AC compressor problem

Have now been looking for why my compressor's magnet does not get any voltage when you turn the AC button. The relay gets voltage. When I ground pin (1) the magnet turns on. Does this mean the button is not working? or does anyone else have a better suggestion?

[mettersl]

I know this sounds obvious, but does the system have gas in it? If not, the pressure switch will prevent the system turning on.
Otherwise, can you post up a scan of the whole wiring diagram for the AC system, there isn't much shown there to go on and the wiring is different between Turbo and Atmo and also changes with model years.
I'd start with gas pressure, you can test this my shorting the pressure switch and seeing if the pump starts, but don't do it for long (a few seconds only) as the pump should not run without gas.

Thanks for the tip, but the car has new gas in it and passed the pressure test.
My wiring diagram for the 1990 model year looks to be correct.
Thanks for all help!!

[mettersl]

Thanks for the whole wiring diagram and confirming that its a 1990 Turbo.
The wire that you are grounding, as I am sure you know, is connected to the engine ECU. It's labelled on the ECU wiring diagram as the AC clutch disconnect.
Unfortunately, the longer description of the function of the AC related wires are missing from the descriptive table in the wiring books I have scanned so I can only guess that the ECU cuts the AC clutch when you floor the throttle to maximise performance. I have seen this on other car types.
If the connection wiring to the ECU pin is in good condition, it is possible that the ECU has some internal damage and this function no longer works, you should be able to check by measuring continuity to ground at the relay socket (with the relay out) with the engine running at idle and the AC turned on. A610 ECU can suffer from the same problem with the fuel pump control, so it must be possible for a car to work with some small ECU issues.
As the D500/Atmo has no equivalent high engine speed cut off function, it should be safe for the AC pump to work through the engine speed range, so I think you can ground this wire permanently without a risk of damage and get your AC working.

Still scratching my head trying to get this right.
The relay has voltage on the red from the battery. The yellow ones from the control button and to the ECU have constant voltage when the ignition is on, regardless of the control button are On or Off. No voltage from the relay to the magnet of the AC.

[mettersl]

Hi,

Does the power to the relay on the yellow wire from the ignition lock/adjustment panel go on and off with the AC on/off switch? To measure this take the relay out then with a DC volt meter attached to an earth point on one side and the relay socket pin to the switch on the other it should be 12-14v with the ignition and AC switch on and then nothing (or something tiny) when you turn the AC switch off- if so it's OK .

If it doesn't, then as this circuit goes through a lot of connectors, a wiring fault would not be a surprise. You will need to trace it back until it does turn on and off, and then work out where the fault is, until the pin on the relay goes on and off with the switch.
Aside of connector or wire damage, there seems to be an external temperature sender in that circuit too, that could be faulty.

However, if you get the power turning on and off, then you need to look at the other earth connection through the ECU. That can only be tested with the engine running. The circuit diagram says the ECU grounds the relay, to allow the ecu to turn off the AC at high revs to make acceleration quicker at high revs.
If that wire to the relay socket does not drop close to zero volts (against the earth) when the engine running, you then need to check the wiring from the ecu (pin 13 at the ecu) to the relay socket. if its good then there is damage inside the ECU. In that case I would disconnect the ECU to relay cable and run a permanent earth to that pin.
The Atmo does not have the pump cut off, so the pump should be fine on a turbo without the cut off too.
I'd offer to come and help, but I don't know where you are, also apologies if you have done all this already.
Lee

A big "thank you", Lee.
Will follow your instructions and hope to get closer to a solution.
However, I live in Sweden, but of course you are welcome here on a holiday, perhaps?
/Jörgen

[mettersl]

HI,
I hope it works...I like Sweden, but its been a while since I have been there- and its a very big country!
Good luck

Have now measured and observed a strange behavior. The power from the control (yellow) gives 11.1 V, constant when the ignition is switched on, Independent of the adjustment panel is "on" or "off" . Is this a sign of an error in the adjustment panel? The red from the battery has 12V.

Could the mystery be solved? The yellow ones have been joined together, maybe because the rheostat is broken? When I resoldered all the cables according to the scheme, the Japanese ugly repair didn't work anymore? Now looking for a new rheostat Item: 60 00 008 218. Tips are gratefully received. (Simon: item 061225 "out of stock")