Zamil MAC-240, Installation, Operation & Maintenance Manual

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4. CONTROL SYSTEM
4.1 GENERAL DESCRIPTION:
The ACU section control is managed by a 16-bit microprocessor board fixed in the main control panel with a separate
LCD display as user’s interface. The control board completely controls the operation of the refrigeration system; i.e.,
compressors and condenser fan motors, and the variable frequency drive. The variable frequency drive operates in
coordination with the microprocessor board to control the speed of the supply fan motor. Please refer figure below for the
system flow diagram and I/O signals processed by the microprocessor board.
4.2 COOLING CONTROL
In general, the temperature of the supplied air and the CFM are major factors in cooling control. Temperature sensor
(STS) and differential pressure transmitter (DPS) is fixed at the supply air extender of the fan motor to sense the
temperature and pressure of the supplied air. The signals are transmitted to the microprocessor board which will then
manage the operation of the compressors in the unit.
Cooling or compressor operation can only be able to start if the following conditions are met:
a) Supply air CFM is within 10% of the set CFM (set @ 2200) and air pressure is less than the set maximum supply
air pressure (set @ 21”WG).
b) No alarms or system faults.
c) Supply air temperature is as described in 4.2.1
4.2.1 TEMPERATURE SETTINGS
Cooling operation is active if the supply air temperature is 12 0 C and above. The compressors are stopped when supply
air temperature goes down at 3 0 C and re-starts only when temperature goes up to 12 0 C, provided that this condition is
maintained in a span of 3 minutes.
4.2.2 COOLING MODES
Cooling operation is selectable in three different cooling levels; Low Cool, Medium Cool and High Cool modes. The
temperature settings are fixed and as described in paragraph 4.2.1. Each mode differs only in the compressor run
timings. The compressor run timings can be well described by the following representation: