Resolved 92 Galant Air Conditioning sensor hunt

[sebas-1024]

Hi, I'm in the process of hunting down and properly testing and connecting all A/C sensors, if I'm not mistaken, that would be:
1. Air Inlet Sensor.
2. Air-thermo Sensor.
3. Air conditioning engine coolant temperature switch.
4. Engine coolant temperature switch.
5. Refrigerant temperature sensor.

1. The Air Inlet Sensor might actually be in the right spot as the wiring seems to be there, but I tried reading the resistance values and got nothing, which shouldn't be the case I believe. according to the diagram it has two yellow and blue wires. Any idea as to where a replacement could be found? Also, I was not confident enough to crack open the evaporator housing and see for myself if the sensor was there, is that Ok to do?

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2. This one was trickier, there was one end of the connector with the yellow and red wiring, but the only other wiring coming out of the evaporator was this "variable resistor"? Which I assume was used to trick the Auto Compressor Control Unit into thinking that the sensors we're giving the right resistance values, but honestly I can't really prove anything at this point.

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3 and 4. Neither of these 2 seem to be in the thermostat housing, which is where I understand they should go according to the manual, there is a "threaded Allen nut"? at the top of the housing which would seem to be where the Air conditioning engine coolant temperature switch should go, but don't see room for the Engine coolant temperature switch in my the thermostat housing.

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5. I think I actually have this one, it was plugged into the previous A/C compressor which is in the trunk of the car, didn't get a picture of the sensor but do have one of the compressor, which doesn't seem to be the right model for this car, it should be FX105V I believe.

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Even though some sensors seem to be there, does anybody know where I could purchase all of these, or if that's impossible maybe some generic sensors that work with the same values could do the trick and could be used? I'm not very experienced with electronics so I'm not sure what to look for besides what the manual says.

As always, sorry for the long post and thank you for your help.

 

[petrosian]

I can see one thing that's missing from your list of sensors/switches: the A/C dual pressure switch. Its in the front of the engine bay on the right side, part of the A/C refrigerant line. It prevents the compressor from running if refrigerant pressure is too low/high.

That thermostat housing looks like one from a SOHC engine. The housings came with those threaded plugs from the factory since the SOHC A/C system didn't use the "Air conditioning engine coolant temperature switch" (#3). You noticed the threaded plug screwed in where #3 would normally be. I'm attaching a schematic of the 91+ Non-turbo Galant A/C circuit with markings. Is there an unplugged wiring harness plug hanging in that area or evidence of modified wiring?

The "Engine coolant temperature switch" (#4) (not to be confused with the "Air conditioning Engine Coolant Temp Switch" or the "Engine Coolant Temperature Sensor"): According to the manual, this switch is only found in "Non-turbo AWD-Automatic" (Galant GSX) and Turbo Galants for 1992 (See diagram). So technically you aren't missing this one

I think RockAuto.com ships internationally--if you're trying to acquire the one sensor you are missing (#3)--but it looks like you should be able to get it going without that as long as the wiring is correct. I'd check out that dual pressure switch though. Hopefully your refrigerant charge is still good.

I read in one of your previous posts that you're located in Venezuela. Maybe the Galant models were slightly different there, like we've seen with other countries.

https://www.dsmtuners.com/threads/92-galant-diagnosing-a-hard-start-condition-and-random-low-revs-while-running.543845/

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[sebas-1024]

I can see one thing that's missing from your list of sensors/switches: the A/C dual pressure switch. Its in the front of the engine bay on the right side, part of the A/C refrigerant line. It prevents the compressor from running if refrigerant pressure is too low/high.

That thermostat housing looks like one from a SOHC engine. The housings came with those threaded plugs from the factory since the SOHC A/C system didn't use the "Air conditioning engine coolant temperature switch" (#3). You noticed the threaded plug screwed in where #3 would normally be. I'm attaching a schematic of the 91+ Non-turbo Galant A/C circuit with markings. Is there an unplugged wiring harness plug hanging in that area or evidence of modified wiring?

The "Engine coolant temperature switch" (#4) (not to be confused with the "Air conditioning Engine Coolant Temp Switch" or the "Engine Coolant Temperature Sensor"): According to the manual, this switch is only found in "Non-turbo AWD-Automatic" (Galant GSX) and Turbo Galants for 1992 (See diagram). So technically you aren't missing this one

I think RockAuto.com ships internationally--if you're trying to acquire the one sensor you are missing (#3)--but it looks like you should be able to get it going without that as long as the wiring is correct. I'd check out that dual pressure switch though. Hopefully your refrigerant charge is still good.

I read in one of your previous posts that you're located in Venezuela. Maybe the Galant models were slightly different there, like we've seen with other countries.

