When do you need to add oil in a compressor?

When you try to check your freon level on the low side (blue gauge ) feel it with your finger and if you see no leakage or oily deposit most likely you are okay but if you see oily deposit then you may want to add a couple of table spoon oil to your compressor . Compressor normally need gas more than they need oil . If you are losing freon on a normal basis you should get license heating and airing guy to check your unit . Also listen to the sound of compressor often because too loud compressors are usually on their last leg .