Stagea Air Conditioning

[fmlycar]

I have recently purchased a 1997 s1 rs4 stagea. Car has been converted from auto to manual and is running a r34 power fc. Ran a sensor diagnostics and all ok. I have no power at the compressor or high pressure switch plug. Checked relay ok, fuse in eine bay ok. Is there anything else I should be checking? System has been pressure tested and is all ok. Gassed up and still no compressor running. Want to see if I can sort it myself before I resort to seeing an auto sparky.

[fmlycar]

Anyone?

[zoomzoom]

How did you check the relay?

If you tested the relay itself while removed from the fuse box, and its functioning correctly, probe the pins on the relay harness to earth and measure the voltage. With the relay coil, one side should supply 12v power, while the other side is earthed to the ECU when the ECU wants to switch on the compressor.

The power circuit on the relay should have 12v when the key is switched on, and the other side is earthed through the compressor.

Post up the results and that should narrow it down.

[zoomzoom]

Dont forget there is also a fuse in the drivers side coin tray area which supplies power to the relay coil, as well as a few other things like vct, o2 sensor, and idle.

[fmlycar]

Checked all the fuses behind the coin tray and they were ok except for 1 7.5amp which was second in from the right top row, however that didn't have any power at the pins (will check with multi meter tonight). As far as checking the relay, I swapped it out with a k own working one. Haven't bridged anything yet. Might rig up a fused test wire and try that.

[fmlycar]

Also checked sensor settings on the power fc and ac is functioning as it should

[fmlycar]

So the wire that goes to the compressor is only a earth?

[fmlycar]

Bridged the ac relay and compressor clicked on. What is left to check. System has 100 psi in it also. I'm thinking ecu related since it is a s1 stagea running a r34 gt-t ecu?

[zoomzoom]

So the wire that goes to the compressor is only a earth?

Yes, one side of the relay power circuit is powered by the battery when the key is in the on position. When the relay activates, the power is earthed through the compressor and it turns on the magnetic clutch. Since that worked manually it seems that circuit is fine.

The relay coil always receives 12v when the key is in the on position, then the ECU grounds that circuits when it wants to switch the A/C relay on.

That is the other main one to check. Have a look on top of the relay for a diagram of which one is the relay coil pins. Unplug the relay and ensure that one of the relay coil pins is reading battery voltage, otherwise that circuit probably has a blown fuse (or worse). The relay coil fuse will be the one I mentioned near the drivers knee compartment.

If you do have battery voltage to one side of the coil, try manually earthing the other side of the coil (with a little jumper wire or similar while the relay is plugged in). That should also activate the relay and turn on the A/C. If that is the case then the issue is closer to the ECU.

Edited February 20, 2015 by zoomzoom

[fmlycar]

It's looking like it is actually to do with the ecu side of things. Anyone know how to get a R34 gt-t ecu to control the ac in the stagea? The original ecu was apparently one of the rare one's, however I don't know how much of the loom has been changed to suit. Is there a way to get the R34 ecu to run my ac? Really like to get this working as it's 40+ every day atm.

[zoomzoom]

Pin 14 and 21 on your original loom plug should be all you need to work out. Assuming everything works, when the climate control wants to turn on the A/C, it sends a signal to pin 21 (cant remember if it grounds a 12v signal from the ECU, or actually supplies 12v to the ecu). Then if the ECU thinks all parameters are normal, ie not full throttle or overheating etc, it then grounds the A/C relay, turning it on.

So you just need to find those 2 pins on the power fc pinout and connect them to the correct wires on the loom, if they are in different positions to the stock ecu.

WGC34_Series_1___STAGEA_RB25DET_Auto_ECU_Pinout_translated.xls

[zoomzoom]

Do you have the number of your original ECU? Does it have 23740 0V300 on the sticker?

[fmlycar]

Standard ecu according to fast is 0V310 which I have found is rare. I don't have the original ecu to confirm though.

Although every pinout I have seen so far, those wires should be in the same position. However, some suggested that the stagea uses negative switching and the r34 uses positive. How can I get around that if that is the case?

Edited March 3, 2015 by fmlycar

[zoomzoom]

Ive been meaning to make something similar which would make a pull to ground switch into a 12v switch using a 2N3906 transistor, but is was for very rapid switching (a tacho)

In this case couldnt you invert the state by using a small relay? You'll need to be specific whether the AC relay, or the climate control is the affected one.

transistor.switches.pdf

[fmlycar]

How would I check which is the effected circuit?

[zoomzoom]

Have the car running.

Backprobe pin 14, then measure the voltage between that and earth.

Measure the voltage with the A/C switched off, then on.

Repeat process with pin 21.

Post up results.

Edited March 6, 2015 by zoomzoom

[fmlycar]

Back probed pin 14 and had no voltage. Pin 21 was 0v ac off and 12.5v approx ac on. Checking pin 14 and it switches ground from what I can tell. Checked continuity with ground on pin 14 and I applies ground when ac is switched on. So where does this leave me?

Edited November 8, 2015 by fmlycar

[verm69]

I'm running a R34 Gtt ecu and my AC isn't working either... A solution to this will be awesome!

[Dan_J]

mine stopped working as well, in the engine bay i found a random ignition source and replaced the ac relay trigger wire with that, sure the relay will always be open when the car is on, but ac will only work when u push the a/c button on climate control

[fmlycar]

I've tried bridging the ac relay in the engine bay and the compressor clicks but doesn't get cold. Suggestions? Is there another relay in the cabin near the fuses?

Edited November 20, 2015 by fmlycar