10
Marvair Wall Mount Heat Pump I&O Manual
06/2023 Rev.7
1.6 Options
Low Ambient Control
The low ambient control permits mechanical cooling when outdoor ambient temperatures are low. The
control uses a reverse-acting high pressure switch to cycle the condenser fan motor according to liquid
refrigerant pressure conditions. Switch closure and fan operation occurs when the pressure reaches 400
PSIG. The switch opens again when the refrigerant pressure falls to 245 PSIG. Therefore, the outdoor
fan always starts after the compressor,
and it will cycle frequently during normal operation at low
outdoor conditions.
Hard Start Kit
Used on single phase equipment to give the compressor higher starting torque under low voltage conditions.
Field installed only. (Not generally recommended for use on scroll compressor.)
Adjustable Outdoor Thermostat
Will not allow electric resistance heat to be energized unless the outdoor temperature is below the desired
set point. Field or factory installed. Available on all Marvair units. P/N 93934
Single Point Feed
When multiple internal disconnects are used, single point feed permits only one field power supply to
heat pump. Field installed only. Available on all Marvair H/P units.
Energy Management System (EMS)
Relay to control the heat pump. Available in 24, 120 or 240 VAC. Field or factory installed.
Electric Reheat for Dehumidification
Control provides simultaneous operation of compressor when in cooling mode and the electric elements
to provide dehumidification without over cooling the room. The electric element (kW) must be properly
sized for each model for proper operation. Factory installed. Available on all MAA units. Consult factory
for details.
Hot Gas Reheat (HGR)
Marvair
®
heat pumps equipped with the Hot Gas Reheat (HGR) allow the indoor humidity of the controlled
environment to be maintained at or below a certain humidity set point. These units do not have the ability
to add humidity to the classroom.
Dehumidification is achieved by operating mechanical cooling in conjunction with a hot gas reheat coil.
The coil is sized approximately to the sensible capacity of the total tonnage of the machine.
Speed Control for GreenWheel
®
ERV Exhaust Blower
For separate control of the exhaust blower. When used, the standard speed controller operates the intake
blower and the optional second controller the exhaust blower. Individual blower control allows positive
pressurization of the classroom. Can be factory or field installed.
