26
SXIH-SVX01C-EN
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 continuously, 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 temperature 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 evaporator 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 9.
Normal operating conditions (SCIH / SCIJ)
high pressure
200 to 340 psig (SCIH) / 320 to 570 psig (SCIJ)
low pressure
54 to 80 psig (SCIH) / 100 to 160 psig (SCIJ)
superheat
8 to 12°F (SCIH) / 4 to 9°F (SCIJ)
subcooling
5 to 10°F
liquid sightglass
refrigeration flow with no gas traces
current
must not surpass the rated current
Table 10. Controls adjustment (SCIH / SCIJ)
Control
Disarming
Rearming
High pressure control
395 ± 15 psig (SCIH) / 609 ± 17 psig (SCIJ) 280 ± 20 psig (SCIH) / 479 ± 29 psig (SCIJ)
Low pressure control
25 ± 8 psig (SCIH) / 51 ± 7 psig (SCIJ)
80 ± 12 psig (SCIH) / 94 ± 7 psig (SCIJ)
Motor windings thermostat
221 ± 5°F
180 ± 5°F
