I operate a 9500lb R-507 system. My issues are as follows. 1. Excessive ice build up beneath my primary transfer vessel where the check valves are. 2. In the summer, my Control pressure receiver an low pressure accumulator practically switch places, meaning my average 18'' of liquid switch from the CPR to the LPR. I cannot indicate or verify that the check valves are leaking by in any way. Nor is the system trying to transfer refrigerant irregulary. Information on this would be great thanks.