Product manual
13
ComPac 6/09-18
electric reheat operate to temper the air and lower the humidity. If the temperature in the controlled
environment rises above the set point of the thermostat and the unit is operating in the dehumidication
mode, the call for cooling will override the call for dehumidication and the strip heat is disengaged
until the thermostat is satised. This assures the environment temperature is maintained as rst 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 LL357D4 or CommStat3™ Controller), most times the dehumidication 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 dehumidication is operating at the same time. If the cooling unit does not maintain
the shelter temperature set point, the unit with dehumidication will go into the cooling mode. It does
not matter whether the unit with dehumidication is the lead or lag unit.
Three Phase Voltage Monitor, Marvair®
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
A diaphragm type of indicator measures the air pressure on either side of the lter and when the pressure
drops below the set point, an LED is illuminated.
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 ex-
hausted whenever the indoor blower is operating. This prevents negative pressurization of the building.
The minimum potential potentiometer is adjustable.
1.8 eleCTriCal DiaGraMs
The compressor and condenser fan are energized with a contactor controlled by a 24 VAC pilot sig-
nal.
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 1.6).
The indoor evaporator fan motor is controlled by the fan purge on the electronic control board.