Adker

Pin 2 has a ref to location K49. So you go looking at K49 for a wire from B22. And the winner is it goes to a switch (term W) in the water temp sensor. The manuals talks about this switch as a reason the AC clutch will not turn on. This relay works backwards from the way one looks at it at first glance, at least it did to me. When it turns on, it stops the voltage from getting to the AC clutch. The relay will turn on when the temp switch closes which opens the contacts going to the AC clutch.

So, I am guessing it is a safety to prevent the car from overheating due to the the load of the AC with the engine under a high load. I have heard of this occurring on long grades at high altitude.

For your application, just ground pin 2 of the AC relay and the AC clutch will turn off.

Pauerman

Awesome Adker!!

This is the conclusion I was leaning towards - controlling pin 2 at G17 realy.

I am planning on removing the factory pin 2 wire from the G17 and replacing it with my new ECU ground trigger wire. Do you think that the factory pin 2 wire should be removed from the relay or will tapping into the wire be sufficient? I am concerned about what will happen to the other instruments or sensors that are tied into this wire if I splice into it and apply a ground.

Tom M'Guinn

An arduino could do it for $20 or less

Pauerman

Tom, this may be a worthwhile mod.

I've neglected to hook my personal car up this way and I've snapped the A/C / alternator belt coming on to boost with hard the A/C on.

Tom M'Guinn

I'm on the road for a week or so but could work something up when I get back. Should be a snap. Any idea how much current the clutch draws? Zeitronix sells their TCAC (throttle controlled a/c) for $55, though it's made for Mitsubishi's so not sure if it would wire in directly. With the arduino, you could trigger based on whatever inputs/combos you want.

Adker

You can remove the wire coming from the temp switch and going to pin 2 of the relay. It is normally open so I can't see any reason you couldn't remove it and nothing else is tied to this wire. There are two wires coming from the temp switch, one is a gauge and the other is a switch. Might want to keep the gauge. If you tap into it, you still have the temp switch as a backup against overheating which is not a bad thing to have. The wire goes in and out of the central electric box so if you are gutting it, it might not be connected anymore.

Adker

If you put a hobbs switch on this wire, any 944 could shut off the AC at low boost. You can get to one end at the temp switch with little trouble to connect up the hobbs. One side of the hobbs switch connects to ground, the other to the wire on the temp switch.
http://www.partdeal.com/stewart-warn...nal-76576.html

JJR512

On previous cars I've owned (which have been more modern than any 944), the AC clutch would be disengaged at WOT. I suppose the reason was to make all engine power available for acceleration, which is presumably what you want if you're going to WOT.

It sounds like the 944 does not do this, from the answers provided in this thread so far.