I recently got my AC working again (finally) in my 07 G35, and I noticed that when I drive it hard (redline) it shuts off the AC compressor and won't allow it to turn back on unless I restart the car. Is this normal on these? I had replaced the expansion valve and charged it, everything is working well and pressures look good on high and low sides. I noticed on my scan tool the ECM kills the AC clutch command when I rev over like 6500-7k RPM, which would make sense, however typically this should turn back on when the RPM is within what the ECM deems to be a safe operating range for the compressor.

 

Somewhat related but on an EG Civic - I had the same condition, and it was a faulty ECU.

You are correct that the A/C compressor should shut down - typically under WOT or high rpm (5000+?). Outside of both those conditions the compressor should kick back on (for the Civic, the ECU provides ground to compressor clutch relay). Again, in the case of the Civic, I checked literally ever part and nearly every inch of wire, eventually was able to swap ECUs with a *suspected* working ECU and the problem went away. Again, 'dinky little Civic' disclaimer, but you may wanted to investigate a broken soldered joint in the ECU.

Good luck - AC can be a chore, but it's worth it!

 

Thanks! I had a similar thought, that maybe something in the ECU was causing it to stay off. Either way, I don’t think it’s a pressure switch or anything, since that voltage doesn’t change when the problem occurs. I think that the compressor is cutting off when it should, and the problem is that it needs a key cycle to allow it to kick the compressor back on.

I’ll check the FSM for any more info. Worst case I might have to send out the ECU for a repair. Wouldn’t surprise me, I work on BMWs primarily and I’ve had one car after another in my shop lately needing ECU repairs, so what’s one more? lol

 

Yeah key cycle allowing it to reset is what triggered the memory haha. On hot days I spent a of time time watching the revs/throttle to make sure I didn't trigger it.

The fact that the AC works at all pretty much guarantees all the sensors, relays, switches yadayadayada are all functional. Thinking more about it, if the clutch was somehow sticking on it could over-pressure or freeze the evap/thermostat, but each of those conditions would resolve after maybe 30min max and start working again.

 

Yeah, I'm thinking if it thought there was a freeze-up or something of that sort, the sensor wouldn't normalize just from a key cycle. Then again who knows, the electronic portion of these cars hasn't failed to surprise me yet lol.
Over pressure is a possibility, but oddly enough that only happens after the AC cuts off. Pressures look great while running, when off (after it was running) low side spikes to 150 PSI or more, at least briefly. Resting it's just over 100, but it's also been in the mid to high 90s ambient temp, so that's something to consider.

 

I checked on my scan tool again today, and it definitely shuts off at 7,000 RPM. Driving around the other day, I had no problems with it until I accelerated and wound it up over 7k, then cycled the ignition and all was well.
Can anybody confirm if this is normal or not? I find it very strange that I have to cycle the key to get the compressor to turn back on. Either that or Nissan figured if you're driving it like that, you won't be using the AC.

 

Not normal. My 07 shuts off and comes back on after few seconds when the RPMs drop to below 5k. You might have a sticking high pressure sensor on the high side line as that's what turns off the clutch. Or it could be something inside the AC comp or somewhere on the line that prevents the AC pressure from dropping faster. (ECM gets signal from high press sensor and triggers IPDM to shut off the AC comp i suppose) Did you check if the AC comes back on after few minutes without cycling the ignition?

 

It does not come back on. When I drove it the other day and it shut off, I was about 5 minutes from my shop and by the time I got there the compressor still hadn't come back on.
I thought that as well, I figured it related to pressures somehow. I did put a used pressure switch in it as well as a new compressor, but I'm pretty sure it was doing this before.
I logged the sensor voltage during this, and I don't remember it changing at all, I think it stayed right around 3.74v (could be wrong).

I know the pressures were pretty high on the car for some reason, while it's running they look good but once the AC shuts off the low side will go upwards of 120 PSI after a minute or two of the compressor shutting off. It was a pretty hot day when I checked, so there's that, but it was still a little too high for my liking. The system is slightly under charged as well, I believe I only filled about 430 grams.

 

What about cycling the AC switch Off and back On? It might be a faulty Unified Meter & AC Amplifier module. Mine did crap out and took out the evap coil freeze sensor with it.. I'd start with that before ECM..

 

Interesting there was a failure there, I wouldn't be surprised if that's my issue too. I wonder if I can disconnect the amplifier after it cuts out to check that, maybe that's what needs to power cycle.

 

I checked the pressure sensor, and while I can't find a voltage chart, it sits around 3.88v while running the AC. The value changes within the 3.8 range, but nothing drastic. Voltage does NOT correlate with the compressor being shut off. The only factor in shutting off the AC clutch is running over 7k RPM.
I really hate just throwing out guesses, but it seems to me like the ECM controller (however it handles this) isn't turning the compressor clutch back on after going over 7k RPM. The only change when this happens is that the ECM shows "off" next to the AC on signal, and of course the AC clutch relay.

 

Check HERE to see if there is an update for your ECM. If there is, you can follow my GUIDE in updating it at home.

 

Thanks! I'm going to check the part number tomorrow.