Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
If the bad valve is on the low side and you don't have access to a recharging station that has high and low side fittings, you can't recharge it. You need to have a completely discharged (preferably recovered) system in order to replace the bad valve or the line that the valve is in. If it is already totally empty, you will need to replace the bad valve and then yes you will need to put a vacuum on it for at least 3 minutes. You shouldn't have to worry about adding oil unless it showed signs of leaking out the oil.
If the system is completely empty, pull the vacuum using a vacuum pump and add the amount of R134a specified on the label which should be under the hood somewhere. If you can't find your label, let me know and I can find the recharge specs for you.
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You should pull it on both sides, but the entire system will evacuate just fine if you can only pull in on the low side.
If you don't have a recharging station or a gauge set with fittings for high and low side, you are stuck charging on the low side only.
You need to charge on the low side because the compressor running is what creates the low pressure on the low side which allows the R134a to be drawn in due to the lower pressures.
Hope this helps you get thing cooling again.