Making the JK A/C Colder for <$2

ZMagic97

Explorer
As my 3rd summer approaches as a JK owner, I knew it was time for me to solve my A/C issues. My A/C always seemed OK, but never really good. It hit 100F in Phoenix yesterday, so I decided it was time to get moving on this project. The Jeep sat in the sun all day and I got in around 1800 to drive home. I noticed it was cool inside, but I wasn't as comfortable as I could be. After doing some reach, I found the following. I did not figure this out myself, just posting a "how-to" on information I found before.

Here's my temperature last night at 1900 after ~45 minutes of driving on the freeway at ~100F outside.

72...72?! That's pathetic and not cutting it in my book. I measured this temp inside the vent port of the center dash using a thermocouple.


It seems that the JK uses a thermistor inside the dash that taps into the airbox behind the A/C controls This thermistor controls when the compressor kicks on and off to reach the temperature the driver wants based off of the cabin temp. Apparently they have accuracy issues from what I've read. Removing the thermistor itself breaks it as it is a one time use connector.

Genius, right?

If you follow the thermistor connector (by the gas pedal, sticking out horizontally) you'll go up about 6 inches and find the connector on the side of the airbox, pull it off and disconnect it. The plug is white with gray insulated wires heading up towards the radio.

I made a jumper using a 22K ohm 1/5 watt resistor (5 pack at Radio Shack is $1.49 + tax, item number 2711339).

Here's the jumper I made. (I know, not the best solder job as I was in a hurry)


Here it is with heat shrink installed. I ran a continuity check after to make sure it was all good.


Installed on the plug going to the thermistor (sorry it's a bit blurry, but you get the idea)


Temperature reading the following morning after getting the dash back together. This was at around 0700, ~72F outside.


Conclusion: The ambient temperature outside is certainly different between the As Found and As Left readings, but I can tell the A/C is much colder now. Yes this causes the compressor to stay on. I don't see an issue with it myself as running it full time seems better that constantly going on and off. For those of you in more humid climates: going too cold may cause you to ice up the system. It can thaw out and work again just fine, so just be aware. I have heard of many people doing this for a year or so and are very happy. Again, I didn't come up with this, just doing a write-up with my own photos.
 

ZMagic97

Explorer
So I just measured again tonight about 15 minutes after I got home. With a hot engine and it reading ~102 outside I was getting air from the vents at 62F. I was sitting in the garage taking readings so the hot engine bay and garage may effect those numbers a bit. Either way a 10F drop for 1 hour of my time and $1.63 is way worth it in my book. I drove the Jeep about 80 miles today and could certainly tell the difference.
 

Stumpalump

Expedition Leader
That's brilliant! Years ago when computer controlled engines came out we used to add a resistor to the air temp sensor before the throttle body to trick the computer into thinking it was 30 degrees colder outside. That richened it up and advance the timing just enough that you could feel the increase in power.
 

wADVr

Adventurer
That's brilliant! Years ago when computer controlled engines came out we used to add a resistor to the air temp sensor before the throttle body to trick the computer into thinking it was 30 degrees colder outside. That richened it up and advance the timing just enough that you could feel the increase in power.
We also used to do a similar mod to the ECU temp sensor to trick the computer into thinking it was running slightly hotter than it was to allow the electric fan to kick on before it was too late an XJ thing..


Interesting mod for the AC, do you happen to know the temp difference the system is now seeing vs what it was before? I assume this resister was chosen to get you a certain temp reading and his reading should still be above freezing to keep the system from freezing up.
 

KaiserJeep

New member
Here's a trick to make BOTH your heater and A/C work better:

1) Hardtop Jeep: Buy and install a Hothead hardtop insulation and headliner package: http://hotheadheadliners.com/

2) Softop Jeep: Buy and install the Bestop Headliner for your softop: http://www.quadratec.com/products/11193_33XX_PG.htm

Disclaimer: Bestop is the Mopar softop supplier for the TJ and LJ tops, and these headliners fit either the original top or the Bestop RAT (Replace-A-Top). If you have another name brand, you may have to custom fit the insulation. Also, I do not know anything about JK model soft tops.

In addition to making your heating/cooling systems more effective, insulation also reduces heat gain in the hot sunlight.
 

ZMagic97

Explorer
I don't happen to know the difference it seems now and then. I chose the resistor one someone else s finding who used a potentiometer to find the best resistance rating.

It does seem like my system did take a little refrigerant yesterday which is helpful. I certainly don;t think there's a leak anything but I can get a small can of the stuff for $3 so I figured it was worth a shot.
 

nnnnnate

Adventurer
A few questions about this:

Is the white plug you show the one time connector or is that the actual thermister that you can't pull out? Am I understanding the process correctly that you place the jumper on the two wires that are entering the white plug? I am interested in giving this a try but don't want to do anything that can't be returned to stock. After adding the resistor do you plug everything back up or leave it unplugged?

Also, how much difference was there in the temp readings when switched from outside air to recirculated air.
 
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Longtallsally

Adventurer
I've not done any research on this, but I'll just add a bit more info to help the masses in understanding how the AC in a car works (and any solution I mention will be WAY more money and effort than what the OP has listed).

First off, it seems that there is something wrong with your AC to start with. Even at 62F, that is too warm and tells me a couple things:
- You were idling and not moving (the condenser needs a good bit of air moving through it to be effective- i.e. driving at a decent speed with clean air- with modern refrigerants)
- I think you might be down on refrigerant (based on the above)
- I might be a bit concerned about the lifespan of your compressor when it is asked to be constantly running (not to mention MPG and power loss- albeit minimal for both)

For me, in rebuilding and updating the ENTIRE AC system in an old BMW a few years ago (including fully removing, flushing individual components, and replacing/upgrading parts as well as switching to a legal refrigerant) I learned a lot more about the systems.
1) For truly best results with modern refrigerants, a bigger/more efficient condenser is the best option.
2) For low speed action, a higher speed or better condenser fan would help this process as well.
3) Properly running AC systems I think are supposed to have just above freezing air coming out: ~38F or so.

The OP didn't mention what year his vehicle was, so it's hard to research the system, and I don't know the differences in the systems when the new engine was introduced, but I do some checking on stuff based on the above prior to running to Radio Shack splicing in a resistor. I'm not saying this is a bad solution by any stretch- especially with living in AZ- but I'd make sure to account for all aspects of a system/solution prior to moving forward. Case in point, as was mentioned, the insulation aspect. When we have the soft top on, the AC has to work A LOT harder with the fan turned up 3-4 steps higher to keep things comfy in the cabin and you can feel the hot air penetrating even at speed through the top. With the hard top, after the vehicle is cooled off, we can generally leave the AC at fan position 2 given similar temps outside. This is a '12 JKUR with no insulation at all (other than a spiderweb shade).

All in all, I think this is an interesting discussion, especially as the JK has become much more creature comfort capable.
 

nnnnnate

Adventurer
I checked the A/C temp the other day after posting here. Ambient temp was 92* and my air was coming out of the middle vent at 48* with fresh air and 46* with recirculated. It appears that my system is in tip top condition.
 
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