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How to wire relays into a Jeep TJ Climate Control Unit
1997-2006 Jeep Wrangler TJ (this job is being done on a 2001 Wrangler without A/C)

Pictures here: http://www.mediafire.com/folder/2tf7ry2m7wqnx/TJ_HVAC_Fix

I found some threads on this topic and really got the idea from JP Magazine's "Jeep Fire Prevention", which they revised in 4x4 Garage Spring 2013 edition, and explained that their original fix sucked. I believe they had issues with their set up due to them not wiring a master relay for the vacuum switch. Without doing this, there is still high current passing through the unit. I've seen plenty of discussion on this topic where people were only wiring 4 relays, but the idea here is to keep resistance from the HVAC unit, so why not put a relay between ALL power traveling through the unit, right?

This paragraph is mainly for those that don't understand why we're doing this:
To explain... The blower fan bushings wear out after time causing resistance, which causes heat. This resistance causes too much power pulling through these cheap switches. This is the same reason we use relays (solenoids have the same function as a relay) between winches and off road lights. The relay performs the same function as any switch, except that the relay is preventing the need for the high current to travel through the switch. We're wiring in relays to the HVAC unit to prevent the current from traveling through the HVAC unit. Most manufacturers set up HVAC systems without the relays for the switches, except for companies like Rolls-Royce. Some will use a relay only for the high speed fan setting, which does not pass through any resistors on the way to the blower motor. I hope this brief explanation helps a bit.

INGREDIENTS

(5) 30/40A amp relays
I bought these from Amazon: AGT (5 Pack) 30/40 AMP Relay Harness Spdt 12V Bosch Style (40AMP-HRNS) But there is an extra pin 87A, which I popped out of each relay, so they weren't in my way. Doesn't matter, as long as you get 30/40a relays
Soldering Gun
Solder (.062 dia. 1.5 oz)
Heat shrink tubing (a few different sizes), and a lighter or heat gun to shrink the tubing
Soldering Flux
Some red power wire with a 10 amp inline fuse with some way to connect to your battery
Some black ground wire
Some zip ties to make it pretty

IF YOUR PLUGS ARE FRIED, YOU'LL ALSO NEED
Replacement pig tails for your plugs
OR
Female Spade Connectors and epoxy
****ALSO****
You definitely want to make sure you replace either your HVAC control unit, or the switches. You may also want to make sure you replace your blower motor resistor (check the wiring too) and your blower motor, or test the resistance on the motor (JP wrote something up on this). At least your HVAC control unit will be safe without a new blower motor, but you may need it if you want heat. The harnesses that plug into those switches are a whole other issue. The Fan switch pig tail is $47, and I couldn't find the vacuum switch pigtail anywhere. I got lucky and was given a used dash harness with the fan switch plug, but no vacuum switch plug. I'll be making something using female spade connectors for this.

This write up is only showing how to wire in relays, but I will provide some part numbers:
PART NUMBERS
HVAC Control Unit
55037472AB 1 without A/C
55037473AB 1 with A/C
Vacuum Hose Harness
05013830AA 1 without A/C
05013831AA 1 with A/C
Vacuum Switch
05013832AA 1 without A/C
05013833AA 1 with A/C
Fan speed Control Switch
05011214AA
Blower Motor Resistor
04864957
Fan Switch Harness Pigtail (Morris 4x4 has these for $47, yuck)
68052589AA

Colored LED Lights?
If you're shopping online, and you're interested in colored lights, now would be a good time to grab three T4 LED lights for your HVAC unit. I bought these from Amazon: HOT SYSTEM T4 Neo Wedge LED Bulb for car Instrument cluster panel Blue 10-pack. I found that they were loose when I installed them, so I arched the pins up toward the led a bit and bent the arch down. This worked perfectly for me.

MAKING THE RELAY CHAIN
My Bosch style relays came with sockets that plug together, so I didn't have to tape them together. Like I stated before, these relays came with an extra terminal 87A, which we're not using, so I removed these. If you are using this style relay, you can use something pointy to press the pin from the flat side in and pull them out, or just snip 'em. If you've done your research, you may notice that other people may be wiring the relay terminals a bit differently. Just know that there are a couple of ways to accomplish the same thing using relays. Also, note that I had to move some of the wires, so the colors will not match up even if you have the same exact relays as me. I will be referring to wires by terminal numbers, not by color. So before we get started, make yourself a chart of terminal numbers and correlating wire color, so you don't have to keep checking. You may need to unplug the relay to see the terminal numbers.

Here's how mine are color coded (I had to change it around a bit)
Terminal - Color
30 - Yellow
85 - Blue
86 - Black
87 - Red

On all of these connections, I used solder, then heat shrink. Here's my soldering method:
1. Put a piece of shrink tubing on the wire before soldering
2. Dip each wire and the solder into flux
3. Add some solder to each wire individually
4. Heat all wires being connected while holding them together, once connected give a second to cool
5. Move shrink tubing over exposed wire twisting gently over the solder
6. Heat both sides of shrink tubing until tight

Keep in mind during this procedure to not have too much bulk of wires, but enough to work on it. There isn't too much room in the dash. You can see in the picture that I have quite a bit. You can probably do a better job than this.

