1G 1g AC not working

[Mischif]

92 GSX Trying to get the AC system to work but it wont turn on.

When I press the button neither the orange or green light will come on and I get no power to the AC clutch. The driver side fan will turn on however when ever the ac button is on. At the AC relay in the engine bay I've confirmed it gets constant power, has ground and there is continuity from the out pin to the compressor clutch wire. But there is no power at all at the signal pin.

I've confirmed the wiring from ECU pin 7 AC switch is good and wiring from the ECU AC relay (signal) pin 65 is good.

I've replaced the AC control unit with another and it made no difference. Ohm'd both temp sensors in the evaporator and they read the exact same as a spare unit I have laying around. So I'm lost as what to check now.

How does the AC button communicate with the ECU to tell it to turn on the signal for the compressor? Does anyone have a pinout for the AC button or know how to go about testing it?

 

[steve]

The FSM has quite a bit on the AC. I'll copy a bit of it in case you don't have it and for others to refer to.

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Note that test 4 is measure the pressure and test the pressure switch. Have you done this?

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As you can see the AC switch tells the AC Control Unit you want to cool and it then decides if it's OK to tell the ECU to cool, and then the ECU decides if it's conditions make it OK to turn of the compressor, and if so, pulls the relay coil low to engage the clutch.

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Not clear here but I assume there are two lights in the indicator (orange and green) sharing pin 5 to ground, pin 1 is Power, pin 4 is cool (shared between AC and Economy) and pin 2 is !Economy (not economy).

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[Mischif]

The car was a shell when I got it and the AC components In the engine bay were gone. I had to piece it all back together. Replaced all the black orings with green ones and vacuumed the system. I haven't refilled the system yet so there is no pressure in it, I wanted to verify everything works before I recharge it. I did bypass both the dual pressure switch and coolant temp switch so I could test and make sure I was getting 12v at the clutch connector. However it reads zero volts regardless of the AC button position.

When I tested the air inlet sensor and thermostat sensor they were both around .92 but the ambient temp was probably around 95 degrees. I guess I could wait till night time when it'll be closer to 77 degrees.

Hopefully with the switch test and control unit test you posted ill be able to pinpoint the issue. Couldn't find those anywhere.

That last step on page 24-5 about the engine idleing up after switch is turned on....well i deleted my iacv so the connector isn't connected to anything. Could that cause the AC to not turn on?

 

[AWD-Tony]

@Mischif what freon are you planning to use, r12A?

 

[1990TSIAWDTALON]

Run a jumper "test" wire from the battery + over to the "hard to get to" compressor and give the clutch connector a short 12v touch to see if will engage. That will tell you "something". If it does engage, then you have a break somewhere in the command wire or it's components. If it doesn't do a thing, then the clutch is either not grounded or it isn't working.
This is just a test.

 

[Red Rider]

This is just a test.

If this had been a real emergency, you would have been instructed on how to lower your heart rate from the accidental grounding of the exposed hot wire, and told where the beer was.

I'll also add

With the engine not running you should hear the clutch clack on.
With the engine running, with gauges on you can see if the compressor works.
Just because the clutch engages doesn't mean the compressor works. Or that the lip shaft seal is good.

 

[1990TSIAWDTALON]

I'll take "click and the engine off for $100 Alex" (Trebeck RIP).......as long as it isn't the sound of a safety on a gun behind me being taken off ( @Widgmaster) .........
With the engine off, it will be much easier to do a diagnosis unless you get to the point of seeing if it will produce cold air.

 

[Red Rider]

If I remember correctly, the front face plate on the compressor does not rotate when the clutch is off. So to verify the clutch works above the "Clack" when not rotating, when the drive belt is rotating (could be cranking, not running) when energized the front faceplate should rotate. With the clutch off, just the outer ring when driven by the belt will rotate. I haven't had it happen, but it seems possible the clack could be heard but does not engage enough to drive the compressor.

 

[steve]

That last step on page 24-5 about the engine idleing up after switch is turned on....well i deleted my iacv so the connector isn't connected to anything. Could that cause the AC to not turn on?

Not usually. I'm sure there have been many people driving around with an inactive ISC and the AC running based on posts I remember.

You said that the drivers side condenser fan runs when you activate the AC switch. Have you probed ECU pin 7 to see if the ECU is getting the signal to turn on the clutch?
If you ground ECU pin 65 does the clutch engage?

Given all the stuff you swapped maybe this is an ECU problem.

 

[Mischif]

You said that the drivers side condenser fan runs when you activate the AC switch. Have you probed ECU pin 7 to see if the ECU is getting the signal to turn on the clutch?
If you ground ECU pin 65 does the clutch engage?

Given all the stuff you swapped maybe this is an ECU problem.

From my understanding at pin 7 i should be probing for ground correct since that is for the dual pressure and temp switch. And pin 65 is a + voltage output isnt it, so grounding that would be bad.

I originally had a na ecu in the car and the ac button didn't work with that one either. Now it has the correct turbo ecu in it. So i hope its not an ecu issue.

Didn't get a chance to do any further testing on it yesterday. I plan on messing around with it some more today once i get home.

 

[steve]

You want to be measuring the voltages that exist first. That's what I mean by probing.

ECU pin 7 is sensing if the AC Control Unit is supplying voltage (either +5v or +12v, likely battery voltage) that is making it pas the pressure switch and temp switch interlocks.

