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R32 - Have Your Overheat Fan Turn On With Your A/c


Cubes

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Hey ppls,

The R32's (unsure about R33 or R34's) have an engine overheat fan positioned on the aircons condensor.

The engine over heat fan ONLY turns on when the water temperature reaches ~92-94degree's. The temp sender switch is located in the bottom tank driver side of the radiator.

This overheat fan does NOT turn on when you hit the A/C button.

Having the engine overheat fan turn on with the A/C allows air to pass over your aircon condensor when stationary, this improves the aircons efficiency/coolness and reduces engine temps (at the very least slows the increase in temp when sitting in traffic). This is especially critical if you have had your aircon converted to the R134a gas.

The R134a gas is not as efficient as the old R12; it runs a much higher head pressure, places a greater load on your compressor and places a greater heat load on your condensor.

Forcing your overheat fan on with R134A when the a/c is in operation WILL improve your aircon's coolness during long periods of idle or very slow speeds.

Most Aussy released cars automatically have the 'engine overheat' fan enable when you hit the a/c button.

Its required for our hot climate during heavy traffic.

Having my aircon recently serviced I decided to do something about having the engine overheat fan turn on when I hit the A/C button.

I remembered the A/C and Engine Fan relays were situated next to each other in the fuse/relay box under the bonnet.

See below pic.

post-382-1169695812.jpg

I grabbed the multimeter and found the trigger on both relays which happens to be the far left wire on both relays. Do note the wiring is negative switching; the relay see's a constant battery voltage, only when the relay is earthed does it activate.

Please do check yours to ensure you have the right trigger wires.

Mine were:

A/C - Green wire Yellow stripe

Overheat Fan - Green wire Black stripe

See below pic.

post-382-1169695821.jpg

I bridged the wires and presto... The engine fan turns on with the a/c. BUT the problem here is the a/c now also turns on with the engine over heat fan when the engine overheats (~92-94degree's). See below pic.

post-382-1169695796.jpg

The solution to having the a/c turn on when the engine overheats is to use a SINGLE DIODE!

As the relays activate when earthed place the diode appropriately. See below pic.

post-382-1169695829.jpg

So its as simple as that. Head down to Jaycar, grab a meaty diode (~0.25c) and splice it in to the trigger wires.

post-382-1169695836.jpg

Be bugged wiring in another relay; this is a cheap very tidy solution.

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Good one! So the diode (one-way only) stops the A/C from seeing the fans ground? But the fan can see the A/C's ground, so it comes on.

I was keen to do something like this!

Oh, and to confirm, my 33 doesn't switch the fan on when the A/C is on either.

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All done. :D

I ended up using a little wire to position the diode away from the loom so to speak.

There's just not enough room in there.

A flux pen gives very very tidy solders as it literally sucks the solder off the iron and evenly spreads it.

I have solder with a flux core but there's just nothing like having flux on the item that you are going to solder.

I first covered the joins etc with liquid elec tape. Why? Because I had some laying around, liquid elec tape tends to go soft with heat. So its not that crash hot but does keep water out.

post-382-1169712146.jpg

And now all taped up.

post-382-1169712155.jpg

You can only just see a little bit of the white wire under the relays. :no:

post-382-1169711988.jpg

Stoked I didn't have to bugger arse running another relay and chopping in to wires that really wasn't required.

Remember your all smart individuals, its up to yourself to perform your own research and decide IF you should attempt this mod. I'm not going to be responsible for you breaking something. :yes:

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I have been thinking the same thing Cubes, and the same issues (S2 97' GTST) Has anyone worked out yet what relay/pins the R33 fan runs off? I was just going to splice in my own relay/find a spare and have a switch to manually turn the fan on.

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Chris,

If you have both the A/C and Rad/Blower Fan relay on your fuse/relay box then you will be able to perform this mod. :yes:

Have a read up on automotive relays, from what I've read automotive relays are usually negative switching.

It really is easy, have a play with a multimeter for a while, you can't short or blow anything up testing with a multimeter so fear not. :D

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  • 2 weeks later...

I'm planning on hooking my thermo fan up to this, so I tested the on/off temps last night (via CONSULT), so for the record on my R32:

*** The fan switches on at 91C with a 3C hysteresis (i.e. off again at 88C). ***

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  • 2 weeks later...

When you say it "stays on", you mean after you turn the AC off, yes?

The std Ran fan is attached to the engine, so it's obviously, always on.

As for the AC one, remember it's an overheat fan, so your car could be running at 91+C and triggering the fan that way.

But don't be scared by the word "overheat", 91C is fine (your temp needle in the instrument cluster doesn't hit "Hot" until closer to 110C), it's just used to help out the clutch fan in hot weather etc.

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Easy way to find out.

Hit the a/c button and the fan should 'instantly turn on.

If its cycling in and out when the a/c isn't then check engine temps and you may very well find that is whats activating the engine overheat fan.

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Yes.. Run a wire from the rad fan relay in to the cabin, in to a switch and then earthed. (remember the relays are negatively triggered)

But why would you want to do that?

Just have it activate when you hit the a/c switch like aussy cars do.

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