R-134a expands more under heat and pressure because of the molecular (I can't spell, lol) structure. It is recommended 80-85% of r-12 specs. However, This will result in a warmer interior.
The pressure switch is the Low Pressure Cycling Switch. It is set by the factory to turn off the system at 25PSI and turn it on at 42PSI. If you are overcharged, the pressure would not drop low enough for it to ever turn off.
I assume we are talking a Fox here. From the factory, the system has a high-pressure blow-off valve right at the compressor. If your pressure ever gets too high, it blows gas out of that valve.
Otherwaise, if the person doing a retrofit did the complete job, there is a high-pressure cutoff switch.
Too much of a charge will hinder the cooling as well as a low charge. Put a set og gauges on the system and adjust as needed.
Last time I did mine, it took 2 cans R134a, which figures out to be 24-28 oz. That is a complete recharge with a good vacuuming prior to recharging. It cools really good now.
Well... I pulled a vaccum today, and emptied the system. Then I started recharging it, and after about 12 oz, the clutch was running a full speed. the pressure started to shoot up, so I turned the car off... and when I turned it back on, the clutch wouldn't come back on, and the pressure was quite high, about 100 psi, and wouldn't come down. I jumped the clutch, and the pressure still wouldn't come back down. So I pulled the system down again, and started refilling it... once the freon started flowing in, the pressure spiked... Needless to say, the clutch didn't kick back on, and now I'm sorta stumped. I'm just gunna take it to an a/c shop and get assraped... but it's Florida, I need a/c.
Could be a stuck orifice. Always replact that. Also-a long shot- but hopefully you didn't burn the clutch up. Should have put the freeon in before starting the car. You may have burnt your compressor up running it without oil.
Note: you can check the condition of the compressor by running 12 V's straight to your compressor. Clutch should kick on. If not it's trash.