Icing Evaporator

[brad72]

Hi,

We have a cold room approx 3mx3mx4.5m high running @ a set temp of 1-4 degrees Centigrade. The Evap unit is a twin fan Muller MLV100, running on R404a gas. The compressor is a copeland running 1 other room and a a freezer. The Room cycles in/out throught the control of a bulb thermostat, opening and closing a solenoid in the supply line.

The problem we are having is the evaporator coil continuously icing, which will cause flood back to the compressor, icing it up as well. I then have to isolate the solenoid for around 6 hours to allow the unit to defrost then switch it back on again. I have cleaned the evap coil, checked both fans for air flow, which seems low but not bad. the tx valve bulb is in place. Drier was replace about 6 months ago (the drier runs all 3 rooms). The evap may take a week to ice or it might take 4 hours after a manual defrost.

The evap coil is old and was desighned for the older gasses, not the R404a. There is no defrost fitted but the room has run fine like this for years. The door seals are in sound condition and no other room leaks can be sighted but being an old room there may well be.

My question is, Would a new evap coil fix the problem ($1500 fitted), or are there some other steps that can be taken to solve the problem eg. new tx valve?