Fan/ AC Issue
JK Newbie
Joined: Aug 2019
Posts: 2
Likes: 0
From: Apple Valley CA
Cooling fan turns on and off constantlywhen running the AC.
I replaced the low and high speed cooling fan sensors,the cooling temp sensor,put a new fan and radiator in my 08 jku and everything seems normal until I turn my AC on,that's when the fan turns off and on and since the AC overrides the engine temp when it comes to the fan it's causing me to overheat,if I drive with no AC it's fine,fan turns on based off of engine cooling temp. Don't know what I'm missing.
Thread Starter
JK Newbie
Joined: Jul 2019
Posts: 5
Likes: 1
From: Albuquerque, NM
I replaced the low and high speed cooling fan sensors,the cooling temp sensor,put a new fan and radiator in my 08 jku and everything seems normal until I turn my AC on,that's when the fan turns off and on and since the AC overrides the engine temp when it comes to the fan it's causing me to overheat,if I drive with no AC it's fine,fan turns on based off of engine cooling temp. Don't know what I'm missing.
JK Newbie
Joined: Jan 2025
Posts: 1
Likes: 0
From: Brookline, NH
Looks like I was wrong about always running the fan on hi-speed with A/C -- Just did another test and the fan was on lo-speed with a cold engine and cool nighttime temperature. Maybe it switches to high speed if the hi-side pressure is high enough, but less than the clutch cut-out pressure.
For the OP, there's also a temperature sensor on the evap (inside coils), the compressor clutch is de-energized when below a certain temperature. I'd start by observing the coolant temperature (via OBD2) when the radiator fan changes speeds (see temperature setpoints below). Next might be trending the hi-side A/C pressure and watching the compressor clutch.
For troubleshooting reference, at a standstill the fan starts lo-speed at 216F (reset 207F) and hi-speed begins at 223F (reset 216F). There's a small difference above ~28MPH, but these are the stock low-MPH values from my 2008 PCM's stock tune file.
For the OP, there's also a temperature sensor on the evap (inside coils), the compressor clutch is de-energized when below a certain temperature. I'd start by observing the coolant temperature (via OBD2) when the radiator fan changes speeds (see temperature setpoints below). Next might be trending the hi-side A/C pressure and watching the compressor clutch.
For troubleshooting reference, at a standstill the fan starts lo-speed at 216F (reset 207F) and hi-speed begins at 223F (reset 216F). There's a small difference above ~28MPH, but these are the stock low-MPH values from my 2008 PCM's stock tune file.
