Where is the low side port?

The low side port is in plain view: Find the inverter coolant reservoir. Note the metal pipe running under the reservoir. That is part of the low-side AC plumbing.

Look for the inlet port on that pipe, which is covered by a grey plastic cap with L on the top. The port is also near the orange high voltage cable that runs from the AC compressor to the inverter.

I hope that you are aware that the Prius AC system uses special refrigerant oil which does not conduct electricity, so be sure not to use refrigerant that is premixed with regular refrigerant oil. Use of such oil will destroy your electric compressor.

 

What's the max psi you can charge the low pressure port too. I live in texas and mine is reading 40psi. I'd like to get it to 50psi. would that be ok?

 

This is the spec for AC system pressure:

Test conditions:

Temperature at the air inlet with the switch set at RECIRC is 30 to 35°C (86 to 95°F)
Blower speed control switch at ”HI” position
Temperature control switch at ”MAX COOL” position
A/C switch ON
Fully open doors

Gauge reading:

Low pressure side:
0.15 to 0.25 MPa (1.5 to 2.5 kgf/cm2)

High pressure side:
1.37 to 1.57 MPa (14 to 16 kgf/cm2)

0.25 MPa = 36 psi so your idea to raise the pressure to 50 psi will result in system overcharging.

 

The high pressure side is the one that really matters. 250 psi is OK. 300 should be max.

If you go to 40psi, when the compressor is running, it is overcharged or the compressor is not working, and the high side is low.

35-38/275 is a good reading at 85 degrees F.

Unless you have a special valve that allows charging liquid refrigerant to the low side, only gas should be introduced to the low port.

A sauce pan of 180 degrees water can safely be used to heat the can to move the gas into the system faster. But be careful, if you have NEVER serviced air conditioning.