A/C electricals

[E.T.]

Since the spring has come, I started fixing my non-working A/C issue which came with the car as bought it six months ago. PO said it was just empty, but to me it seems like there is some electrical problem.

It is a 94 v6 12v, european Super model.
While heating/ventilation works perfectly, the compressor is dead silent.Before I charge the system, I want to make sure the compressor clutch and all the electrics are operative, but I faced some mysteries to uncover.

Here's what i've verified to be ok so far:
-Control panel doesnt return errors and sends +12v to the "green" wire( mine is different color but it shoul make no difference) in red connector by trinary switch
-jumping black and brown wires in white connector switches on low speed fan
-Q22 a/c relay is good for sure
-I get +12v on Q22 relay pink wires
-there is connectivity between green/black wire at the compressor and the relay
-frost switch seems to be good ( has connectivity ) , though I bypassed it for the time of testing


I need some explanation on how exatly the trinary switch works.
As advised in other posts, to bypas the trinary switch some of you advise to jump the red connector's wires to check if Q22 relay clicks. I hear no click.
Is it the +12v, supplied to trinary switch by control panel, that needs to be supplied to the relay through the frost switch?? Or maybe the trinary switch behaves like a relay and after it receives voltage it grounds the Q22 relay to make it click.

The point that I am stuck at the moment is that I get no connectivity between the frost switch and pin 85 of Q22 relay. Sholud there be any?
I am confused, because my car has slightly different wiring than 91-93 cardisc shows. A mystery for me is that pin 85 of Q22 relay is green wire, and to frost switch comes grey/yellow wire( the problem is not that they are both different than 91-93 diagram, but that they are differentfrom each other at the "ends" of circuit).
I don't own a proper cardisc CD, can anyone verify if there should be connectivity between them and, once again, should there be ground or +12v applied to grey/black wire at the red connector by the trinary switch?

Not beeing sure, I applied groud to pin 85 of the Q22 relay throu a jumper cable and ... relay clicked and correctly applied +12v to the green/ black wire at the compressor ( key set to "on" position).So why do I need +12v from control panel at the trinary switch?

Best for me would be if someone explained precisely what energises what and what grounds what in this bunch of wires and connectors, possibly on a 94 car, but an earlier model description would be of great advantage for me too.

thanks for help
E.T.

[Alfisto Steve]

Quote:

Originally Posted by E.T. Since the spring has come, I started fixing my non-working A/C issue which came with the car as bought it six months ago. PO said it was just empty, but to me it seems like there is some electrical problem. It is a 94 v6 12v, european Super model. While heating/ventilation works perfectly, the compressor is dead silent.Before I charge the system, I want to make sure the compressor clutch and all the electrics are operative, but I faced some mysteries to uncover. Here's what i've verified to be ok so far: -Control panel doesnt return errors and sends +12v to the "green" wire( mine is different color but it shoul make no difference) in red connector by trinary switch -jumping black and brown wires in white connector switches on low speed fan -Q22 a/c relay is good for sure -I get +12v on Q22 relay pink wires -there is connectivity between green/black wire at the compressor and the relay -frost switch seems to be good ( has connectivity ) , though I bypassed it for the time of testing I need some explanation on how exatly the trinary switch works. As advised in other posts, to bypas the trinary switch some of you advise to jump the red connector's wires to check if Q22 relay clicks. I hear no click. Is it the +12v, supplied to trinary switch by control panel, that needs to be supplied to the relay through the frost switch?? Or maybe the trinary switch behaves like a relay and after it receives voltage it grounds the Q22 relay to make it click. The point that I am stuck at the moment is that I get no connectivity between the frost switch and pin 85 of Q22 relay. Sholud there be any? I am confused, because my car has slightly different wiring than 91-93 cardisc shows. A mystery for me is that pin 85 of Q22 relay is green wire, and to frost switch comes grey/yellow wire( the problem is not that they are both different than 91-93 diagram, but that they are differentfrom each other at the "ends" of circuit). I don't own a proper cardisc CD, can anyone verify if there should be connectivity between them and, once again, should there be ground or +12v applied to grey/black wire at the red connector by the trinary switch? Not beeing sure, I applied groud to pin 85 of the Q22 relay throu a jumper cable and ... relay clicked and correctly applied +12v to the green/ black wire at the compressor ( key set to "on" position).So why do I need +12v from control panel at the trinary switch? Best for me would be if someone explained precisely what energises what and what grounds what in this bunch of wires and connectors, possibly on a 94 car, but an earlier model description would be of great advantage for me too. thanks for help E.T.

[E.T.]

I and my father, who is an electronics engeneer, did some investigating on the diagraqms and it looks like ECU needs +12v from both A/C panel and the trinary switch to apply ground to pin 85 of Q22 ralay. In that case grounding the grey/black wire won't work. I start to suspect that everything could be ok and the only reason of innoperative A/C is that I am low on pressure in the system. The problem is that when I was checking the circuits the engine was off ( only the key turned) Now when I know it goes through ECU, I suspect that it doesn't aply ground to relay because it "knows" the engine is not running.
I plan to try jumping wires at the red connector by trinary switch but on running engine, hope it works, will post an update.

BTW,does anyone know where to look for G337 if I need to check if wires ok?

Thank you Steve for your help
E.T.

[goats]

The very first step in AC troubleshooting of any type, for me, i s to take pressures and temperatures. Even if no compressor engagement take the static pressure.

[Alfisto Steve]

Quote:

Originally Posted by goats The very first step in AC troubleshooting of any type, for me, i s to take pressures and temperatures. Even if no compressor engagement take the static pressure.

[E.T.]

It all works

As I planned, I started the engine and then jumped grey/black and brown/green wires at red connector by trinary switch. As I cycled the econ button on and off I heard the relay finally click.

I think it works like that : After switching a/c on, a/c panel sends +12v to Engine ECU .The same current splits into the grey/black wire and goes to trinary switch pin1. If pressure ok, it sends current further to frost switch which,if no frost on pipes, sends it to ECU ( frost/sw->grey yellow->g337 pin C -> pin 85 of ECU.

The engine ECU is the only possible source of ground which has to be applied to pin 85 of A/C Q22 relay to finaly energise compressor. Once ECU gets +12 directly from A/C panel through brown green wire at ECU pin B, it waits for +12 which comes from this additional circuit consisting of trinary switch and frost switch to ECU pin 85-this happens when proper pressure and frost conditions are met. Only then - with +12 on pins 85 and 86 of ECU ,somehow inside the ground is applied to its pin 48 straight to pin 85 of Q22 relay which energises compressor. Applying ground to grey/black wire will do no good- it will only close circuit of A/C panel feeding +12v, but will not cause the engine ECU to apply ground to Q22 relay. There is one more essential condition: the engine has to be running, otherwise ECU will not apply try to energise compressor clutch,simply because it "knows" there is no such need.

I think in earlier models engine ECU didn't decide on anything, it only got informed about A/C beeing turned on through pin 87a of Q22 relay to increase idle, this is why it was possible to aply ground to the wires to check for relay clicking.

now next step for me is to charge A/C and check it for leaks,

Thank you once again for help, I wouldn't have figured it out without your input.
E.T.