Aac Valve Not Getting Power!

[sirjb]

Hey guys I have an R34 GTT and when I turn on my aircon my revs drop massively, causing my car to stall at lights and such. I disconnected the AAC Valve and connected it directly to 12v with the aircon on and the revs will jump up to 1200 from ~550rpm. Which is where it should be sitting. I have checked at the ECU and it doesn't have any power coming out to the AAC. Even though with the scan tool it says AAC at ~100%.

The car has some weird rev drop when I start the car even if the aircon is off.

Any ideas would be appreciated!

[GTSBoy]

Sounds like the output is dead. Might have been accidentally shorted in the past by someone electrically clumsy.

[sirjb]

tried changing Ecu's. Which made no difference. Also tried changing aircon control units.

[GTSBoy]

OK, so where have you "checked at the ECU"? Right on the back of the plug? Got a decent probe that will actually reach in there properly? Air-con control unit is not responsible for idle-up on R34 like it was on some R33s.

[kitto]

Check for 12V at the AAC plug. Should have constant 12V on one pin with the ignition switch on. ECU controls the ground for the AAC using a PWM output when the engine is running

AAC valve itself could be faulty.

[sirjb]

WIN! So it should have a constant 12v? Which is what it is currently missing. Any idea where it comes from?

[sirjb]

After looking at the wiring diagram if the AAC doesn't have power, the Canister purge control valve, variable air intake control solenoid valve, turbo pressure control valve and air jet swirl control valve shouldn't have power either?

The AAC Valve itself is fine. I tested it by running 12v directly to it and the revs picked up drasticaly.

For some odd reason when ignition is on it has 1.4v once the engine is running with A/C on it has 0.01V????? What is going on here!

Edited February 6, 2013 by sirjb

[kitto]

After looking at the wiring diagram if the AAC doesn't have power, the Canister purge control valve, variable air intake control solenoid valve, turbo pressure control valve and air jet swirl control valve shouldn't have power either.

Correct, but if its just the part of the loom that controls the AAC valve that is damaged then only the AAC valve won't work.

I'm not sure if that circuit is powered from a dedicated fuse? Quite possible 'Engine Control' Fuse at 10A? I'm not familiar with the body loom of an R34, only the engine side of things.

02 Sensor won't have power either, the air jet swirl valve and variable intake control valve would only be on DE's i would say.

[sirjb]

So I got a good multimeter from work and did some testing. When the ignition is switched to 'on' with the engine off, there is 12v to the valve, but there is no ground continuity. Once the engine has been started the 12v disappears and the continuity of the ground is all good. SO for some reason the 12v is dropping out once the engine is running, any ideas?

Edited February 7, 2013 by sirjb

[sirjb]

If anyone else has this same problem it is due to a faulty fuse which lets some voltage through but as soon as there is some resistance it disappears. Hint.... Use a test light instead of a multimeter when testing fuses as it shows true voltage!

[kitto]

Ahhh i see. Tricky fuse huh.

Multi meter's are good you've just got to know what your looking for and how to diagnose issues in a step by step process.

Test lights are handy though.

[MrRx7s3]

Hey guys, Well it looks like my aac valve isn't working correctly or God knows what it is, I apply 12v to the solenoid and nothing changes, I also have a spare solenoid here and when I apply 12v to it nothing happens??? is it meant to move in and out or something? please let me know asap, thanks.

[89CAL]

Complete circuit (12 V source to solenoid to ground)?

pull the solenoid off the valve and have a look. You should feel it work if you hold it while applying and removing 12v, its only held on with 2 little screws

Because they work off frequency (PWM) you will not be able to do much more then see if it functions. It shouldnt matter which pin you apply 12V to, as long as it has a circuit to ground on the other pin.

[MrRx7s3]

Complete circuit (12 V source to solenoid to ground)?

pull the solenoid off the valve and have a look. You should feel it work if you hold it while applying and removing 12v, its only held on with 2 little screws

Because they work off frequency (PWM) you will not be able to do much more then see if it functions. It shouldnt matter which pin you apply 12V to, as long as it has a circuit to ground on the other pin.

Hey man thanks for the quick reply, yeah I apply a positive to 1 pin and 1 negative off my booster pack onto the pins and nothing happens and I can't feel it doing anything, or do I have to do it with the car power so that I can put a earth instead of negative if that makes any difference? thanks.

[89CAL]

Just make up something to go straight on your battery if you want to test it properly. Just be careful not to touch the wires together

[MrRx7s3]

So just off the battery positive and negative or should I get positive off the battery and earth off the car? thanks.

[MrRx7s3]

Also should I ground the actual solenoid eg. connect a wire from the ground to the solenoid body or is just the 2 pins ok.

[SiR_RB]

Just need positive and negative to terminals

[GTRsean]

I think mine has this issue too (34GTR).

Tested the solenoid and it works, so it's something on the car...

Either the ecu or wiring, have to do some troubleshooting I guess.