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2016 Subaru Outback 3.6R Limited
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As in the title, I have an 05 Outback 2.5i and I'm wondering about the behavior of the cooling fans.

I wouldn't be interested except that yesterday, in about 95F weather, my car hit the 3/4 mark on the temp gauge.

The situation that led up to this: a medium length ride through a fast food drive-thru (maybe like 5-7 minutes in total) with the a/c on (I noticed in the drive-thru that the a/c wasn't working so well). Upon parking the vehicle, I looked under the hood to see what the coolant looked like (a darker, but clear green) and to see if the fans were running. In this situation, only the main fan was running (the a/c was still on). On my drive home from work, same degree outside but no stop-and-go and the temp gauge never moved above the middle.

Today, I turned the car on with the a/c and I noticed that no fans were running (car was started cold). Then, later in the day, I turned on the car with the a/c on and both fans were running (car was started cold). Then, 10 minutes later I turned on the car with the a/c on and only the main fan was running (car had only been off for 10 minutes).

So, my question is this: Why are the fans acting so erratically? I was under the assumption that the a/c being on should trigger both fans to run. Is this a relay problem? I've seen both fans run, so I wouldn't think that the sub-fan motor is broken, but I'm not sure. All fuses are in tact. I didn't test the main fan relay, but maybe this is the culprit?

Any help would be much appreciated.
 

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According to the wiring diagram, both fans should be on at the same time. What is controlled is their speed -- either slow or fast (two speeds only). For slow speed, a set of three relays connects the two motors in series between the 12 V supply and ground. For high speed, each motor is individually connected between the 12 V supply and ground.

The fan motor speed selection is done by the engine control module, based on engine coolant temperature, vehicle speed, and whether the AC compressor is presenting a low or high load on the engine.

I read through each of your observations, but because not all of the parameters are available, it's hard to come down to a single probable cause.

There have been reports here of fan motor failures, so it's not impossible that you're experiencing the early signs. Then again, it could be a faulty relay.

All three relays are accessible in the engine compartment fuse panel and could be removed for individual testing of the contacts. (I'm reluctant to suggest just replacing them with new ones as this might turn out to be unnecessary, but if it's simpler for you to eliminate them that might be a way to go.)

The fan motors have brushes. Sometimes when they're worn out or contaminated, the motor won't start depending on the position where it last stopped. So it might not start up the first time, but after driving (the air will cause the fan to turn a bit) it will start turning when power is applied.

Thus the dilemma -- determining if the problem is in a fan motor or a relay.

If you can test the relays, I'd suggest starting with the sub-fan relay and the main fan relay #2, as these are in the sub fan circuit in all cases. The main fan relay only connects power to the main fan when high speed is required, and based on your descriptions, it appears as if the main fan is the one that is working consistently.

Do some searching here -- there have been related threads, and at least one I can recall links to a video on testing relays. I also have some info in my AC thread: http://www.subaruoutback.org/forums...essor-poor-ac-performance-check-ac-relay.html. Note, the sub-fan relay and the main fan relay #1 are SPST, the main fan relay #2 is SPDT.

Some ideas -- hope this helps. Let us know . . .
 
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