Blower motor / fan switch high current bypass (critique my wiring diagrams)

TrueTexas

TJ Enthusiast
Supporting Member
Joined
Feb 7, 2019
Messages
468
Location
TX
The blower motor connections are the first thing I worked on when I got my TJ in Jan of 2019. I redid the fan switch wires, the 3 pin connector wires, and blower motor relay as the harnesses for all of these had melted. Once I got the fan running on high only, I moved on to engine, tranny, brakes, suspension etc... and moved the HVAC system to the back of the list

Well I'm finally coming back to dealing with the HVAC system. I have ordered a blower motor, resistor, and resistor harness. I am at a point where I can roll the dice and swap the new resistor harness for the old melted one and install the new blower motor and call it a day or I can add relays to remove the High current going thru the switch.

I think I have it figured out option 2 and it would be about an additional $25-$30 job from here and maybe a couple of hours of work to do it right. I've already opened it all up so the toughest part is figuring out where to mount the relays.

Please take a look at my diagrams and let me know if you think I missed anything.

bypass 1.PNG


bypass 2.PNG
 
  • Like
Reactions: reddvltj
BTW, here is my current wiring job. Been so long, I had forgotten what I had done

IMG_20200502_162038.jpg
 
Bump...

With all of the posts and pictures about melted harnesses leading to the blower motor, I was hoping there were more of my fellow TJ owners out there that had done this mod.

So maybe we start with a more basic question...

Is doing this mod worth the effort if I am about to replace my blower motor (Valeo) and blower motor resistor and have already repaired the wiring correctly?
 
I did it just for personal peace of mind. I also put a switch in to cut power to the system when not needed. The factory (and other makes/models too) have some of the blowers running on low all the time (unless on 2 or 3 or 4), meaning there is no actual "off" setting.
 
The blower motor connections are the first thing I worked on when I got my TJ in Jan of 2019. I redid the fan switch wires, the 3 pin connector wires, and blower motor relay as the harnesses for all of these had melted. Once I got the fan running on high only, I moved on to engine, tranny, brakes, suspension etc... and moved the HVAC system to the back of the list

Well I'm finally coming back to dealing with the HVAC system. I have ordered a blower motor, resistor, and resistor harness. I am at a point where I can roll the dice and swap the new resistor harness for the old melted one and install the new blower motor and call it a day or I can add relays to remove the High current going thru the switch.

I think I have it figured out option 2 and it would be about an additional $25-$30 job from here and maybe a couple of hours of work to do it right. I've already opened it all up so the toughest part is figuring out where to mount the relays.

Please take a look at my diagrams and let me know if you think I missed anything.

View attachment 157970

View attachment 157969
Your diagram has ground to resistor to ground on the right side. One of those should be 12V. And assuming the switch supplies 12V, you have 12V to relay to 12V on the left. I think your red should be ground and your blue should be 12V.
 
Thanks @GEEP4ME - I am feeling a little less lonely in the endeavor.

Although I feel like the melted harnesses were an effect of the old blower motor going bad, my rationale is the same as yours. The added one is just the challenge of it.
 
@joelachr the system is a ground so the only 12v positive should be to activate the coil in the relay.

The left side of the essentially chooses which coil to activate.

The right side determines the path thru the blower motor resistor thru the ground

I am not showing the positive side relay in my diagram. That one is already activated when you turn the vehicle on
 
@joelachr the system is a ground so the only 12v positive should be to activate the coil in the relay.

The left side of the essentially chooses which coil to activate.

The right side determines the path thru the blower motor resistor thru the ground

I am not showing the positive side relay in my diagram. That one is already activated when you turn the vehicle on
Does the selector switch on the left side connect to ground or supply 12V?
 
@joelachr cool. Thanks for looking at it.

I know the original article from JP magazine was revised before it was finally deleted so I never got to read it fully. Looking at the way I put it together, I can't see an obvious flaws in it as the grounds thru the switch will run in the milliamp range. The higher current still goes thru the resistor bit that is unavoidable. However it will now have a better path. Meaning not thru the fan and mode swiches

The only one that may run higher is the AC but I haven't followed the wires for it yet so I'm not 100 sure how much current it carries. The green trigger in the 3 pin is pretty thin gauge (20) so I am guessing it doesn't carry a lot.
 
@joelachr cool. Thanks for looking at it.

