Compressors Iced up

[Jad Zeitouni]

Hello,

A cold room is designed to lower the temperature of tortilla bread from 0deg to below - 20deg
It is made of 4 cooling units (copeland compressors) of 10HP with Frigabohn evaporators ( I chose a slightly bigger evaporators to reach a lower temperature - 26deg (bakery storage specifications)) the system is build to freeze more than 8 tons of tortilla bread in around 24hrs.

The system worked well for two weeks before problems started to arise , The compressors started to ice up randomly as well as the evaporators
I put the cooling units on manual defrost several times but in each time one or two of the compressor started cooling cycle before defrost ends (45min defrost time)
I checked the defrost settings and all was electric defrost
Checked the valves and everything was okay

temperature setpoint is -27deg

during the problem the room was not fully loaded ( 4 tons and below)

Could the problem be because the room is not loaded as designed and the temperature is dropping quickly due to the high cooling capacity ?

should I turn off two compressors when the room is not fully loaded ( 8 tons)?

Can anyone please suggest a solution?

Thank you,

[mbc]

1)it is better you put one defrosting timer for all system when you are designing blast freezer .


2) when you were not fully loaded running with 2 or 4 compressor only will effect your pull down times not any thing
check you expansion valve and position of bulb and cover it to sense more actual temp in suction line

[Jad Zeitouni]

1)it is better you put one defrosting timer for all system when you are designing blast freezer .

The defrosting is related to two factors the timing and the evaporator temperature probe . Timing is fixed But the temperature of the probe can differ from one evaporator to another and thus cutting the defrost resulting in different defrost time for the four systems

If I want to keep four control panels is there a way to make one defrost cycle for all four compressors ?

[mbc]

in blast freezer mainly defrosting time should be time when we want to load or unload the room .
we save time and money in this case.
when in one room you want to cool it and in the same time you want to defrost the other system .in cooling system you circulate cold air and it effect the evaporator you want to heat it for defrost and you loos your cool air and also you loos your heat
in blast freezer you know amount of circulation air about 5 times of normal rooms,