2015 Jeep Wrangler Engine Fan and AC Compressor Run When It's Raining

[explorer2030]

The vehicle has the manual HVAC system, and I recently noticed it will cycle the AC compressor and run the engine fan on low only when it's raining outside even if the blower is in normal vent mode with defrost off and AC off. It operates as expected when it is dry outside where it will only cycle the AC when in defrost mode or when the AC light is on. I didn't see any mention of this exact behavior in the owners manual, but I was wondering if others are experiencing this and if it is considered normal operation or a malfunction.

I was trying a few different things to affect this behavior while the vehicle was idling including turning wipers on/off, blower on/off, defrost on/off, and cycling through the different vent modes. I noticed that if I push the AC button on/off the compressor stopped cycling, but nothing I did seemed to cause the fan to turn off until I shut the vehicle down.

 

[clinebarger]

Sensing humidity?

 

[dishdude]

On some vehicles using recirc will kick the A/C on.

 

[explorer2030]

I'm not sure that it has a humidity sensor since it was built with the the manual HVAC as opposed to the Auto HVAC. Is there any other way for the vehicle to determine when it's raining or high humidity without a humidity sensor? I had the recirc off when it was doing this.

 

[Audiman]

Is there any other way for the vehicle to determine when it's raining or high humidity without a humidity sensor?

You’ve got the wipers activated. It will also be fitted with a rain/ light sensor.

 

[explorer2030]

You’ve got the wipers activated. It will also be fitted with a rain/ light sensor.

I actually tested this by turning the wipers on and off, but it didn't seem have any affect on the fan or the AC compressor. Where would this rain sensor be located? I know that some of these Wranglers have a sun sensor, but I don't think I have one because mine doesn't have automatic headlamps.

 

[Audiman]

Have a look at the top of the centre of the windscreen, usually under the rear view mirror mounting.

 

[explorer2030]

Mine has nothing mounted on or around the rearview mirror. Its a manual toggle rearview mirror without any wiring going to it.

 

[Audiman]

Does the car have auto wipers or auto headlights? If not then probably won’t have the rain light sensor.

To be honest I assumed it would as pretty much any car from 2015 over hear has these systems fitted.

 

[explorer2030]

No it doesn't have auto wipers or auto headlights.

 

[Audiman]

Have a look the right of the steering wheel by your right knee hidden behind a plastic grate in the panel should be where the humidity sensor is located. a quick Google shows when you are describing is a “thing” the the wranglers do to lower cabin humidity.

You could confirm by boiling a kettle in the car and see if this triggers the A/C

 

[explorer2030]

Have a look the right of the steering wheel by your right knee hidden behind a plastic grate in the panel should be where the humidity sensor is located. a quick Google shows when you are describing is a “thing” the the wranglers do to lower cabin humidity.

You could confirm by boiling a kettle in the car and see if this triggers the A/C

From what I can tell that sensor is called the cabin air temperature sensor, and I can't find anything indicating that it can also detect humidity. I don't see a standalone humidity sensor in the list of sensors on the mopar.com estore for the vehicle. That is a great idea though to try putting some steam near it to see if it triggers the AC compressor.

Sensors for 2015 Jeep Wrangler | Mopar Estores

store.mopar.com

 

[WobblyElvis]

Chrysler mini vans have done this from around the year 2,000. Steam coming from the radiator as rain boiled off was a customer complaint that Chrysler addressed by changing the engine fan programming. Low speed, recent wiper use and certain engine temp equals engine fan on low.

The TSB for Chrysler minivans can be found here... https://www.chryslerminivan.net/threads/what-triggers-radiator-fan-runs-too-often.169503/page-2

 

[explorer2030]

Chrysler mini vans have done this from around the year 2,000. Steam coming from the radiator as rain boiled off was a customer complaint that Chrysler addressed by changing the engine fan programming. Low speed, recent wiper use and certain engine temp equals engine fan on low.

The TSB for Chrysler minivans can be found here... https://www.chryslerminivan.net/threads/what-triggers-radiator-fan-runs-too-often.169503/page-2

Very interesting and informative reading that TSB. Out of the 4 conditions mentioned for running the cooling fan I would not meet number 2 "The engine coolant temperature must be below the thermostat set point 195F". Mine has a 203F thermostat, but the coolant temps are always at or above that temperature cycling between 203F-210F. I also notice there is no mention of this water vapor strategy running the AC compressor when mine is doing this at the same time the fan is running.

 

[97K15004WD]

Chrysler mini vans have done this from around the year 2,000. Steam coming from the radiator as rain boiled off was a customer complaint that Chrysler addressed by changing the engine fan programming. Low speed, recent wiper use and certain engine temp equals engine fan on low.

The TSB for Chrysler minivans can be found here... https://www.chryslerminivan.net/threads/what-triggers-radiator-fan-runs-too-often.169503/page-2

Great find on this. I had a 2000 that did that - steam off the front of the van at stoplights in the rain. I wondered how they stopped that in later models.

 

[explorer2030]

I had a chance to do some additional testing, and it appears that the windshield wipers are a trigger for both the fan and ac compressor to start running. I started the vehicle and drove about 17 miles in the rain with the blower on regular vent, ac off and defrost off, but I never turned the wipers on for the entire drive. When I stopped to check under the hood, I found that both the fan and the compressor were off. I shut down the vehicle to go into a store and restarted after about 15 minutes, then continued on for about 10 more miles with the wipers on and the same blower settings. When I stopped a second time to check under the hood, I found both the fan and the ac compressor were on.

I still had about 15 more miles to get home, so I kept the vehicle running after the 2nd stop and turned off the wipers when I got underway. I checked again under the hood when I got home, and I found both the fan and compressor were on. It appears that once the fan is triggered by the wipers during a drive cycle, it will stay on until the vehicle is completely shut off or you drive well beyond 15 miles as stated in the TSB. I was able to stop the ac compressor either by pressing the ac button on and then off again, or by shutting off the vehicle.

 

[Audiman]

 

[KrisZ]

I actually find these features quite useful. Way back I remember seeing lots of cars with fogged up windows from the inside during rainy days it was quite common, not anymore.

Let it do it's thing, it only hurts the OCD.

 

[dishdude]

I actually find these features quite useful. Way back I remember seeing lots of cars with fogged up windows from the inside during rainy days it was quite common, not anymore.

Let it do it's thing, it only hurts the OCD.

The average driver would never even notice other than driving around with windows that aren't all fogged up.

 

[explorer2030]

You can hear the ac compressor cycling when sitting at a stop light, and the fan wind down as soon as you shut off the ignition. Most people that have any mechanical aptitude would notice it.