At one of my stores I have 3 Tyler Service Deli Cases.Vertical Perminant Glass front. Do not have the Model Number. Gravity serpentine coil in the bottom of case and traditional aluminum finned coil in the top of the case. No fans all gravity. R-404A, has a Liq Line Solenoid, and a ORIT-PI Valve on the Suction line. The TXV's feed the bottom coil first and the top coil after. It is controled by CPC E2. The problem is that according to the dept manager this bottom coil has been icing up every month for the last three years. I just got this store in March and have been trying to figure out what is going on. I replaced the LiqLineSolenoid, it is working properly. It has one defrost for 120minutes every 24hours as per the specs. The PI valve is set at 55psi. Anyone run into anything similar or have any advice? Thanks.