should have the cutout set at 395 PSIG (27 bar) for R22 and R407C models. The micro will, however, accept values between 200 - 399 PSIG (14 - 28 bar).

To program the Discharge Pressure Cutout, key in the desired value and press the Enter key to store the value into memory and scroll to the next display.

High Discharge Pressure Unload Point

D I S C H A R G E P R E S S U R E U N L O A D = 3 6 0 . 0 P S I G

The Discharge Pressure Unload point is used to avoid a high pressure cutout shutdown by unloading a com- pressor, if its discharge pressure approaches the cutout value. The chiller can then continue to run automatically at reduced capacity until the cause of the excessive pres- sure is attended to (e.g. dirty condenser coils) or ceases naturally (e.g. high ambient temperature).

For the first 60 seconds of operation, discharge pres- sure limiting is disabled. After this time, if discharge pressure exceeds the programmed limit, unloading of the affected compressor will occur until the discharge pressure drops below the programmed limit. The mes- sage will be removed and reloading will take place when discharge pressure has dropped to 90% of the programmed unload point..

Typically the unload point should be set 20 - 25 PSIG (1.4 - 1.7 bar) below the below the discharge pressure cutout setting. The micro will accept a range of program- mable values between 200 - 399 PSIG (14 - 28 bar).

To program the Discharge Pressure Unload, key in the required setting and press the Enter key to store the value into memory and scroll to the next display.

Low Suction Pressure Cutout

S U C T I O N P R E S S U R E

C U T O U T = 4 4 . 0 P S I G

The Low Suction Pressure Cutout protects the evapo- rator from damage due to ice build up caused by op- eration at low refrigerant suction pressure.

FORM 201.19-NM1 (204)

After the compressor starts, and the pump down cycle is completed (pump down to cutout or 30 seconds, which- ever comes first.), suction pressure is monitored as long as the compressor runs. For the first 270 seconds of run- ning, suction pressure can be lower than the programmed cutout, but must be greater than:

Programmed X Run Time/3 + 10

Cutout100

Example: If programmed Cutout = 44 PSIG (3 bar) and Run Time = 60 seconds

 

60/3 + 10

New Cutout = 44 X

100 = 13.2 PSIG (0.9 bar)

This cutout value increases with time, until after 270 sec- onds, it equals the programmed cutout value. If suction pressure falls below the calculated cutout value before 270 seconds, the system will be shut down.

After 270 seconds, a transient timer prevents short term fluctuations in suction pressure from causing shutdown as follows: If suction pressure drops below the cutout point, a 90 second transient timer starts. During the 90 second time period, the suction pressure must be greater than:

Programmed X 100 - transient time remaining

Cutout100

Example: If programmed Cutout = 44 PSIG (3 bar) and the timer has run 30 seconds:

New Cutout = 44 PSIG X 100-60 = 17.6 PSIG (1.2 bar) 100

This cutout value increases with time, until after 90 seconds, it equals the programmed cutout value. If the suction pressure rises to more than 5 PSI (0.3 bar) above the programmed cutout value during the 90 second time period, the timer will be reset. If the suction pressure does not rise to more than 5 PSI (0.3 bar) above the cutout, the timer will remain at zero and if the pressure then falls below the cutout again, the system will shut down on a low pressure fault.

If the Dip Switch on the microprocessor board is set for “Water Cooling” (see Section 3.7), the cutout is programmable between 44 - 70 PSIG (3-5 bar) for both R22 and R-407c models. In this mode, settings of 44 PSIG (3 bar) for R22 and R-407C are recommended. If the Switch is set for “Brine Cooling” (glycol) the cutout is programmable between 5 - 70 PSIG (0.3 bar) for R22 and R-407c models. In this mode, the cutout should be

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