Colder AC mod write up - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 12 Old 07-10-2011, 07:36 PM Thread Starter
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Colder AC mod write up

OK we were talking about this in this thread and there wasnt a real write up on it - so here goes
https://www.jkowners.com/forum/showthread.php?t=25391


First off, huge thanks to Rob4607 for the pics and walking me though it .
Seems like a major pain but really its not bad at all if you cheat like I did - me and cjb321 did 2 jeeps in about 10 min.

what you're doing is basically fooling the jeep into running the ac compressor just a little longer than usual by adding a small amount of resistance across its thermistor, making it "think" its a few degrees warmer than it really is so it cools a little farther.

Downside, possibly freezing the coils if you go too far see below

Anyway, on to the how-to.

we used:
http://www.radioshack.com/product/in...ductId=2062348
22K Ohm 1/4-Watt Carbon Film Resistor (5-Pack)
Model: 271-1339 | Catalog #: 271-1339
$1.19

so the parts are cheap, and you can experiment with different values if you want, 18k, 19k, 20k, 21k, etc

it helps to have a smallish and or flexible friend on this one (lucky you huh Chris?) - my 6'5" 330lb ass does NOT contort up under the dash too well anymore.

drivers side, pop the rubber panel out below the steering wheel and look up/in towards the center stack and you will see a little plastic plug with a grey jacketed wire coming off of it - its easy to spot, its the only gray jacketed small wire in there - DO NOT PULL THIS PLUG OUT OF THE AC PLENUM. Its a one time use plug and wont be happy about things, instead if you follow the gray jacket wires up, about 8" above where it comes out of the plenum theres a white plug in the wires clipped to the dash.
Use a flat screwdriver and pop the plug loose from its clip and it will reach down to where you can work on it. - reaching the plug to unclip it is where the small/flexible friend comes into play - thanks Chris!

This is the general area you'll be working in


this is what you're looking for



you want to attach a resistor across the 2 wires in that plug.

here's the cheat: the easy way, bend the resistor leads into a tight U shape around the resistor, jam them into the back side of the plug and wrap it with electrical tape. This is a good temporary method if you are trying different resistor values, etc.

a Better way, once you are happy with your resistor values/ac temps - strip back some insulation on the 2 wires, solder the resistor in, heat shrink/electrical tape it.



anyway, thats it!

contort, pop the plug from its holder, install resistor across the wires, tape, tuck it back up into the dash, enjoy colder AC.

Thanks again for walking me through it Rob!


here's some additional info...
https://www.jkowners.com/forum/showpo...1&postcount=16
Quote:
Originally Posted by jeeparoo View Post
its pretty easy though.. if you crawl in the driver side and look up under the dash there are 2 wires going into the side of the A/C plenum in the center stack.. those 2 wires go up to a connector that you can dislodge from its mount... you can then backprobe a resistor into the connector across the 2 wires.. this fools the computer into thinking that the coil temperature is warmer than it really is.. letting the compressor stay on a little longer...

too small of a resistor (lower number) and it stays on too long and will ice up (causing loss of airflow)..

too large of a resistor and it wont make much difference..

because the sensors are very different by nature.. thermistors vary a lot.. some people's Jeeps get ice cold.. others notice a warm / cold cycling feel from the vents...

it also means the resistor you need will vary.. somewhere between 18K ohm and 25 Kohm.. start with 22Kohm and work from there using a digital thermometer in the vent with the fan on 3rd speed... drive the jeep over 40 MPH and monitor the vent temperature..

if the vent temp drops below 40 very much you will freeze the coil.. (a rule is the coil is usually 8-10 degrees colder than the air at the vents)...

II run mine right at the edge.. in fact occasionally I notice excessive amounts of water draining after al ong drive which means I probably had a little ice on the coil... ive got a 22K ohm resistor on mine...
-Christopher


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Last edited by venom; 07-10-2011 at 07:57 PM.
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post #2 of 12 Old 04-21-2012, 02:04 PM
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thats a great idea and well needed too.

Ruben

07 JK Rubicon - Banks Cold air intake and Monster exhaust - ARB front and rear bumpers - Warn 9.5Ti - OME 4inch JK Lift - 33inch MTZ

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post #3 of 12 Old 07-01-2012, 11:51 AM
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I just did this mod using a 22ohm resistor.
I noticed with the jeep parked with AC on and fan at the lowest setting. The AC compressor is constantly on.
With the resistor out and same settings the compressor would cycle on and off. About 24sec on and about 8secs off then starts again.

Anyone else that did this mod experienced this? Should I be concerned that the compressor doesnt shuts off? Maybe use a higher ohm?

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Last edited by Chris85xlt; 07-01-2012 at 12:16 PM.
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post #4 of 12 Old 07-01-2012, 12:27 PM
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No, the compressor will shut off when the temp hits it's mark, the hotter it gets the more it will have to run, especially sitting in park or traffic. Try a shop fan in front of the jeep and idle it up a few hundred rpm and it will cool a lot faster and blow a bit harder.

All this mod does is "fool" the txv to see a different temp than actual to make it cooler.

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post #5 of 12 Old 07-01-2012, 12:53 PM
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Quote:
Originally Posted by Chris85xlt View Post
I just did this mod using a 22ohm resistor.
I noticed with the jeep parked with AC on and fan at the lowest setting. The AC compressor is constantly on.
With the resistor out and same settings the compressor would cycle on and off. About 24sec on and about 8secs off then starts again.

Anyone else that did this mod experienced this? Should I be concerned that the compressor doesnt shuts off? Maybe use a higher ohm?
I don't know anything about this mod, but I do know there is a big difference between a 22ohm and a 22kohm resistor. If you did this with a 22ohm, you might want to get the right resistor and replace it.
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post #6 of 12 Old 07-01-2012, 02:27 PM
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My bad.... I used a 22k-ohm


edit:
Got my hands on a temp gun and got ~10*F cooler then stock.
Compressor cycles like normal after hitting the colder temp.

Thanks! awesome mod

09' White JKU Rubicon with some stuff

Last edited by Chris85xlt; 07-03-2012 at 09:24 AM.
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post #7 of 12 Old 05-10-2013, 05:47 PM
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I dont get it. I can't tell where you putting the resistor. Maybe dumb but is it in line or goes from one wire to the other. Pics are not that great.

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post #8 of 12 Old 05-10-2013, 08:11 PM
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Bridging the two terminals across the plug if I remember correctly. Basically you are stripping both wires and jumping them with the resistor, all this does is change the resistance value of the txv making your Ac see a different temperature, I had to play with the resistors and still need to try a different one now as it will freeze up if I have it on low and full cold. And when I say I can get frost out I ain't kidding. 95 degree day, 85-90 % humidity and I can hit 30 degrees out of the vents. How did I know this thread would pop up again?!

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post #9 of 12 Old 01-03-2014, 11:28 AM
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What a great quick and easy mod and what a huge difference it makes - thanks a whole heap pal!!
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post #10 of 12 Old 04-13-2014, 01:48 AM
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Well,

I just found this and I'm done! What a great writeup! For some help for others, it took me a good hour to find the gray sleeved cable. So I hope this helps others:

If you sitting in the drivers seat, it would be the far back right area, of course you have to be almost upside down to find it, but I did!

I live in Phoenix and hope this helps. :-)

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post #11 of 12 Old 07-02-2014, 07:20 PM
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This work on all year models, like a 2014 ?
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post #12 of 12 Old 07-17-2014, 09:12 AM
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dumb ass question for an old writeup, but... would a 20K 1/4-watt resistor make the air conditioning run a bit colder or warmer compared to a 22k 1/4-watt resistor?
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