I have a 383 Massey ferguson. The air conditioning system has been switched to a r134a system before I bought it. The consensor developed a whole so we have fixed that and are replacing the dryer and expansion valve. Just wondering if we need to an oil to the system before we vaccum and recharge it. The compressor was not replaced. We have cleaned the system just wondering about the oil. Also the compressor says sp-10 oil and has no capacity amount listed on it. Our tractor manual is for an r-12 system so it doesn't help me. The compressor is a sd7h15 sanden. Do I need to take the compressor off and drain oil? Do I leave the compressor on and add oil? Seems to be important not to have to much oil in system. Thanks in advance!