Air Conditioner Performance
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JK Enthusiast
Joined: Apr 2009
Posts: 112
Likes: 0
From: Albuquerque, NM
the A/C issue is the fact the due to the way EPA measures fuel economy car manufacturers are required to test MPG with the A/C on.. so they tend to cycle the unit out when the output vent temp is around 50-55 degrees which is cool but not the ice bone chilling cold that some (including me) like...
Jeep uses an H-valve (a fake TxV sort of) and an evaporator temperature sensor to control the compressor cycling...
the evaporator temperature sensor is a wierd value thermistor... its not a standard 10k device... however it can be skewed allowing the compressor to stay in longer...
these devices typically have a 5% tolerance level in them which can result in different people having different results...
I ended up popping a 20K ohm resistor across (in parallel) with my sensor and am now getting 40-45 degree air on average from the vents.. an 18K ohm resistor dropped the vent temp to the high 30's however It also started to freeze the evaporator core.. so I backed off a little...
MUCH better than the original 50+ degree air..
because of the differences in the tolerances of the sensors you may need t play with tyhe resistor values a little to get it calibrated just right.... the lower the value resistor the colder the air although more risk of freeze-up and freezing up solid *CAN* damage the air-conditioner if left out of control.. the higher value resistor the less effect it will have...
id say 15k-25k ohms is the range needed..
-Christopher
Jeep uses an H-valve (a fake TxV sort of) and an evaporator temperature sensor to control the compressor cycling...
the evaporator temperature sensor is a wierd value thermistor... its not a standard 10k device... however it can be skewed allowing the compressor to stay in longer...
these devices typically have a 5% tolerance level in them which can result in different people having different results...
I ended up popping a 20K ohm resistor across (in parallel) with my sensor and am now getting 40-45 degree air on average from the vents.. an 18K ohm resistor dropped the vent temp to the high 30's however It also started to freeze the evaporator core.. so I backed off a little...
MUCH better than the original 50+ degree air..
because of the differences in the tolerances of the sensors you may need t play with tyhe resistor values a little to get it calibrated just right.... the lower the value resistor the colder the air although more risk of freeze-up and freezing up solid *CAN* damage the air-conditioner if left out of control.. the higher value resistor the less effect it will have...
id say 15k-25k ohms is the range needed..
-Christopher
Awesome info! Where is this thermistor? Sounds like its exactly the problem I'm having.
I found this post after a little bit of searching....
https://www.jk-forum.com/forums/stock-jk-tech-12/ac-jk-seems-lose-chill-every-couple-minutes-83188/
Last edited by Iblowstuffup; May 14, 2009 at 01:32 PM.
JK Super Freak
Joined: Jan 2008
Posts: 1,306
Likes: 3
From: Columbus, Ohio
the thermistor is located right in the evaporator plenum.. if you look up under the dash o nthe driver side.. right behind the center stack in the A/C plenum you will see a circular device sticking out with a wire coming from it and going up into the dash.. the thermstor snaps into the side of the plenum down low.. trouble is they use "use once" clips that are destroyed easily if you just try and pull it out... GENIUS from chrysler.. NOT!
the wire goes up to a connector fairly far up attached to the metal dash frame.. I used a door panel clip separator tool and popped the connector clip loose from the frame.. there was plenty of wire slack to pull it down.. I then backprobed the resistor into the connector.. across its 2 pins.. and electrical taped it so it doesnt short to anything...
you will want to put the resistor in.. make sure it gives good contact and DRIVE the jeep for at least 30 minutes or so.. dont just test it in the driveway.. you need some RPM's and also air across the condenser to make sure you arent getting it too cold... in my case i used a variable resistor until I got it just right then read the value of the pot and put the resistor in permanently and clipped the connector back to the frame and ive got nice cold A/C... in fact almost as cold as my 86 Monte Carlo HotRod.. (it pushes 36-38 degree air and doesnt freeze... I love GM's evaporator design....)
-Christopher
the wire goes up to a connector fairly far up attached to the metal dash frame.. I used a door panel clip separator tool and popped the connector clip loose from the frame.. there was plenty of wire slack to pull it down.. I then backprobed the resistor into the connector.. across its 2 pins.. and electrical taped it so it doesnt short to anything...
you will want to put the resistor in.. make sure it gives good contact and DRIVE the jeep for at least 30 minutes or so.. dont just test it in the driveway.. you need some RPM's and also air across the condenser to make sure you arent getting it too cold... in my case i used a variable resistor until I got it just right then read the value of the pot and put the resistor in permanently and clipped the connector back to the frame and ive got nice cold A/C... in fact almost as cold as my 86 Monte Carlo HotRod.. (it pushes 36-38 degree air and doesnt freeze... I love GM's evaporator design....)
-Christopher
Super Moderator
Joined: Sep 2007
Posts: 1,748
Likes: 87
From: Arizona
the thermistor is located right in the evaporator plenum.. if you look up under the dash o nthe driver side.. right behind the center stack in the A/C plenum you will see a circular device sticking out with a wire coming from it and going up into the dash.. the thermstor snaps into the side of the plenum down low.. trouble is they use "use once" clips that are destroyed easily if you just try and pull it out... GENIUS from chrysler.. NOT!
the wire goes up to a connector fairly far up attached to the metal dash frame.. I used a door panel clip separator tool and popped the connector clip loose from the frame.. there was plenty of wire slack to pull it down.. I then backprobed the resistor into the connector.. across its 2 pins.. and electrical taped it so it doesnt short to anything...
you will want to put the resistor in.. make sure it gives good contact and DRIVE the jeep for at least 30 minutes or so.. dont just test it in the driveway.. you need some RPM's and also air across the condenser to make sure you arent getting it too cold... in my case i used a variable resistor until I got it just right then read the value of the pot and put the resistor in permanently and clipped the connector back to the frame and ive got nice cold A/C... in fact almost as cold as my 86 Monte Carlo HotRod.. (it pushes 36-38 degree air and doesnt freeze... I love GM's evaporator design....)
-Christopher
the wire goes up to a connector fairly far up attached to the metal dash frame.. I used a door panel clip separator tool and popped the connector clip loose from the frame.. there was plenty of wire slack to pull it down.. I then backprobed the resistor into the connector.. across its 2 pins.. and electrical taped it so it doesnt short to anything...
you will want to put the resistor in.. make sure it gives good contact and DRIVE the jeep for at least 30 minutes or so.. dont just test it in the driveway.. you need some RPM's and also air across the condenser to make sure you arent getting it too cold... in my case i used a variable resistor until I got it just right then read the value of the pot and put the resistor in permanently and clipped the connector back to the frame and ive got nice cold A/C... in fact almost as cold as my 86 Monte Carlo HotRod.. (it pushes 36-38 degree air and doesnt freeze... I love GM's evaporator design....)
-Christopher
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Joined: Feb 2009
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