Sequence of
Operation 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
Table
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
high pressure | 200 to 340 psig |
low pressure | 54 to 80 psig |
superheat | 8 to 12oC |
subcooling | 5 to 10oC |
liquid sightglass | refrigeration flow with no gas traces |
current | must not surpass the rated current |
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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 | 35 |
Motorwindingsthermostat | 105oC | 82oC |
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