Connect all 5 wires from terminal 86, leaving some length on one of the wires to ground out later.
Connect all 5 wires from terminal 30 (these are just chained together, and don't go anywhere else)

FAN SPEED SWITCH WIRING
For this next part, you may want the color codes of the Fan Speed Control Switch (speed 1-4 lowest to highest):
1 Tan
2 Light Green/Light Blue
3 Light Blue
4 Brown/Tan
Dark Green is not a fan speed and will be explained later

The fan speed switch should be snipped leaving some wire on either end to reconnect in this next part.

Individually connect each of the 4 speed control wires coming from the switch to terminal 85 on 4 of the relays
As you can see, I labeled the relays from speed 1-4. The fifth relay will be our "master relay".

Now connect the terminal 87 to the harness wires for the 4 speeds. On each relay, the wire color coming from the fan switch into terminal 85 should match the color that terminal 87 is connected to on the harness.

We'll need to run a separate power to the unit. Connect a wire to the battery, and run through the firewall. Use a rubber grommet if you're going through metal, or you'll have trouble in the future. The 10 amp fuse should be close to the battery. I wasn't using my subwoofer, so I checked for voltage, and used a power wire for that, but my heat only works with the radio on. I'll fix this once I add my accessory fuse box.

Connect the new fused power wire to one of the thick dark green wires in the dash harness (these two are in a loop), and also to the dark green wire on the fan speed switch.

VACUUM SWITCH WIRING
The vacuum switch has three wires. Black, dark green and light green. I'll be referring to these colors, so make note of the colors on the switch. Don't clip either green wire on the harness if the plug is good. We'll only need to clip the black wire, leaving some wire to connect to.

Connect terminal 85 from the "master relay" to where the black wire went on the vacuum switch
Connect terminal 87 from the "master relay to where the black wire went on the dash harness

*These next two steps can be skipped if you haven't clipped the vacuum switch harness
Connect the other thick dark green wire from the dash harness to where the dark green wire went on the vacuum switch
Connect the thin light green wire from the dash harness to where the thin light green wire went on the vacuum switch This light green wire is only needed for use of A/C I believe, which I don't have or care to. I do have it connected though.

Remove your power fuses before completing the circuit.
Connect the chained grounds (terminal 86) from the relays to a ground. I shared a ground under the passenger side front speaker.

Check your work and then replace the fuses. Now try it out, and I really hope it works for you. Check the speeds, the settings on the vacuum switch and the lights before putting it back together.

Tidy up your wires with some zip ties and carefully put your climate control unit and relays into the dash.

Please let me know if this helped you and make an account if you don't have one. I've used this site to help with a lot of questions I had, and I really wanted to make a good complete write up for this topic. Kind of paying it forward, ya know! Please also let me know of anything you see that can help make this better.

SOURCES
First and foremost, we have to give a big shout out to Jonny B for his brilliant work. Without him, I wouldn't have been able to do this. It pays to have an electrician before jumping into a job like this.

How to Wire 4 Speed AC Blower Relay (We have a different configuration than this):

http://www.fourwheeler.com/how-to/electrical/154-0710-jeep-fire-prevention/photo-01.html#1 (click through the photos and text will be underneath)

http://www.fourwheeler.com/how-to/154-1205-safe-heat/
 

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JBTJ, Thanks for the message. Do you recall how yours are wired?
This is how I wired mine about 10 years ago.

Parts used for the mod so far are: BOSH 40 amp relays x4, 12 gauge wire-15ft, heat shrink tubing, 12 gauge push on terminals .025 inch x16, 12 gauge ring terminal x2 (for battery and ground connections). I chose to solder all connections instead of using butt connectors and covering those connections up with heat shrink tubing. Should be more permanent.

I started by laying all 4 relays in a 2x2 configuration on my work bench. Then I labeled them 1 thru 4. I then daisy chained all the 12v connections together, terminals (86) and all the ground connections, terminals (87) This leaves terminals 30 and 85 open for which they will get spliced into the wire harness of the JEEP. This is what I call my harness.

Locate the fan speed switch behind the panel and gain access to it. You may have to unwrap some black tape to get to the wires. I started with the 4th speed wire, BR/TN I make the cut just past the switch about 2 inches. The side from the switch I connected to terminal 85 of the relay harness, this provides the signal to energize the relay. The other side of this wire goes to the resistor block/blower motor, I connected it to terminal 30 of the relay harness, when the relay energizes a ground will be applied to the resistor block through the BR/TN wire. 12 volts is needed for the relay to energize, I got this from a 12 gauge 30 amp fused wire that I ran straight to the battery or if you prefer a switched 12 volt connection within the dash and connected to terminal 86 of the relay harness. I then connected a 12 gauge wire to a good ground underneath the dash and ran it to a terminal 87 of the relay harness. That should complete the installation.

