14
ComPac 9/04-12
the dehumidification mode, the call for cooling will override the call for dehumidification and
the strip heat is disengaged until the thermostat is satisfied. This assures the environment
temperature is maintained as first priority and humidity control is second.
In applications where a shelter has redundant air conditioning units and is controlled by a lead
lag controller (Marvair's LL357D2 or CommStat3™ Controller), most times the dehumidi-
fication option is only necessary on one of the two units. It is possible for one unit to be
operating in the cooling mode while the unit with dehumidification is operating at the same time.
If the cooling unit does not maintain the shelter temperature set point, the unit with
dehumidification will go into the cooling mode. It does not matter whether the unit with
dehumidification is the lead or lag unit.
Three Phase Voltage Monitor, Marvair® P/N 51394
Continuously measures the voltage of each of the three phases. The monitor separately senses
low and high voltage, voltage unbalance including phase loss and phase reversal. An LED
indicator glows when all voltages are acceptable. Automatically resets when voltages and
phases are within operating tolerances.
Dirty Filter Indicators
Two types of dirty filter indicators are available from Marvair
®
. A flag type detects a reduction
of air flow on the discharge side of the filter. When a reduction in air flow is detected, a signal
is sent to a set of dry contacts. For more reliable, precise indication of a dirty filter, a diaphem
type of indicator should be used. This type measures the air pressure on either side of the filter
and when the pressure drops below the set point, a signal is sent to a set of dry contacts. The
set point is adjustable.
Minimum Potential Potentiometer
Used in the ComPac
®
II units with the factory installed economizer. The potentiometer
prevents the economizer from closing completely, assuring that outside air will be brought into
the shelter and exhausted whenever the indoor blower is operating. This provides position
pressurization of the building. The minimum potential potentiometer is adjustable.
The compressor and condenser fan are energized with a contactor controlled by a 24 VAC
pilot signal.
Some compressors incorporate an internal PTC crankcase heater that functions as long as
primary power is available. The heater drives liquid refrigerant from the crankcase and
prevents loss of lubrication caused by oil dilution. Power must be applied to the unit for 24
hours before starting the compressor.
The condenser (outside fan) motor is energized by the same contactor. However, the motor
is cycled on and off by the low ambient control (see low ambient control 1.6a and 1.6b).
The indoor evaporator fan motor is cycled by the blower timed delay relay.
1.8 E
LECTRICAL
D
IAGRAMS
