The evaporator is frosted

Frosting on the evaporator is a good sign that the compressor is operating, however, if the fridge is still not at optimum temperature, check the rest of the troubleshooting guides such as if the thermostat is working or if the condensing unit is clean and if the compressor is working normally.

Block of ice on the evaporator

A block of ice on the evaporator will prevent heat exchange to occur. Ice is an insulator so this will prevent the fridge from cooling the product or area.

Common causes:

1. Failed Evaporator Fans
If the evaporator fans are not working correctly or are blowing in the wrong direction, this can cause low airflow therefore ice will build up on the evaporator.

2. Dirt or blockage
Dirt on an evaporator will certainly cause ice build-up as it will prevent even airflow through the evaporator coils.

Blockages such as plastic, paper or debris that have been sucked into the system should also be checked.

3. Dirty filters covers
Although commonly found on aircon units, some evaporators for cold rooms have filters which can get clogged.

4. Low refrigerant
Low refrigerant usually causes one side of the evaporator to freeze up, especially the TXV. On domestic units, you will notice that the freezer box is iced, but the fridge compartment may be warm.

5. Blocked drain pipe
On some refrigeration units, there may be a drain pipe and a drip tray under the evaporator. If this is blocked it can cause ice build-up which will continue to grow upwards towards the evaporator coils.

A blocked drain pipe can be caused by a blockage or if the drain heater (where applicable) has failed.

6. Failed defrosting system
If the defrost timer, heating elements or the defrost thermostats fail, this can cause ice to build up rather quickly.

7. Perished door seals
If door seals are in a bad condition, this can cause moisture to enter the system and collect on the evaporator which will result in ice build-up.

8. Excessive opening of the doors
If the unit door is opened frequently this can cause moisture to enter and ice up the evaporator. The same principle applies if the door is left open for long periods. In commercial businesses, this frequently occurs during stock-take when the fridge doors are left open for long periods.

9. Failed TXV
Although not very common, in a situation where the TXV has failed, either the sensing bulb is the cause, the orifice is blocked or the bellows have collapsed. This should be the last resort to change when diagnosing as this repair could be costly. In other circumstances, the regulating screw has been tampered with.