Repeat the process above for the other 3 speeds.
3rd light blue wire
2nd light green wire
1st tan or white wire
 

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My issue is with the dark green wire on the vacuum switch, where the snap-on connector has a black, light green, and dark green wire. The middle post connects the green wire, and the female end of it, in the plastic connector, is melted. I've seen a few pics of this on this forum, so I know it is somewhat common.

My question has two parts. One, does anyone know the name for this type of connector? And Two, is there a way to disconnect the individual wires from this connector? I've hinged the connector shell open to expose the female ends, but I can't get them to come out of the plastic shell.

Thanks.
 

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My issue is with the dark green wire on the vacuum switch, where the snap-on connector has a black, light green, and dark green wire. The middle post connects the green wire, and the female end of it, in the plastic connector, is melted. I've seen a few pics of this on this forum, so I know it is somewhat common.

My question has two parts. One, does anyone know the name for this type of connector? And Two, is there a way to disconnect the individual wires from this connector? I've hinged the connector shell open to expose the female ends, but I can't get them to come out of the plastic shell.

Thanks.
I simply cut off the melted black connector and soldered on new push on connectors and covered them with heat shrink tubing, the reinstalled onto switch.
 

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Discussion Starter · #10 ·
My issue is with the dark green wire on the vacuum switch, where the snap-on connector has a black, light green, and dark green wire. The middle post connects the green wire, and the female end of it, in the plastic connector, is melted. I've seen a few pics of this on this forum, so I know it is somewhat common.

My question has two parts. One, does anyone know the name for this type of connector? And Two, is there a way to disconnect the individual wires from this connector? I've hinged the connector shell open to expose the female ends, but I can't get them to come out of the plastic shell.

Thanks.
This is the fan speed switch, which may also be called speed selection switch. The other switch is the vacuum switch.

The method I used on this three connection switch worked out well for me. I wasn't about to spend 47 bucks on the pigtail which Morris4x4 sells. I clipped the wires from the harness and I used insulated female spade connectors on the two outside connections and a non-insulated for the middle. A little epoxy and you have a home made harness.
 

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Thanks guys, for my next project. So we need to add 4-5 relays to improve the stock HVAC.

And another thread suggests we might add a relay to reduce power draw from stock headlights, since there's " 'excessive' current draw through the switch and wire loom connector, generally because power provided to the headlights/fog lamp circuit flows directly through the multi-function switch at the steering column (bad design). Ideally, this circuit should have been designed to relay/switch battery current to the lighting system. High current draw lighting can cause issues in a short period, or stock lighting can cause this issue over years of use."
 

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Thanks guys, for my next project. So we need to add 4-5 relays to improve the stock HVAC.

And another thread suggests we might add a relay to reduce power draw from stock headlights, since there's " 'excessive' current draw through the switch and wire loom connector, generally because power provided to the headlights/fog lamp circuit flows directly through the multi-function switch at the steering column (bad design). Ideally, this circuit should have been designed to relay/switch battery current to the lighting system. High current draw lighting can cause issues in a short period, or stock lighting can cause this issue over years of use."
No that's over kill. I can't remember right off the top of my head how I did mine, but it only requires one relay. The switch in the dash panel controls is the weak link. It heats up and melts and takes others things around it with it. I'll look it up after work today and show you how to do it.
 

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No that's over kill. I can't remember right off the top of my head how I did mine, but it only requires one relay. The switch in the dash panel controls is the weak link. It heats up and melts and takes others things around it with it. I'll look it up after work today and show you how to do it.
Yes, thanks, I believe you are correct

Maintenance procedure #1: buy the books

So I finally bought the books for my model year, 2006, and it says I already have a factory relay on the HVAC blower

Knowledge is power !
 

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I’m in the process of putting the 5 relay system
I’m not sure of the DK Green wire from the vac switch to fan control
It mentions the power to the dk green
I may be miss understanding won’t this give a dead short through the vac switch?
I have the hvac wire diagram and can understand that the power excites the relay when the vac switch is cycled
Which sends power to the relays through the switch positions and through the chained ground out.
Please clear this up for me
Thx in advance
Phik
 

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Got it figured out.
I didn’t see that all the grounds on the vac switch are before the switch side of the relays ( harness 87)
Need the 12v power to trigger the 12ga black wire connected to the 85 and is triggered when the switch is activated through the contacts in the switch (green wire ) connected to the 12 v fused.
And the a/c has 12 v coming to the small green wire when it’s in contact on the a/c settings on the vac switch (dk green and the small green)
The black and DK Green trigger together past the a/c mode through the rest of the positions
 
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