ECU Pin 65 is the control line for the clutch but it works by pulling it's side of the clutch relay coil to ground. Since the other side of the clutch relay coil is connected to the voltage at the pressure switch, if things are good there the relay should be activated feeding power from Dedicated Fuse 4 to the compressor clutch.

At least that's what the wiring diagram is telling me.

 

[Mischif]

You want to be measuring the voltages that exist first. That's what I mean by probing.

ECU pin 7 is sensing if the AC Control Unit is supplying voltage (either +5v or +12v, likely battery voltage) that is making it pas the pressure switch and temp switch interlocks.

ECU Pin 65 is the control line for the clutch but it works by pulling it's side of the clutch relay coil to ground. Since the other side of the clutch relay coil is connected to the voltage at the pressure switch, if things are good there the relay should be activated feeding power from Dedicated Fuse 4 to the compressor clutch.

At least that's what the wiring diagram is telling me

The harness for the AC control unit tested fine, and I got the AC button working ( connector is loose) and that tested fine. But the clutch relay still won't do anything. Tested the relay and its good. Pin 7 and pin 65 of the ecu both show 0 volts with the AC switch on or off.

So what I'm understanding is the AC control unit(accu) sends out a signal from pin 4 When all conditions are meet and then goes through the dual pressure and temp switch into pin 7 of the ecu and then the ecu sends out a signal from pin 65 to the clutch relay. So is pin 4 of the accu supposed to be putting out battery voltage through the dual pressure and coolant temp switches into ecu pin 7? And pin 65 should change from battery voltage or zero volts to a ground?

I removed the wire from pin 4 of the accu and tested the pin on the accu directly. With the AC switch off it reads zero volts. With the AC button on It puts out a little over 3 volts unless I unplug either the in let or outlet air sensors( or both) and then it'll put out battery voltage.... But even like that when I plug the wire back to pin 4 of the accu I don't get a voltage reading at all at pin 7 of the ecu and neither the dual pressure or coolant temp switch read voltage, they just act as grounds. I also tested for continuity from pin 4 on the accu harness to pin 7 of the ecu harness and it has continuity.

I want to say that I potentially have bad inlet/outlet air sensors on the evaporator as well as a possible short somewhere between pin 4 of the accu and pin 7 of the ecu. But without knowing for sure what the output on pin 4 should be I can't really be certain.

 

[steve]

The harness for the AC control unit tested fine, and I got the AC button working ( connector is loose) and that tested fine. But the clutch relay still won't do anything. Tested the relay and its good. Pin 7 and pin 65 of the ecu both show 0 volts with the AC switch on or off.

So what I'm understanding is the AC control unit(accu) sends out a signal from pin 4 When all conditions are meet and then goes through the dual pressure and temp switch into pin 7 of the ecu and then the ecu sends out a signal from pin 65 to the clutch relay. So is pin 4 of the accu supposed to be putting out battery voltage through the dual pressure and coolant temp switches into ecu pin 7? And pin 65 should change from battery voltage or zero volts to a ground?

What I'm seeing in the diagram is that happens @ pin 1 of the ACCU C40 not pin 4. Pin 4 is the voltage source for the Air Inlet Sensor just like pin 8 for for the Air Thermo Sensor.

I removed the wire from pin 4 of the accu and tested the pin on the accu directly. With the AC switch off it reads zero volts. With the AC button on It puts out a little over 3 volts unless I unplug either the in let or outlet air sensors( or both) and then it'll put out battery voltage.... But even like that when I plug the wire back to pin 4 of the accu I don't get a voltage reading at all at pin 7 of the ecu and neither the dual pressure or coolant temp switch read voltage, they just act as grounds. I also tested for continuity from pin 4 on the accu harness to pin 7 of the ecu harness and it has continuity.

Continuity from pin 4 on the ACCU to pin 7 of the ECU would be a problem. They are not connected

I want to say that I potentially have bad inlet/outlet air sensors on the evaporator as well as a possible short somewhere between pin 4 of the accu and pin 7 of the ecu. But without knowing for sure what the output on pin 4 should be I can't really be certain.

 

[Mischif]

One diagram had the accu output pin labeled as 4 and the other had it as 1. So the output is a GW wire.

So i think i have 2 issues. 2 bad accu's and 2 ecu's with pins 65 being dead( whats the chances of that?)

If i jump the GW output wire from the accu to battery voltage while also jumping the RB pin 65 wire for the ecu to ground then my clutch relay will engage. So it seems pin 65 is dead and the accu isn't putting out the correct voltage from the output.

 

[1990TSIAWDTALON]

Lots of good information here. Thank you both!

 

[steve]

One diagram had the accu output pin labeled as 4 and the other had it as 1. So the output is a GW wire.

Got ya, I see it on the first overview diagram. Needless to say that one's wrong.

So i think i have 2 issues. 2 bad accu's and 2 ecu's with pins 65 being dead( whats the chances of that?)

Not very high I'd guess unless something is zapping them.

If i jump the GW output wire from the accu to battery voltage while also jumping the RB pin 65 wire for the ecu to ground then my clutch relay will engage. So it seems pin 65 is dead and the accu isn't putting out the correct voltage from the output.

Interesting, I wonder how we could check if the ECU is seeing the signal from the ACCU and trying to activate the clutch. I'll have to think about it.