I am working on a unit that has two compressors built in to one evaporate coil. So two circuits. Compressor one operates as usual and compressor two kicks on only when there's heat rise and the first compressor can't handle it. My problem is compressor one runs normal at 60 degrees,but when I set the temp to 40 compressor two kicks on and then compressor one starts to freeze at the suction line. I checked the super heat and subcooling and got 10 degrees roughly. So I'm assuming the charge is good. Also I assume this because I used a vtech which is very accurate. So it's not overcharged so I'm thinking airflow. It has a new filter and a new fan so my question is, it's about 70 degrees in the mill so I think the air might not be warm enough passing over the coil to change the refrigerant back to vapor. So there for I'm getting liquid in the compressor. This only happens when circuit two comes on and rapidly cools the coil. When circuit one runs by itself it goes away. Is there anything else I should look * The Txv's we get come preset, so I dont want to touch those until I know for sure it's not airflow issue. Any suggestions would be appreciated. I'm kind of new at this also been doing it for about a year so i have a lot to learn.