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00'RS/02' WRX stgEleventy
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Discussion Starter #1
Hey all,

I know im one answering things a lot.. I need some help myself this time..

Ive got an 02 forester as my DD (essentially my RS in every way).. the motors recently been changed for a fresh rebuild.. new thermo and well burped..

It seems it doesnt matter outside temp if I run the defroster the AC cooling fan runs pretty constant.. and even when im NOT running the defroster the cooling fan seems to come on quite a lot.. we havent been over 30* in a while yet the fans run a lot.. I also disabled the AC recently (pulled the belt) as it wasnt working well.. do I need to unplug the AC pump electrically?

I know the main temp sensor could be wonky on the crossover pipe.. but what about the AC fan..

Thoughts?

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2000 2.5RS/C BRP
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When the defroster is turned on, the AC is supposed to turn on. I know on older cars turning on the AC simply forced the secondary fan on, though I believe that changed. IIRC, both fans are now controlled by the ECU, so for whatever reason it thinks you need both fans...
 

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00'RS/02' WRX stgEleventy
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Discussion Starter #3
I know this thanks... im trying to figure out why it seems excessive to me..
Even with the AC off the regular cooling fan cycles a lot.. it was 10* the other day and I herd it come on at a light..

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00'RS/02' WRX stgEleventy
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Discussion Starter #5 (Edited)
Come on man.. you should know me better...

New stock factory thermostat used.. alas I did not mention that in the OP.. my mistake Sir.. im usually better but its been a long week

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2000 2.5RS/C BRP
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Presumably you have an OBD2 scanner, have you looked to see what the ECU reports the temp as?
 

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00'RS/02' WRX stgEleventy
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Discussion Starter #7
I have a code reader but not a scanner.. a friend of mine however does.. just got to see it used..

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2000 2.5RS/C BRP
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I'm thinking the ECU's sensor is bad, since the dash sensor is a different part, the gauge can read happy but the ECU can think it's hot. Hence you read the current temp with the scanner.
 

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'MURRICA!
Hybrid Camry
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On the 02's the dash sensor is integrated into the ECU sensor. Same part, but 2 different outputs. Could be worth a try, as it's a pretty cheap/easy part to replace.
 

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00'RS/02' WRX stgEleventy
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Discussion Starter #10
I'm thinking the ECU's sensor is bad, since the dash sensor is a different part, the gauge can read happy but the ECU can think it's hot. Hence you read the current temp with the scanner.
ECU sensor?

Dash sensor?

Im on the same road but not following close enough.. hahaha

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00'RS/02' WRX stgEleventy
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Discussion Starter #11
On the 02's the dash sensor is integrated into the ECU sensor. Same part, but 2 different outputs. Could be worth a try, as it's a pretty cheap/easy part to replace.
See above and explain thyself pleaee..


Thank you Sir!

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'MURRICA!
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There are 2 different signals that the "Temp Sensor" sends. One, goes to the cluster to display the temp gague. The other goes to the ECU.

These signals are COMPLETELY different. You can't substitute one for the other.

So it's entirely possible, if your temp sensor goes bad, for it to "Display" correctly on the cluster, but it'll be sending the wrong signal to the ECU.

Or vice versa. But usually it's the ECU that gets sent the wrong signal.

Now, there used to be 2 different senders, located right next to eachother. One for the cluster, one for the ECU. Then subaru changed over to a 3-wire sensor which combined them.

Which is why he asked if you had checked the ECU to see what temperature it was showing, because it may be different than what the cluster is showing (Because they're 2 different signals).
 

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Mis-speak on my part, I did mean it was the same sensor but two different "circuits". BRZCory covered the rest of the explanation pretty well.

Interesting tidbit to add, though- when Subaru switched to the 3-wire ECT sensor, they kept the dash sensor for a little while anyway... One of my 251's had both, both were wired in.
 

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2001 Impreza GT
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738 Posts
my wagon dd does the same thing. if defrost is on there's a connection in there that turns your ac on and then your radiator fans on. no matter what temp. i even pulled my ac compressor relay out so i can run defrost and not lose what little hp the wagon makes running the ac.
o.e thermostat, engine temp is always below 195 (its been 10 degrees outside)
 
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