Low side with extreme high pressure

[Rooster71]

I have a 2011 Mitsubishi Lancer Sportback. I was doing some other maintenance and had to have the a/c system emptied. I am attempting to charge it, but it’s not working. I have the required amount of refrigerant. With the compressor on, the low side has 70 psi. High side has 450 psi. When the compressor turns off, the low side goes to over 100 psi and high side drops to 300 psi. When I turn the car off, the low side goes to the max of 320 on the gauge! Nothing was changed. I did pull a vacuum and no leaks. I have done this before, but this has me stumped. Any ideas?

[JohnHere]

This sounds to me like an overcharge condition. The specs for your vehicle call for 18 ounces (1.1 pounds) of R-134a and 3.4 ounces of PAG-46.

With the charge amount being so small, it's pretty easy to overcharge a system like this. If you're using the individual 12-ounce cans of refrigerant and not weighing them on a precise refrigerant scale to ensure that the correct charge amount goes in, then the probability is high that you overcharged it. Just an ounce or two over the spec can result in poor performance and sky-high pressures, especially on a low-capacity system.

I did pull a vacuum and no leaks.

Bear in mind that a system that appears to be leak free under vacuum is no assurance that it won't leak under pressure.

[DetroitAC]

Air in the system, you made a mistake somewhere in the vacuuming, recharging. We all make mistakes, can do this for 30 years and still make an oopsie.

[tbirdtbird]

Wonder what kind of vacuum pump, a Horrible Fright venturi type that runs off compressed air (junk) or a real pump that has an electric motor