Emerson 3000/ITR Manuale Utente

On water-cooled and glycol-cooled digital scroll units, the discharge pressure is controlled by a motor-

ized ball valve. During unloaded operation, the pressure changes during each digital cycle could 

result in excessive repositions with a pressure operated water regulating valve. The control algorithm 

for the motorized ball valve uses an intelligent sampling rate and adjustable pressure thresholds to 

reduce valve repositions. The valve assembly consists of the brass valve, linkage and actuator.

The valve actuator operates on 24VAC power and is controlled by a 2-10VDC proportional control sig-

nal. The valve full open to full close time is 60 seconds. At 2VDC the valve is closed; at 10VDC the 

valve is fully open. There is a 20-second delay to position the motorized ball valve before starting the 

compressor.

The control utilizes an upper and lower pressure threshold with a 35 PSI (241 kPa) deadband to 

reduce valve movement. If the liquid pressure is between the upper and lower threshold the valve 

remains at the current position. If the liquid pressure exceeds the upper threshold the valve opens, 

and if the pressure falls below the lower threshold the valve closes. There are multiple adjustment bands to 
ease discharge pressure back into control range.

Both pressure thresholds can be shifted simultaneously over a 50 PSI (345 kPa) range (the 35 PSI 

[241 kPa] differential remains constant). The ball valve setpoint offset parameter in the Service menu 

can be adjusted from 0 to 50 PSI (345 kPa) to raise or lower the control band similar to the pressure 

adjustment on a water regulating valve. Units are factory set at a 30 PSI (207 kPa) setpoint offset (30 

PSI [207 kPa] above minimum). This results in a 220 PSIA (1517 kPa) lower threshold and a 255 

PSIA (1758 kPa) upper threshold pressure.

The setpoint offset is adjusted to the minimum value during startup, then transitions to the set value 

once the compressor reaches normal operating pressures. Additionally changes in fluid temperature 

could cause pressure changes that do not result in valve movement within the dead band on drycool-

ers. Fan cycling stats should be set to prevent continuous fluid temperature swings greater than 10

o

F 

(5.6

o

C) (see 7.4.10 - Drycooler Settings).

The motorized ball valves are located in the condenser fluid return line. The three-way valve is piped 

in a mixing arrangement with the common port at the valve outlet.

The valve can be manually set by disconnecting AC power, depressing the manual override button on 

the valve actuator, and adjusting the valve position with the handle. You also have the option to con-

trol the motorized ball valves through the Service menu using manual mode to override the normal 

control.

The water regulating valve automatically regulates the amount of fluid necessary to remove the heat 

from the refrigeration system, permitting more fluid to flow when load conditions are high and less 

fluid to flow when load conditions are low. The valve consists of a brass body, balance spring, valve 

seat, valve disc holders, capillary tube to discharge pressure, and adjusting screw.

Adjustment—The valve may be adjusted with a standard refrigeration service valve wrench or 

screw driver. Refer to Table 7 for recommended refrigerant pressures.
To lower the head pressure setting, turn the square adjusting screw clockwise until the high pressure 

gauge indicates the desired setting.