Found Walk-In Freezer evaporator pan and drain line frozen solid, also drain line not insulated keeping drain line heater from doing its job, checked defrost and drain line heater and both working properly, I removed drain pan and removed ice and thawed drain line, I reconnected drain line with PVC coupler, I also wrapped drain line temporarily with foam tape, need to order 1 piece of 7/8" x 1 1/2" Armaflex and return to insulate drain line better, working properly at this time. 4/17/19 Returned to insulate drain line and found drain line and pan frozen up again because drain line not insulated and evaporator frosted over, thawed drain line, pan and evaporator and insulated drain line, also checked defrost again to make sure it is still working and it is, unit is working properly at this time