Scooby Air Con

How does the Subaru ECU 'know' if Air Con is fitted?
I'm still having problems with fan operation - comes on at around 85° and I'm wondering if my doner had air con and needs to be fooled into thinking it hasn't.
eg if one of the ECU wires needs to be grounded, 12V highed or shorted.

Cheers

Hi,

Nope..

The ECU gets a positive signal from the a/c switch when you turn it on. It actually pics it up near the a/c compressor with the trigger wire for the electric clutch. The ECU then ups the idle.

You say your fan comes on at 85 deg, what are you mearuring this with ? It isn't that far off where it usually comes on.

What model is it ? Some have a twin fan trigger with the 2 stage fans taking two different trigger temps. You could have the low temp wire,

Hi Brad

It's a 97-98, SOHC, NA EJ20 - the style of valve covers is the shaped version, not the big flat square one. (Screw and nut valve adjusters)

The motor was shipped with the correct main loom and ECU, but I was supplied the front harness from a turbo with aircon, both twin speed fans, grrr.

The temp has been taken using a Fluke Thermocouple sensor on the main water manifold to check my VDO 40-120° Gauge and sensor.

The main fan is meant to come on at 95C if driven under 69kmh (43mph). The tables show that the Aircon fan will turn this on at a lower temp/speed if the aircon is on. (Edit: Hence my thinking)
There's the Non-Aircon one in Pete's "Best place for rad" thread page 2. (Now you've eliminated that)
I do have a 4 pulse per wheel rev fitted although this will muck up the speed calc due to rolling dia differences. I needed one as the ECU threw a hissy fit ie cut IGN on cruising.

My fan seems to be on all the time the engine is over 85 which isn't right

Are you suggesting I've used the Air-con trigger for my main fan? (This is one thing I have been pondering also, just trying to eliminate things. Nothing I have been able to find tells me what temp this switches at)

Does the "Test Mode" (Green plug connected, black disconnected) cycle the Air con fan (if fitted) too?

I couldn't find any wiring diagrams that matched my ECU & had to buzz the lot out. Having the wrong front loom may have gashed up the traces to the fans!

I hope to have it sorted this weekend. A few 12V LEDs connected to the ECU for tests if all else fails.

Thanks for taking the time to answer & ruling out 1 option 🙂

I'm the sort of person who doesn't like 'work arounds" ie fixes not cures.

[ Edited on 10-5-2007 by ElusiveStranger ]

Bad form to reply to myself but...
Looked again, looks like mine should have been a twin fan (both single speed) set up.

I think I have wired the sub fan control to the relay not the main fan. D'oh.

My fan's around 18" dia and is 30A draw, single speed. Should I think about:
1/ wire this as main
2/ two smaller fans - single speed
3/ Big fan - twin speed

As an aside I have found out that the Subaru temp gauges are "dead" around the 70-100C mark. (Cite http://bbs.scoobynet.com/general-technical-10/592402-water-temp-gauge-sensor.html)
That's how come every Scooby owner I've spoken to says "My needle doesn't move, the temperature's stable"
What the eye doesn't see etc *grin*

Cheers guys

On my 96 model, if the ECU wanted to turn the fans on (over 85deg) it would turn them both on. If the air con was on (pressure healthy, evaporator healthy and compress on, it would switch only the sub fan on, if the fans wern't on already. Another thing i found was that each fan ran off different fuses. The test connector should turn the fan on and off every few seconds. Have you tried the haynes manual for the schematics? That was my best match.
If your still having dramas, maybe you could ditch the subaru setup and put in your own themoswitches (and relays) to turn the fans on, you could get two at slightly different temps as well so you don't have two fans running together all the time.

Whoohoo (I think)

I had used the low temp trigger (sub fan).

Now wired up to the Main Fan trigger. Added a couple of "Fan Trigger" LEDs (although no fan connected to Sub Fan relay) & took her out for a blast.
Approx 40 miles, ragging her where I could, including two long drag hills.
Didn't get over 85° cos it's lashing it down in good Ol Blighty.

Ratbug - I couldn't find any schematics that matched. I tried BIG time, hence having to buzz out the whole ECU.
I think my engine (NA) didn't have Air Con fitted. But the breakers supplied me with the front loom & fans (both twin speed) from a Turbo with AC fitted. That's what's thrown me I think.

Thanks for the replies guys

Happy Days 🙂