Cooling fan constantly cycling on/off - Subaru Forester Owners Forum
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post #1 of 20 (permalink) Old 02-08-2010, 06:10 PM Thread Starter
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Cooling fan constantly cycling on/off

Hello all. My '02's radiator fan is constantly cycling on and off, usually for very short periods (10 seconds or less). It starts as soon as I start up the car, whether it's 40 degrees out or 75. The engine revs drop noticeably when it cycles on. The engine seems to warm up normally and never gets over halfway on the gauge. Once the car is hot, the fan activity seems to be more normal, but still busier than I'd expect. So maybe this is normal, but my '98 didn't do it, nor has any other car I've ever had. Any ideas? I searched the forum but didn't see anything. TIA for all responses. PS moderators, if this would be better in the "Problems" forum, feel free to move it.

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post #2 of 20 (permalink) Old 02-18-2010, 05:02 PM
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Is your heater/aircon set to window defrost mode? If so, that engages the aircon to make sure the air blown on the windows is dry by chilling it first to condense out moisture/humidity. IN that mode, the cooling fans will cycle on and off frequently.

04 Outback 5MT
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post #3 of 20 (permalink) Old 02-28-2010, 10:48 PM Thread Starter
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No, it's probably been in every possible mode including no fan or a/c at all and it still cycles. It does sort of mimic the a/c compressor though, in that the engine revs slow down a bit with the added load. Resetting the computer didn't change anything. Oh well.

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post #4 of 20 (permalink) Old 03-10-2010, 07:59 PM
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Should the main cooling fan come on only when the AC is run or when the car reaches a certain temperature?

2000 Forester L
150,000 miles and beyond!
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post #5 of 20 (permalink) Old 03-10-2010, 08:28 PM
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Are the little green connectors under the dashboard connected? They shouldn't be.

2005 Obsidian Black Pearl XT w/4eat
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post #6 of 20 (permalink) Old 03-13-2010, 08:59 AM Thread Starter
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Superhero, no car (or motorcycle) I've ever had has had the cooling fan come on before it's needed.

Guroove, I feel like I'm being set up here but what little green connectors?

PD
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post #7 of 20 (permalink) Old 03-13-2010, 09:06 AM
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Quote:
Originally Posted by superheropunk View Post
Should the main cooling fan come on only when the AC is run or when the car reaches a certain temperature?
The fans will kick on with the AC and or when the car reaches a particular coolant temp. The AC will come on even if it's cold outside when you turn on the defrost. Also, if you are on the hairy edge of needing a recharge in the AC system it may be cycling on and off due to that. (maybe) There is a pressure sensor that when it sees low pressure in the AC system turns the whole system off to protect it from damage. The system not only circulates the R134a but also lubricant so if it runs while dry bad things could happen.

The green connectors under the dash, look here:

Why is this green plug not connected?

Peaty

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post #8 of 20 (permalink) Old 03-17-2010, 12:40 AM
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That's fixed it

I'd like to thank those who posted here as i have just fixed the problem of the cooling fans cycling on the Forester just recently purhcased from Ebay !

The other forester i had has now become a Murtaya , and that's receiving a new gearbox which should be longer in the leg than the origonal.

Many Thanks

David
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post #9 of 20 (permalink) Old 03-18-2010, 10:44 PM
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Care to share what the fix was? I have the same issue with my 05. Was it the green connectors?
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post #10 of 20 (permalink) Old 03-19-2010, 09:17 PM Thread Starter
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Quote:
Originally Posted by Peaty View Post
The fans will kick on with the AC and or when the car reaches a particular coolant temp. The AC will come on even if it's cold outside when you turn on the defrost. Also, if you are on the hairy edge of needing a recharge in the AC system it may be cycling on and off due to that. (maybe) There is a pressure sensor that when it sees low pressure in the AC system turns the whole system off to protect it from damage. The system not only circulates the R134a but also lubricant so if it runs while dry bad things could happen.

The green connectors under the dash, look here:

Why is this green plug not connected?
In my case at least, AC not on, no defrost, car cold, AC seems great when I use it (and I do 1x/month for maintenance reasons), assume green connectors aren't (no other issues as described in thread), fans STILL cycling

PD
SF, CA
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02 Forester S (now)
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post #11 of 20 (permalink) Old 01-08-2012, 08:26 PM
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Originally Posted by PDSF View Post
In my case at least, AC not on, no defrost, car cold, AC seems great when I use it (and I do 1x/month for maintenance reasons), assume green connectors aren't (no other issues as described in thread), fans STILL cycling
Ever figure out the problem?
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post #12 of 20 (permalink) Old 01-08-2012, 09:48 PM Thread Starter
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Nope. I've just grown to accept it as a quirk. The car has so few problems that I guess I shouldn't manufacture any.

PD
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post #13 of 20 (permalink) Old 01-08-2012, 09:52 PM
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My 11 does the same thing. Only turns off if I switch the air control to legs and dash.
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post #14 of 20 (permalink) Old 01-09-2012, 07:50 AM
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I noticed my 2000 L doing the same thing the other day while parked in the cold with the heat on. Guess i will ignore it as well
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post #15 of 20 (permalink) Old 01-09-2012, 11:18 AM
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It's one of two things.

1. Engine thermo fan temp sender is the wrong one for your model!

2. Cooling system thermostat is failing, blocked or damaged!

If it's the engine water thermostat failing to open at the correct temp! It's opening and closing way too late causing the fans to cycle at that opening temp.

It will eventually break apart and close shut giving you an immediate boil situation!

Watch it! You can cook your motor when it fails!
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