I know the original article from JP magazine was revised before it was finally deleted so I never got to read it fully. Looking at the way I put it together, I can't see an obvious flaws in it as the grounds thru the switch will run in the milliamp range. The higher current still goes thru the resistor bit that is unavoidable. However it will now have a better path. Meaning not thru the fan and mode swiches

The only one that may run higher is the AC but I haven't followed the wires for it yet so I'm not 100 sure how much current it carries. The green trigger in the 3 pin is pretty thin gauge (20) so I am guessing it doesn't carry a lot.
Looks like that LG 20 gauge wire grounds a pin from the PCM so you're right, it's likely very low current. The compressor clutch is controlled thru a relay in the underhood power distribution box.
 
If I was to do it over, or make any other mods to mine, I would put an interrupt (switch) in the a/c trigger wire so that the a/c clutch doesn't engage when I have the blower completely off but have the select on defrost. Since my a/c isn't charged up right now, it's not actually doing anything except putting a drag on the engine when the compressor clutch kicks on. I have on occasion wished to be able to direct air to the windshield without the need to have the a/c compressor running and also without the blower motor on.
 
@GEEP4ME It sounds like there may be something way off with your HVAC system.

The AC compressor should not cycle when the system is turned off. Since you cannot set the fan selector to off in our Jeeps, I am assuming you have the mode set to off. In this case, the ground connection that sends a signal to the PCM should not be connected. You may want to disconnect the 3 pin connector on the HVAC control panel to see if the AC clutch continues to cycle. If it stops, you most likely have an issue in your mode switch in the HVAC panel. If it continues, the issue is further towards the compressor clutch. Pull the AC relay to see if that stops the compressor clutch from cycling and then you can move back towrds the PCM or towards the compressor to figure it out. The PCM needs the ground trigger and a ground from the high and low limit switches to allow the AC compressor to run.

You also indicated that your fan might be blowing when the vehicle is off. If so, that is also an issue as the fan gets its positive 12v from a relay behind the glove box (next to the green connector) that is triggered by accessory power and connects power direct to the battery via a 40 amp fuse in the underhoid fuse box. The blower motor should not be getting positive 12v when the vehicle is off.
 
@joelachr I see where the small green wire goes to the PCM. I was getting hung up at S103 - which turns out to be a splice for the 2 PCM triggers I mention in the post above to @GEEP4ME. You are right, looks like a low current wire.

I am not worried about the blend door wires as they are a separate harness and are in great condition so this should remove all of the high current from the HVAC switches and knobs on the dash.

I am assembling the parts in my Amazon cart as we speak. At this point, I am compelled to do this job as I have a new reason - a writeup so everyone who chooses to do this knows how to do it properly.

I have a strong background in mobile audio so this should be a relatively painless process.
 
Nothing wrong with my system. When you have the select on floor or panel, the a/c clutch is not engaged. When you turn it to defrost (or a/c), the a/c compressor engages (if the vehicle is a/c equipped). The a/c is what removes the moisture from the inside of the vehicle. I want to be able to turn it to defrost without the compressor kicking on.

And no, the blower is not running with the vehicle off. No sure where you thought that.

Running down the road, especially at highway speeds, the pressure/airflow at the cowl provides enough flow into the cabin at times to be enough for my needs. No reason to have the blower motor running during those times unless I want to crank it up. That's why I put the interrupt switch in.

I would also like to have the selector on defrost without the a/c compressor running. Even with the blower motor off, running down the highway, the natural flow into the cabin was getting really cold (when my a/c was charged) because of the a/c still running. Sure, I could adjust the temp to compensate, but again, why have the additional drag (and wear and tear) there if it's not needed?
 
@GEEP4ME . Gotcha. From the wiring diagrams, you should be able to add a switch directly to the light green wire on the 3 pin connector on the back of the HVAC panel as a "master" switch for the AC. That should allow you to override the AC trigger signal
 
Following up as I just installed this.

Notwithstanding the issues I am currently dealing with that are either related to the positive side relay/relay harness or new blower motor, this works perfectly.

Note in the attached pic, I don't have the lead that goes to the blower motor as I took the pic before I got a pigtail spade connector.

IMG_20200525_235521.jpg

And installed

IMG_20200613_203915.jpg

I mounted the relays to a piece of angle that is predrilled and mounted that to the 2 studs under the passenger side airbag. Fits perfectly.

Fan speed connectors are cool to the touch as there is only 600mv going thru them now. I am 100 percent confident there will be no more melted connectors or switch control there.
 
@bfabian76

Yes, still working perfectly.

Not sure if this thread captures it but I was still having some overheating wire issues. I finally went after looking for voltage drops. Turns out, the last leg of the +12v wire to the fan was pretty corroded. I replaced all of the +12v wire with 10 gauge from the battery to the fan. Problem 100% solved. Everything stays cool. Even ran the AC for 1hr in 90 degree Houston weather and all relays were still cool to the touch