40
Marvair MAA/MGA Wall Mount AC Installation & Operation Manual
05/2023 Rev.21
3.8 Electrical Connections
WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow safety warnings exactly could result in serious injury, death, and/or
property damage.
Turn off electrical power at fuse box or service panel BEFORE making any electrical
connections and ensure a proper ground connection is made before connecting line
voltage.
Important
All electrical work must meet the requirements of local codes and ordinances.
Work should be
done
only
by qualified persons.
Units may incorporate an internal crankcase heater for compressor protection.
The crankcase heater
must be energized for at least 24 hours prior to starting the compressor.
Scroll compressors, like several other types of compressors, will only compress in one rotational direction.
The direction of rotation is not an issue with single-phase compressors since they will always start and
run in the proper direction. However, three phase compressors will rotate in either direction depending
upon phasing of power. Since there is a 50-50 chance of connecting power in such a way as to cause
rotation in the reverse direction, it is imperative to confirm that the compressor is rotating in the proper
direction at the initial field start-up of the system. Verification of proper rotation is made by observing
that the suction pressure drops and the discharge pressure rises when the compressor is energized. An
alternate method of verification for self contained system with small critical refrigerant charges, where
the installation of gauges may be objectionable, can be made by monitoring the temperature of the
refrigerant lines at the compressor. The temperature should rise on the discharge line while the suction
line temperature decreases. Reverse rotation also results in a substantially reduced current draw when
compared to tabulated values.
There is no negative impact on durability caused by operating three phase compressors in the reversed
direction for a short duration of time, usually defined as less than one hour. However, after several
minutes of operation the compressor's internal protector will trip. The compressor will then cycle on
the protector until the phasing is corrected. Reverse operation for longer than one hour may have a
negative impact on the bearings.
To change the rotation, turn off power to the unit and reverse L1 & L2 at the disconnect in the air
conditioner.
High Voltage Wiring - (Single Units)
The power supply should have the proper voltage, phase, and ampacity for the selected model.
1. Refer to the electrical data on the data sticker on the unit for field wiring requirements of the unit.
Size the incoming power supply lines and the fuse(s) or HACR breaker(s) according to requirements
described in the National Electric Code. Run the power conductors through the knockouts on the
side or back of the unit. Use appropriate conduit and strain reliefs.
