I have a 03 Max with auto A/C. The problem I am having is the A/C compressor never shuts off. It doesn't matter if it is set on auto, econ or off, my compressor is turning! I have been trying to troubleshoot this all day. I even disconnected the wiring from the Auto A/C unit and no change. The compressor will disengage if I pull the AC fuse under the dash or the one under the hood. I also switched the A/C relay for the one for the fog lights (which I know this one works) and no change. I know the ECM actually controls the A/C clutch but I am having a hard time believing it is bad. The car runs fine.

Thanks for your help,
Gears

 

sounds to me, like a clutch problem or a short somewhere to the magnetic.

see if this clip helps:

https://www.youtube.com/watch?v=04c1MPq0HGo

 

Thanks for the video. I do not have any clutch noise and the clutch will disconnect if I pull either AC fuse. I havent ruled out a shorted wire yet.

 

The way Nissan designed the system is that the heater-a/c control panel sends a signal to the ECU and the ECU checks for a few things and then energizes the Air Conditioner Relay. The relay then sends power to the compressor clutch.

When you pull the fuse under the dash and the a/c compressor stops turning, this eliminated the relay as the problem.

This leaves the heater controls and the ECU. Going by probabilities, the heater control unit (Nissan calls this the a/c auto amplifier) is more likely to be the cause than the ECU.

You would have to check voltage on the wire from the heater controls to the ecu. On the control panel, it is pin # 22 in the smaller of the 2 connectors, a green/black stripe wire, 2nd in from one of the corners. On the ECU, it is pin # 45.

I am not going to describe any further electrical troubleshooting unless you can do this and have the equipment. Let me know.

 

Thanks for your reply,

Yesterday I checked the voltage at the AC auto amplifier and got 2.2 V on the green/black stripe wire at pin 22 and 0 volts on the purple wire at pin 8.
I haven't checked the ECM side. Do I need to check this side?

Gears

 

I verified this again before going to work today, with the engine running, the compressor on, A/C set on "auto" = 0 volts at terminal 22. Same conditions except A/C set on "econ" or "off" = 2.2 Volts at terminal 22.
Again the compressor stayed on no mater what the A/C was set on.

 

Do you have the vents set to blow up at the windshield? Defrost? If so, the compressor will kick on automatically, regardless of the temperature. Regardless of whether the "AC" is actually on.
If it is 0 degrees outside and you set it to defrost your windshield, the ac kicks on. It doesn't function to create cold....that is NOT the sole purpose of the system. Just like on your home, the compressor will kick on to 1. cool the coil of the inside unit in the summer or 2. heat the coil of the inside unit in the winter.

Although your home has electric coils to help in extreme cold in winter, your car does not. Our car's heat in the winter is actually a bit different, it uses the AC system to create some initial heat, but our engine coolant is the primary heat the system uses once the car is warmed up.

Again, if you leave your vents set to defrost, your compressor is going to run. Turn your vent settings (regardless of temp) to the floor and make sure the AC is off. Then let us know if your compressor still runs.

 

Dennis knows his stuff.

Sounds like a Thermostat Control Issue.

Check this Vid on bypassing your AC control system.
https://www.youtube.com/watch?v=ah4OEeCu1KE
https://www.youtube.com/watch?v=ah4OEeCu1KE




.

 

No the Auto AC is not set on defrost. Also if the controls are set to "OFF", where nothing is running on the Auto AC control, the compressor and the radiator fans are running. This leads me to believe that this is ECM related. As Dennis mentioned the ECM directly controls the AC clutch by grounding the AC relay (coil side) circuit via pin 21.

 

Reading > me. Re-read, I see now. Read off as just turning AC off, not the system. Dennis has it!

 

Thanks for the video. That's interesting. I was thinking about putting a switch on the AC relay circuit to turn it off and on. I very confident that will work. I just want to see if I can do it the right way first.

 

The 2.2 volt reading on pin 22 is not normal for either the a/c on or a/c off.

When the a/c is on, pin 22 should be 0 to 1 volt (more like half to a quarter volt). When the a/c controls are off, pin 22 should be 12 volts.

This points to the a/c auto amp (heater controls) being bad.

 

Ok, I "think" I may have found the problem. I was investigating why the voltage was so low on pin 22. I was actually thinking that the Auto AC was working since it was changing the voltage between Auto and Econ/Off steps and I was getting zero voltage on the right setting. I went to pin 45 on the ECM where the green/black stripe wire goes to. That wire was deep in the harness but I was able to check the voltage. It was reading 2.4V at first. Since this a tough spot to get a reading, I had to move the harness around a lot. Then my reading started creeping up. Next thing you know I had 14V at pin 45! I checked the auto AC and everything started working properly. I checked the volts at pin 22 and got 14V (engine running)! I am guessing I had a loose pin or a dirty connection at pin 45. It has been 24hrs and it is still working. Thank you God.
I hope that is it...

I big thanks to all who offered input, ideas and help! This was a tuffy for me.
Gears

 

Awesome Work Gears....!

This is a great forum...!