my experience charging the refrigerant (prius ACs are leaky)

this spring, AC became very weak and the compressor was making gurgling noises on a start up. i checked the sight glass and bubbles galore, even in mild weather. i understand from reading here that other 2010 prius had loss of refrigerant too at this 9 year old mark. interesting, i have/had much older toyota or or non-toyota cars and no refrigerant loss in those. because of that, i used a can of R134a with a leak stop, but without compressor oil. i used a leak stop in my home AC unit like 10 years ago and that saved me $5000-10000 with no complications.

now, i do have 2 AC manifolds, but i used one on another car some time ago and the other one on a home unit, so i didn't use them on my prius due to the oil contamination issues. instead, i purchased a $15 low pressure house with a pressure gauge.

surprises: the low pressure even with clearly low charge was nominal at 35psi. that confused me a bit, but i went ahead with the charging. the pressure fluctuated, but would quickly go back to 35psi. at a mid point, suddenly the compressor went into high RPM, and the condenser fan did that too. i finished the whole small can (10oz) and the pressure did not go any farther, and stayed at 35psi. the AC works much stronger now, with no noises, or bubbles, but not as cold i would like. i'm still probably undercharged. I may need to purchase another AC manifold to check the high pressure that is probably more revealing.

i'm thinking the compressor effort depends on the charge and the low pressure is regulated and can't be trusted for the optimal charge decisions.

 

i agree with everything you said, except coolant is for cooling the engine or such.
as a matter of fact, when i unscrewed the low pressure valve cap, there was clearly some pressure under the cap.