John0246

[john0246]

Hey guys, had a look at a walk in freezer. The system is on R404a. Evaporator iced up due to defective thermostat, the liquid line drier was also blocked as I had a low suction pressure. Replaced the drier and thermostat, defrosted the evaporator but its still icing up. Checked the heaters and they draw 3.2 amps each, any ideas what would cause this.

[cadwaladr]

the drain is clear i presume,this could cause the fans to whip the water straight back on the evap if it does not get away

[passandscore]

Is the whole coil icing up? If so:

Is the defrost clock setup correctly? Is the defrost period long enough? Do you have enough defrosts per day? Does the defrost terminate on time or temperature? If temperature, perhaps that termination control needs to be tested.

Do you have proper airflow across the evaporator?

If the coil is only partially icing up and it is occurring from the outlet of the txv throughout the first half of the evaporator, you are then low on gas.

[PaulZ]

Hi John
Have you checked the TXV bulb location?
Have you checked the TXV superheat?
Have checked the charge?
have you checked the condenser is clean?
What are the operating conditions?
There are many reasons that an evap will ice up, some more info would be good.
Paul

[frank]

Hey guys, had a look at a walk in freezer. The system is on R404a. Evaporator iced up due to defective thermostat, the liquid line drier was also blocked as I had a low suction pressure. Replaced the drier and thermostat, defrosted the evaporator but its still icing up. Checked the heaters and they draw 3.2 amps each, any ideas what would cause this.

Your suction pressure will always be low when the evap is iced up/airflow blocked, as there is insufficient heat to absorb.
Similar symptoms on air conditioning units when the indoor coil is iced, dirty or filters blocked, leading to an incorrect diagnosis of SOG.