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You're right, I was missing the Dual Pressure Switch there, and there's also a Pressure Switch for the Condenser Fan Motor operation so even better. I'll have to check if any of those 2 are still in the car.

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I think you're also right about the Air Conditioning Engine Coolant Temperature Switch and Engine Coolant Temperature Switch. Those don't seem to apply to my particular model and the system should work well enough without those.

As for the Air Inlet Sensor and the Air-Thermo Sensor, it remains to be seen if there's actually something there and if so, if it's working, because the Auto Comp. Control Unit doesn't send a signal until those 2 and the Refrigerant Temperature Sensor are within range. I'll have to find out how to open up the evaporator housing without disconnecting any lines so I can check.

I have bought from RockAuto before, but unless I'm not looking well enough, they don't carry any of these sensors and switches. If you know of any other online stores that could carry this please let me know.

Thanks for detailed response, it helps a lot!

 

[petrosian]

Good luck! I’ve never opened up the housing to see what’s inside. That variable resistor is some interesting work for sure!

Keep us posted on your progress!

 

[sebas-1024]

Keep us posted on your progress!

I think pretty much all of the wiring is as it should now, the condenser fan starts when I "turn on" the A/C (the compressor has no belt so it doesn't rotate), the compressor clutch seems to be receiving power and clicking, and I have the Air Inlet Sensor, Air-thermo Sensor, and Air conditioning engine coolant temperature switch connected to the Auto Comp. Unit, though the latter doesn't seem to be really required as the Compressor Unit was sending out voltage before it was connected, but in any case it seems to be working as far a circuitry goes, I'll try to take it to an Air Conditioning shop during the weekend to see if I can get it working. Thanks for the help!

 

[sebas-1024]

I think pretty much all of the wiring is as it should now, the condenser fan starts when I "turn on" the A/C (the compressor has no belt so it doesn't rotate), the compressor clutch seems to be receiving power and clicking, and I have the Air Inlet Sensor, Air-thermo Sensor, and Air conditioning engine coolant temperature switch connected to the Auto Comp. Unit, though the latter doesn't seem to be really required as the Compressor Unit was sending out voltage before it was connected, but in any case it seems to be working as far a circuitry goes, I'll try to take it to an Air Conditioning shop during the weekend to see if I can get it working. Thanks for the help!

A/C seems to be working well enough now that it's charged and all that, the engine does seem to be idling too low when I have it on though; at about 700 RPMs with noticeable vibration unless I put it on Neutral or Park (The ISC is working fine, so that itself should not be the problem), does anybody know how the ECU gets the signal to increase engine speed when the A/C is on? I'm assuming it's a specific pin, want to verify if it's getting that signal, it would explain the low idle if it didn't.

 

[petrosian]

It’s awesome that you figured it out and got it working!! That’s what this forum is for, and we like hearing success stories like this

For the idle, yes the ECU definitely knows when the AC is engaged (see diagram). It comes down to that dual pressure switch I mentioned way back. The ECU uses that signal to change the position of the ISC stepper to support the extra load of the AC compressor.

Granted, based on the diagram, if your AC is working, it should be telling the ECU that the compressor clutch is engaged. It’s inherent to the way it’s wired (again see diagram). This path also tells the TCU in automatic cars that the AC is active, and it adjusts the shift points accordingly due to the extra load.

I need to take a closer look at the diagrams to give more definitive answer (we’re out celebrating tonight and I’ve had a few ), but since you said the ISC is working properly, it may be an issue of base idle setting.

The vibrational idle is pretty common on automatics. It may help to use the BISS (base idle set screw) procedure below.

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[sebas-1024]

It’s awesome that you figured it out and got it working!! That’s what this forum is for, and we like hearing success stories like this

For the idle, yes the ECU definitely knows when the AC is engaged (see diagram). It comes down to that dual pressure switch I mentioned way back. The ECU uses that signal to change the position of the ISC stepper to support the extra load of the AC compressor.

Granted, based on the diagram, if your AC is working, it should be telling the ECU that the compressor clutch is engaged. It’s inherent to the way it’s wired (again see diagram). This path also tells the TCU in automatic cars that the AC is active, and it adjusts the shift points accordingly due to the extra load.

I need to take a closer look at the diagrams to give more definitive answer (we’re out celebrating tonight and I’ve had a few ), but since you said the ISC is working properly, it may be an issue of base idle setting.

The vibrational idle is pretty common on automatics. It may help to use the BISS (base idle set screw) procedure below.

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Ok, I should be good on those connections then, it does increase the idle when the A/C is on so that shouldn't be the problem. I'll keep looking into the idling issue and probably make a separate post for it. Thanks a lot!