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Marvair Classic AVPA/HVPA/HVPSA Heat Pump I&O Manual
11/2017 Rev. 7
heater contactor(s) which powers all the heating elements. This single function thermal cut-out switch
operates totally independent of the dual thermal cut-out switch described above. If the single function
switch senses an overheat situation, it opens the control circuit and turns off all of the installed heating
elements via the heater contactor(s). Because this switch controls the heater contactor(s), only one switch
is required to disconnect power from the contactor(s), regardless of the number of heater elements. This
single function switch is also non-resettable, and must be replaced by qualified service personnel after
the source of the overheat problem is resolved. This switch would typically open if both elements of the
dual thermal cut-out switches failed.
Electrical Schematics
5.1 Electrical Schematics
The compressor and condenser fan are energized with a contactor controlled by a 24 VAC pilot signal.
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 1.5).
Note:
Only on heat pumps equipped
with an economizer.
The compressor incorporates 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
be oil dilution. Power must be applied to the unit for 24 hours before starting the compressor.
Note:
Heat
pumps with scroll compressors generally do not require crankcase heaters.
The indoor evaporator fan motor is cycled by the blower timed delay relay. See Figure 9. Due to the large
number of variations and options available for the Classic heat pumps, it is not practical to include every
possible wiring schematic in this manual. The following schematics are typical. Included in each heat
pump is the electrical schematic for that unit. Always refer to the schematic in the unit when installing
or servicing the heat pump.
