AC High and Low Pressures at elevated ambient temps?

[re_guderian]

So if I'm reading the manual correctly, the correct procedure to measure refrigerant pressure is to set AC to max cold, recirc, max fan, open doors and engine at 2000 RPM. Specified air intake temp is 86-95 degrees. With that set up, low side should be between 21-35 PSI, and high side should be between 199 and 213 PSI.

No problem on my '00, i just grab the the throttle cable and give it a tug until Torque tells me I'm near 2000 RPM and I read the gages, but where exactly are you supposed to measure the air inlet temps? Is that at the passenger's footwell? If so, tonight it was between 105 and 113 degrees. Given that it's hot as heck here right now, what should be high and low side pressures be? I see many charts on the interwebs that say 50-55 PSI low side and 330-335 PSI on the high side for a 105 ambient. Is that right??? I also found this chart that takes into account RH. Is this correct? FSM a little shy on details here. We can't all live in Shangri-La...

I set to factory specs yesterday (when ambient was also surface-of-the-mother-fracking-sun hot) and rear AC was non-existent and front was marginal today. I had 45 deg vent temps when driving fast, 50-70 degrees when stopped. Injected dye tonight, no leaks found. Not dripping water from the evaporator onto the driveway, but it's also only mid-teens for relative humidity, and dew points in the 30's to low 40's. None of my cars are dripping right now. If I'm now at 45 PSI low and 275 PSI high at 2000 RPM, am I about there, or overcharged? Half tempted to go get it evacuated and just start over.

 

[fooldall1]

Did you ever get this figured out? I'm exactly where you are right now. 70 in the rear and 61 front at idle- 50 or < at vent while moving. At night or after a rain, cooling is fine. Yesterday when it was like 110% humidity and 105, the rear air felt like it wasn't even doing crap and the front was only slightly cool. My wife, sitting in the rear was saying it's not cool at all. I'm tempted to just add freon until the temps get to where I want them to be since they seem to be able to handle much higher pressure by default. It's Africa hot here in FL with super high humidity to boot.

 

[re_guderian]

Did you ever get this figured out? I'm exactly where you are right now. 70 in the rear and 61 front at idle- 50 or < at vent while moving. At night or after a rain, cooling is fine. Yesterday when it was like 110% humidity and 105, the rear air felt like it wasn't even doing crap and the front was only slightly cool. My wife, sitting in the rear was saying it's not cool at all. I'm tempted to just add freon until the temps get to where I want them to be since they seem to be able to handle much higher pressure by default. It's Africa hot here in FL with super high humidity to boot.

No, I'm still running as-is. It will get down to 40-42 degrees from the front vents, 60 at the rear. I've seen some really wonky behavior when I overcharged with the stupid gauge-on-a-can. Don't want to risk that again. I will either a) wait six months for ambients to hit the FSM range, b) use my handy-dandy front axle bearing fish-scale and SLOWLY add an ounce at a time to see what happens, c) tear apart the rear evaporator and see how nasty it is after 18 years and 250K miles, or d) just deal with it. It takes about 5 minutes or less to go from 120 front vent temps to 40 vent temps. I don't think that is "THAT" bad. Right now, I don't have anyone traveling in the rear seats, so not terribly concerned.

 

[Spike555]

I think you're overthinking it, I have never raised engine RPM, worried about air intake temps etc.
Are you comfy when driving? Then it's good.
As far as the rear goes, I think thats just more of a complement to the front than actual climate control for the rear otherwise it would be electronic too.
I think of it as putting a box fan in the hallway to suck the window a/c from one end of the house to the other.

 

[fooldall1]

It seems to me, that in this heat/Humidity 50-55 Low side cools better. However, the Factory recommendation is based on a simple "fill weight" which, i measured yesterday at 95 degrees and near 100% humidity and it was closer to 45lbs. That said, the temp at the vent was right at 40 degrees while moving an slightly higher when not. Does it stand to reason that a little more gas needs to be added for more extreme climates like FL in the summer?

Experts, please chime in.

 

[jerryb]

I'm no expert, but I do mine at night in pensacola. I stay at the very upper edge of the book temp, around 90° outside. High humidity. I stop mine at the very top of what the book says (2007 fms). I have a pic somewhere. I stop at 35 and 235psi. My vent temps are.. I don't know what they are actually on fresh air setting. I check after I remove the fill whips. I don't walk away from the lines.
On recirc I have 29-31° in the dark. I've had to do it a few times. I have a scale but it seems pointless to me unless I was evacuated or replacing parts.
My evap drips like crazy 100% of the time. I even try to park downhill slightly so it doesn't back up and into the gasket on the cover.

 

[fooldall1]

I'm no expert, but I do mine at night in pensacola. I stay at the very upper edge of the book temp, around 90° outside. High humidity. I stop mine at the very top of what the book says (2007 fms). I have a pic somewhere. I stop at 35 and 235psi. My vent temps are.. I don't know what they are actually on fresh air setting. I check after I remove the fill whips. I don't walk away from the lines.
On recirc I have 29-31° in the dark. I've had to do it a few times. I have a scale but it seems pointless to me unless I was evacuated or replacing parts.
My evap drips like crazy 100% of the time. I even try to park downhill slightly so it doesn't back up and into the gasket on the cover.

View attachment 1799400

Those Fill settings are assuming what ambient temperature? it can't be one size fits all, can it?

 

[jerryb]

I stay at the very upper edge of the book temp, around 90°

it's in the book on the opposite page I think. I wrote those temps down for me for this weather.
you want me to look and post it?

actually the book doens't say. Just that line about 1500rpm and 86-95°F