2011 M56 - AC stopped working

[Ilya]

My old M is starting to show it's age. I have the ongoing P0420/cat issue (see this thread) and now this...

So, having not used AC for the last 6 months due to living in antarc...I mean, New York...it's warming up now and it's time for AC use again.

The first time I tried to turn it on this season, I had no cold air blowing. Just 'room temp' air. I bought one of those self refill cans at Autozone and filled her up via the Low pressure nozzle and it started working again. Now, a few days later and another warm day, no cold air again. Looks like my refrigerant is leaking out somewhere.

When I connected the self refill thingamagig back to the L port, it told me my pressure with the car running was very low (~15-20psi). It's supposed to be like 40ish IIRC.

What might be happening? How does one find a leak? Or could it be my compressor (I don't seem to feel/hear it kick on - usually the RPMs will dip if you're idling and the AC comes on, right?)? How expensive/hard will this repair be for those who've done it?

[satown210]

Start by looking at the A/c compressor, the lines, and the condenser for a dark oily or wet spot. When there is a leak, the oil in the cooling system usually leaves a mark where it is coming out. A lot of times from the factory, there is a bright yellow dye in the a/c system. Look for a bright yellow or green on all the a/c components. Other than that, a shop will do a visual check, inject dye and try to find it with a black light, or they will use a sniffer tool. Unless it's the evaporator (which it rarely is) you should be able to find the leak by looking.

[Yoda's Master]

you can get the can with the uv dye. and use a uv flashlight to look for leaks. you could also try filling with the can that has o-ring conditioner in it or leak-stop. conditioner is better since it softens the oring again

[EdBwoy]

...
Or could it be my compressor (I don't seem to feel/hear it kick on - usually the RPMs will dip if you're idling and the AC comes on, right?)?

Yes, typically you can hear a very audible click coming from your engine bay when the A/C compressor clutch engages. Open your hood to hear better, and play with the A/C button on your center stack.
Also, you can visually look at it to see if the clutch is running when the A/C button is pushed.

If your system worked for some time after you refilled it, maybe the compressor is actually working OK, but I'd do those simple observations to see if it engages first. Process of elimination.



As an aside, but very important:
A lot of people confuse A/C with cooling.
Back in the day, some owner's manuals actually had it written in the literature that you should run your A/C system for at least 10 minutes every month. In the most rudimentary of benefits, that kept your A/C compressor healthy by frequent oil circulation. On a different level, the laws of physics allows A/C to be run at any time of the year.

So, having not used AC for the last 6 months due to living in antarc...I mean, New York...it's warming up now and it's time for AC use again.

Do you actually push buttons to ensure that your A/C light stays off?
When you select your front windshield defroster for example, the A/C system automatically kicks on when the ambient is above 25*F or so, but I suppose you could force it to turn off as well.
The A/C system can (and ideally should) be let to run all year round.
Nissan vehicles have had an AUTO button for quite a long time. That button takes the guesswork out of a lot of situations and I usually set the temperature then let the AUTO system do it's balancing. The only adjustments I make are temperature up or down.
So, even in the winter I might hear the compressor clicking on and off, but never has my car not returned the cabin temperature I asked for.

[Ilya]

You're correct Ed, it was a matter of wording. My 'AC' is technically on all the time, but my COOLING hasn't been used in months hahah. I do use the auto button almost exclusively. My heat is working great, but my cooling is, if I had to guess, around 75ish.

I will likely go to a shop and have them put the dye through, etc. but I will do a visual inspection for anything obvious when I get a minute.