texas day - the air will barely reach your face.

So, I retrofitted in a blower motor and fan assembly from the late 90's GM/Chevy trucks into my stock Civic blower box/assembly. With the help of my brother, we wired the new motor up with a Bosch style auto relay. The blower works fantastic and blows MUCH harder than the stock Civic setup. All speeds work perfectly through the factory climate control fan speed knob.

BUT - my concern is that the wiring at the fan motor harness gets a little hot. I don't *think* it's hot enough that it could melt, as I can touch it with my hands without getting burnt, or anything, but it is hot enough to slightly worry me. It doesn't seem to continually get hotter, rather, it warms up pretty quick and seems to stay at this same hotness-level for the duration of its operation. However, the longest I've had it running continuously is for an hour yesterday (and it seemed to stay at about the same temperature to the touch) but I suppose it's possible that after several hours of continuous usage it could get hotter.

Let me now explain how I have this wired to see if anybody has tips/suggestions/help. I'm no electrical guru but my brother is better than me at this stuff and came up with this for me. Here is the stock wiring schematic (click for full-size):

Here is how we have it wired up currently (forgive my crude drawing and please note I altered the positions of the pins on the relay for the sake of the drawing so as to not have my drawn wires have to cross eachother):

Now, I cut the male harness end off my old blower motor so that I can plug it into the female stock harness side. The female stock harness side consists of the blue/black and blue/white wires you see in the schematic. As you can see the relay is essentially wired in-line on the blue/white wire (this wire is about a 12 gauge wire). The blue/black wire is much smaller, it seems to be about an 18 or possibly smaller gauge. The harness here is what gets hot, and it warms up the blue/black and blue/white wiring several inches up the factory harness.

The relay wiring is all 12 gauge and the relay and its wiring does get a bit warm (which I understand is normal), but the "hottest" section is right at the factory wiring to blower motor harness I described above.

My questions (if anybody is still reading) -

1) First of all does how I have this wired look correct? If not, any other suggestions?

2) Is it normal for a blower motor wiring to get hot during operation? If not, is there an acceptable threshold of "hotness" level?

3) Lastly, if how I have this wired is copacetic, is there any "fix" for the hotness level? Like I said, it's all 12 gauge wiring except for the blue/black wire which seems to be about 18 or so. Is going with beefier wiring all around an acceptable "fix"?

I assume this larger motor pulls more power, likely contributing to this issue, but I've been unable find any ratings/specs for it. Going into this, I thought one of the benefits of the relay would be to prevent this exact situation with the hot wiring so I'm a bit puzzled in that regard.

I appreciate any input/tips/help.
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Old 04-30-12, 09:46 PM
Join Date: Mar 2009
Location: Texas
Posts: 1,051
It looks like you are overloading the ground side of the blower motor supply which is what the blower resistor controls. Why did you add the extra + battery connection rather than just swap out motors? Anyway my guess is that you are pulling more amps than the wiring was designed for including the blower motor resistor side. You are right to be concerned as it could end up at some point lighting up. You may need to install more of the GM blower motor wiring package to make it all safe including the blower motor switch and resistor.
Old 05-01-12, 07:15 AM
Thread Starter
Join Date: Apr 2012
Posts: 2
Originally I did just swap out the motors, but it didn't blow very hard and caused the factory wiring to get REALLY hot, which is why we introduced the relay. Like I said, I thought one of the benefits of the relay would be to keep the wiring from getting so hot, and while it's not as hot as originally, it's still hot enough to cause me to venture here for input.

One of the complications is that the stock Civic system is switched ground while the GM setup is opposite (early on, I manually grounded to fan motor to the chassis and not through factory wiring which caused the fan to blow full power anytime the key was in the "ON" position with the climate control fan speed switch having no control).

My brother pulled the AllData wiring schematics for the new Civics and it appears to be wired exactly how we have this wired, complete with relay. This is somewhat comforting because it appears that what we've done is at least in theory copacetic. I'm not sure why the older Civics used no relay but I guess that's moot now.

I noticed last night that the fan motor positive and ground wires themselves between the factory harness and the motor itself do not get hot. The relay and relay wiring gets warm, but the only thing that gets hot is the factory female harness on the body side 5-6 inches up into the loom (which is buried against the firewall). You mentioned it looks like we're overloading the ground circuit. Is that because of the smallish ground wire between the climate control and the body side female blower motor harness?

I was thinking this morning, what if I grab a spare climate control harness from the junkyard (the harness that plugs into the back of the climate control itself), de-pin the smallish ground wire and re-pin it with matching 12 gauge wire, bypass the small factory ground wire that follows along the wiring loom against the firewall, and wire that directly to the fan motor ground?

This way the ground would match in size the power line, be much shorter, and I would also be able to run it along the front side of the dash (albeit still hidden) for monitoring purposes and at the very least if it caused issues it wouldn't be buried in al the factory wiring and at least be a bit isolated should problems arise. Would this help with overloading the ground circuit?

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