Radiator fan always runs when raining at stops

Status
Not open for further replies.
Joined
May 25, 2005
Messages
22
Location
Bay Area, CA
I have a 2014 Durango and I've noticed my radiator fan always runs when it's raining when I'm stopped or barely creeping along. It's just like if you have the A/C on in summer. This happens whether the engine is stone cold or hot and never fails to come on if just a light rain or down pour. I've tried every combination of things like lights, wipers, A/C on/off and nothing changes the behavior.

I've tried to reproduce it on dry days with a spray bottle drenching the grill and wheel wheels with water thinking it might be short in the pressure sending switch for the A/C but no luck. I have the service manual it mentions nothing of the sort. At this point I'm stumped if it's a bug or feature and the logic of it doing this if it's designed this way.
 
Of course don't bring it to the dealer as its under warranty
smile.gif


Anyway, Is your defroster on and/or do you have auto climate control? It may be part of a dehumidifier programme. OTW I would say you have a coolant sensor out of spec or similar.
 
Last edited:
Is the AC compressor kicked in as well? Could just be to dry the incoming air so your windshield does not fog, similar to defrost.
 
Does it have automatic climate control? Most cars now have a humidity sensor that kicks the A/C on without you knowing.
 
Originally Posted By: Brent_G
Is the AC compressor kicked in as well? Could just be to dry the incoming air so your windshield does not fog, similar to defrost.


No, I've turned the whole hvac system completely off and it stills does it.

I'll mention it to the dealer next time I'm there for something else but I'm just so curious about it in the mean time.
 
Originally Posted By: dishdude
Does it have automatic climate control? Most cars now have a humidity sensor that kicks the A/C on without you knowing.


Makes sense. It does auto climate but it still does it even if I turn off the whole system. However, it would not surprise me if Chrysler had a software bug to still run the fan when sensing high humidity even though the system was off.
 
Originally Posted By: vertrkr
Originally Posted By: Brent_G
Is the AC compressor kicked in as well? Could just be to dry the incoming air so your windshield does not fog, similar to defrost.


No, I've turned the whole hvac system completely off and it stills does it.

I'll mention it to the dealer next time I'm there for something else but I'm just so curious about it in the mean time.




EDIT: Nevermind had a slow moment here.
 
Last edited:
I knew a Honda mechanic once, he bought from his dealer either an old saab or renault, lots of fan relays, hard to diagnose and get parts, he just wired them to all run, all the time
 
Chryslers are notorious for running the AC when you think they aren't.

Either the fan turns two ways, one blue, one grey. Or the fan turns down to "low" which many think is "off".

Unplug one of the AC pressure sensors under the hood, or pull an AC fuse. If it kills the compressor, it might kill the fan to-- as freon pressure drives the fan sometimes.
 
Now this is WAY in the past but in my 1987 Dodge Daytona service manual there was a passage describing just this.

Apparently at certain temps where the dew point is low and there is high humidity it would pulse/run the radiator fan in this fashion. It apparently did this so that when the dew would evaporate off the radiator at a stop it would not seem like the car was overheating due to the steam rising from the hood. You can imagine a non-mechanical person thinking just that. They would see the rising steam and think OMG I am spilling coolant. The same reason coolant gauges are filtered now so we don't actually see the precise water temp.

I found it interesting that even in 1987 someone was thinking about that.
 
Last edited:
Originally Posted By: Thermo1223
Now this is WAY in the past but in my 1987 Dodge Daytona service manual there was a passage describing just this.

Apparently at certain temps where the dew point is low and there is high humidity it would pulse/run the radiator fan in this fashion. It apparently did this so that when the dew would evaporate off the radiator at a stop it would not seem like the car was overheating due to the steam rising from the hood. You can imagine a non-mechanical person thinking just that. They would see the rising steam and think OMG I am spilling coolant. The same reason coolant gauges are filtered now so we don't actually see the precise water temp.

I found it interesting that even in 1987 someone was thinking about that.





Back in '87 cars still had real grills and yes you would sometimes see the steam.


To the OP ..does the fan come on with the wipers? Just curious.Maybe it is just a humidistat.
 
Originally Posted By: FL_Rob
Thermo1223 said:
Back in '87 cars still had real grills and yes you would sometimes see the steam.

To the OP ..does the fan come on with the wipers? Just curious.Maybe it is just a humidistat.


Tried that, I've turned everything that can be turned off and the fan still runs. The owners manual does mention you might see steam from the grill on rainy or humid days so I don't think they are trying to prevent that by running the fan.

At this point I'm guessing it's a humidity sensor but it's odd the fan still runs even though I totally shut off the climate control.
 
Possibly because they have the temp set higher for efficiency,as all new cars have,the programming on the fan is right there on the edge of being energized by the computer ,thrown in stop-n-go /creeping and you could have what you describe.
 
I finally got this fixed. Turned out to be a loose/partially connected wire for the PCM low speed signal wire at the fan module. I had to wait almost a year for another rainy day in California to bring it in so I know they could reproduce it.
 
Turns out that didn't fix it but I finally have an answer to end this story. My service manager heard back from Chrysler engineering and they said it is working as designed. Engineering said when it's raining they expect you to use the A/C to clear window fog so the fan is always running in anticipation of the A/C being used. There is a humidity sensor. Sounds like a waste of energy to me as in my climate my window don't always fog when raining and why the fan can't just stay off until the A/C is in use is beyond me but there you have it for better or worse.
 
Last edited:
Status
Not open for further replies.
Back
Top