Manitowoc Ice QM20 Ice Machine Operation, Sequence of Operation, Refrigeration System Start-Up

Section 3	Ice Machine Operation
	Section 3
	Ice Machine Operation

Sequence of Operation

	Ice Making		Control Board Relays
		1	2	3	Length of
	Sequence of	Compressor	Hot Gas Valve	Water Pump
					“ON” Time
	Operation		Water Fill Valve	Fan Motor
Start-Up1		Off	On	Off	2.9 Minutes
1.	Water Purge				(175 Seconds)
2.	Refrigeration	On	On	Off	5 Seconds
	System Start-Up
3.	Freeze Cycle	On	Off	On	Automatically
					determined
4.	Harvest Cycle	On	On	Off	Automatically
					determined
5.	Auto Shut-Off	Off	Off	Off	Until bin thermostat
					re-closes

1Initial Start-Up or Start-Up After Automatic Shut-Off

INITIAL START-UP OR START-UP AFTER AUTOMATIC SHUT-OFF

1. Water Purge

The water fill valve and the hot gas valve are energized for 2.9 minutes (175 seconds). This ensures that the ice making cycle starts with fresh water, and that the refrigerant pressures are equalized prior to refrigeration system start-up.

2. Refrigeration System Start-Up

The compressor starts 2.9 minutes (175 seconds) after the water fill valve and hot gas valve are energized. (The water fill valve and hot gas valve remain energized for 5 seconds during compressor start-up, and then shut off.) The compressor remains on throughout the entire freeze and harvest cycles.

3. FREEZE CYCLE

The condenser fan motor and water pump are energized and remain on throughout the entire freeze cycle. An even flow of water is directed across the evaporator and into each cube cell, where it freezes.

The control system automatically determines the length of the freeze cycle by monitoring the temperature of the refrigeration system liquid line.

4. HARVEST CYCLE

The condenser fan motor and water pump de- energize. The water fill valve energizes to purge the water in the water trough. The hot gas valve also energizes at the beginning of the harvest cycle to divert hot refrigerant gas into the evaporator. The hot refrigerant gas warms the evaporator, causing the cubes to slide, as a sheet, off the evaporator and into the ice storage bin.

The control system automatically determines the length of the harvest cycle, based on the temperature of the refrigeration system liquid line at the end of the freeze cycle. At the end of the harvest cycle, the ice machine returns to another freeze cycle (step 3, above).

5. AUTOMATIC SHUT-OFF

The ice machine shut-off is controlled by the level of ice in the ice storage bin. When the bin is full, ice cubes contact the bin thermostat bulb holder, which cools down and opens to stop the ice machine. The ice machine remains off until enough ice has been removed from the bin. This causes the thermostat bulb holder to warm and close, restarting the ice machine. When the ice machine restarts, it returns to the start-up sequence (steps 1 and 2, above).

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