Page 28 - IOM / Rooftop Smart and Linéa™ Range
THERMOSTAT OPERATION
Some heat pump thermostats incorporate isolating contacts
and an emergency heat function (which includes an amber
indicating light). This feature is applicable to some systems
using auxiliary electric heat.
When the room thermostat is placed in the emergency heat
position, the compressor is locked-out and heating is
provided entirely by the auxiliary electric heat. An amber
indicating light simultaneously comes on to remind the user
that the system switch is operating in the emergency
heat mode.
Emergency heat is usually used during a heat pump
shutdown, but it should also be used following a power
outage if power has been off for over an hour and the outdoor
temperature is below 10°C. System should be left in
emergency heat mode at least six hours to allow the the
crankcase heater (if applicable) sufficient time to prevent
compressor slugging.
COMPRESSOR CONTROLS
High Pressure Switch
The compressor circuit is protected by a high pressure switch
which opens at 28,27 bar and is manually reset.
Crankcase Heaters
SCA/SHA three phase units are equipped with a self
regulating crankcase heater which must be energized at all
times to prevent compressor damage due to refrigerant
migration.
Freezestat (Commercial Units Only)
Commercial models are equipped with a freezestat which
prevents compressor operation if the indoor coil temperature
drops below -2°C+1.6 and automatically resets at 14°C + 2.
Defrost System
The defrost cycle is temperature-initiated and time/pressure-
terminated.
Defrost Control
This control asks for defrost every 90 minutes, and if the
defrost thermostat senses temperatures below (2°C) the unit
will defrost. The defrost control can be field adjusted from a
90 minute to either a 60 minute or 30 minute interval if
warranted by climatic conditions. Defrost cycle will be
terminated when the defrost pressure switch senses
pressures above 19 bar. The control will not allow a defrost
to last for more than 14 minutes.
Defrost Thermostat
The defrost thermostat is mounted on line between the
outdoor distributor and check valve/drier. The unit will not
defrost unless this thermostat senses the line to be 2°C or
colder.
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