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SXIH-SVX01B-EN 21
Operation
Sequence of
Operation
Sequence of Operation
The thermostat controls the unit
operation. It has both manual and
automatic switches so the thermostat
maintains desired comfort levels.
The fan switch allows manual selection of
the fan speed using the On or Auto
setting. With the switch set in the On
position, the evaporator fan runs continu-
ously, independent from the thermostat
temperature setting. The Auto position
cycles the evaporator fan on and off with
the demand for heating or cooling.
The system switch may have two or
more positions. For example, using a
cooling only thermostat, the system
switch can be set in the Off or the Cool
position. The Off position disconnects
power from the thermostat contacts that
control the condensing unit. This prevents
the condensing unit from running,
regardless of the thermostat tempera-
ture setting. The evaporator fan may
circulate air if the fan switch is in the On
position. With the switch in the Cool
position the condensing unit and evapo-
rator will operate on a signal from the
thermostat calling for cooling.
With the fan switch set to Auto and the
system switch set to Cool, the following
sequence takes place. On a rise in room
temperature, the thermostat contacts
close to provide power to the evaporator
fan contactor, the condensing unit fan
contactor, and the condensing unit
compressor contactors. As the room
temperature reaches setpoint, the
thermostat contacts open to de-energize
all contactors, and the system cycles off.
This system will remain off until additional
cooling is required and the cycle repeats.
Table OS-O-1. Normal Operating Conditions
high pressure 200 to 340 psig
low pressure 54 to 80 psig
superheat 8 to 12
o
C
subcooling 5 to 10
o
C
liquid sightglass refrigeration flow with no gas traces
current must not surpass the rated current
Table O-OS-2. Controls Adjustment
Control Disarming Rearming
High pressure control 395 +/- 15 psig 280 +/- 20 psig
Low pressure control 25 +/- 8 psig 80 +/- 12 psig
Limit low pressure control 10 +/-3 psig 35 +/-5 psig
Motor windings thermostat 105
o
C82
o
C