2010 Prius with AC acting up...

To properly fix this you would need to evacuate all the refrigerant in the system and reload it with the proper amount (using a proper machine). The prius is really sensitive where even the slightest amount of low or too much refrigerant would cause the problems you're experiencing.

I know a shop in Rosemead that can do that fairly quickly, while you wait;

 

Yes I'd be interested in your low side gauge reading with the car off not running just sitting there looking at us You got about a hundred pounds?

 

What JC was getting at is that trying to judge proper charge with just a pressure gauge is highly unreliable, for reasons heavily discussed already in a lot of threads on this site.

If a gauge tells you it's low, it probably is really low. But the gauge telling you it's ok only means it's somewhere in a wide range between inadequate and overcharged.

Older cars that took a larger amount of refrigerant were more tolerant of a bit of slop in the amount of charge. Because the Prius uses such a small amount to begin with, it doesn't take much variation below or above to cause problems over time. @lech auto air conditionin may expound further.

The most reliable way to get the proper amount of charge in is to go to vacuum first, then weigh in the correct amount of refrigerant using a scale.

If you didn't have your can on a scale as you were adding just now, then you've added an unknown amount of refrigerant to a low-but-also-unknown pre-existing amount.

The most reliable way back to the correct charge from that situation would be to schedule a visit somewhere that can take it to vacuum and then weigh in the proper amount.

 

The the ideal way, but you just added a very small amount, and it worked, for now.
There is a small leak. Probably the seals are worn, and freon escapes...
See how long it lasts. You can always add a little more later on.

As you said, it's an older car. You work on your own car. You do what you need to do.
Doesn't matter what anyone else thinks.

 

It's not a matter of the gauge being far off or not. It's a matter of a gauge not being the right instrument, period. A pressure gauge by itself cannot tell you if the amount of refrigerant in the system is correct.

The reason there's so much discussion here on PriusChat about that is that there are dangers from being on either side of the correct charge. And while a pressure gauge can tell you if the charge is extremely low, once you get the charge back above extremely low, the gauge is just unable to tell you whether the charge is right or not.


... what's frustrating is that the Gen 3 ECU probably has enough information that it could compute whether the charge is correct, and tell you that. It has a high-side pressure sensor, not just a switch, ambient and evap temperature thermistors, and it knows the power being provided to the compressor. If I'm not mistaken, they did add that computation to the firmware for Gen 4, and a Gen 4 can tell you if the charge is ok if you ask. But not yet Gen 3.

 

You doing okay for what you're holding. Gas it up and go just realize these things will never hold a 40 lb low side it'll be more like 30 just the way it is or it's what I see here anyway pretty consistently if that compressor's coming on high side is rising the low side will get sucked down to about 30 anytime the compressor is running when it's all for idling or wobbling way down then things change of course which is the beauty of these things.

 

Some people lucky some people not on topping off being too full or little too low.

it’s only a gamble. I and many shop or parts stores make lots of money off the unlucky ones.

a little low then the compressor just runs hotter and faster on hot days to make up for the lack of refrigerant. That’s all. It still gets cold. On vary hot day the compressor will max out RPM’s in a attempt to move enough refrigerant to satisfy the desired temperature that was selected. But because it’s low on refrigerant I cannot so I continue spinning at 6000 and 7000 RPMs nonstop trying to hire amptra after high voltage battery continuously drawing down the high voltage battery because it never gets a rest because of the low refrigerant charge..
Some compressors live through this for a few summers, and some do not.

As the refrigerant slowly get lower do to a small, slow leak it gets to a point where oil leaves the compressor and starts not returning because it gets stuck up in the Evaporator, because low mass of refrigerant cannot keep up the velocity to remove the oil out of the evaporator. I only can do this so long until it cost to live for the compressor..

Turn too much refrigerant has a similar effect. Which is higher pressure and higher temperature but at least there is oil return.. but also because there’s more refrigerant to oil ratio it’s diluted.

on an AC system that’s never allowed to go low on refrigerant. You should be able to run the compressor continuously 10 hours a day for 10 years straight never turning it off and it will still be in perfect condition because it was always ran cool with plenty of oil..