2006 M35 AC system working but not reading correct pressures

[tacomaguy20]

I have a 2006 Infinti M35 and the ac was working fine. AC at the vents was down to 40 degrees in 90 to 100 temps. Well I should have left well enough alone but I got myself a new manifold gauge so I decided to test it on my car to see what pressure it was reading to see if the gauge was accurate. It seemed a little low around 40 in 105 degree heat (tested with my other gauge as well) so I went to add some refrigerant. From what I understand for the temp it was at the time it was supposed to be over 50 psi on the low side and 250 to 320 ish psi on the high side. I have the chart somewhere just giving a range as the temperature was fluctuating. Well my high side pressure was 150. I thought that was way off but from what my searches told me if the AC is too low then the compressor doesn't get it up to the high pressure so I added some refrigerant but no matter what the pressure didn't raise. I thought the refrigerant bottle wasn't dispensing correctly or that I was doing something wrong but before I knew it I added the whole can. The numbers haven't changed at all. I'm guessing something is wrong (and the AI search bots tell me something is wrong) but I'm wondering why the AC was working just fine before I messed with it? I'm pretty sure I overcharged it because it doesn't cool nearly as well as it was before. It gets down to about 57 degrees now. Did I mess up my system or did I just detect a problem early before it left me without AC?

[VStar650CL]

You probably just need to let out the excess you put in. The ECM shuts down the compressor when the refrigerant pressure is too low or too high, so overcharging will shut it down just as reliably as emptying it.

For reference, at room temperature your low side should run 35-ish and your high side 120-ish. That also depends on humidity, so there's a range. See ATC-104 here:
https://www.nicoclub.com/service-manual ... %2Fatc.pdf

Your compressor is a swash plate type that will run whenever the A/C is on, so you should see little or no variation in pressure at idle. It won't cycle, the IPDM just orders more or less swash according to the demand.

[tacomaguy20]

Thanks for responding. I checked the chart and the temperature is a lot higher locally (AZ) than the numbers you gave me. It seems that you were referencing colder weather. I am looking at the manual and it says in 104 degrees (It's been around there but also hotter certain days) and it's saying a pressure of 48-58 on the low side and 186-229 on the high side. The problem is that my pressure was lower than this in hotter temperatures before and after I added refrigerant. It went up slightly but still did not reach the numbers that it should be. I reved the engine to 1500 to 2500 rpms before adding refrigerant and when I did that pressure dropped even lower on both sides. After adding refrigerant I got very little change so it makes sense that the system is overcharged now but why am I'm not able to see that reflected in the pressure numbers? Even if the compressor is shutting off, the low side should be showing that it's overcharged correct?

Basically it seems like my system is working but not reflecting the correct pressures and I'm thinking that something may be failing because why else wouldn't the pressures change after adding a can and it's obviously overcharged? It doesn't seem like a common thing for someone to not be able to read correct pressures unless something was wrong.

[VStar650CL]

Yah, those figures were assuming room temp in a service bay. Sonoran Desert in May will definitely read higher.

Couple things. First, if it's overcharged there's an easy test for it. Get a spray bottle of water or a garden hose set on "mist" and spritz the condenser. If you get a sudden blast of cold air and then back to warm, it's overcharged.

Second, if it isn't overcharged, your compressor is a swash type. Swashes usually fail with the plate at minimum stroke. There's also an easy test for that. Turn the blower to the lowest setting and see if the outlet temp suddenly gets cold. If so, the swash is stuck at minimum and the compressor can't move enough volume to meet the cooling load. If that's the problem, the compressor is toast.