INTERMITTENT BLOWER
With the room thermostat fan switch set to “AUTO” and the system switch set to either the “AUTO” or “HEAT” settings, the blower is energized whenever a cooling or heating operation is requested. The blower is ener- gized after any specified delay associated with the operation.
When energized, the indoor blower has a minimum run time of 30 seconds. Additionally, the indoor blower has a delay of 10 seconds between operations.
NO OUTDOOR AIR OPTIONS
When the thermostat calls for cooling, the
Once the thermostat has been satisfied, it will
To be available, a compressor must not be
ECONOMIZER WITH SINGLE ENTHALPY SENSOR -
When the room thermostat calls for cooling, the low voltage control circuit from “R” to “G” and “Y1” is com- pleted. The UCB energizes the blower motor (if the fan switch on the room thermostat is set in the “AUTO” position) and drives the economizer dampers from fully closed to their minimum position. If the enthalpy of the outdoor air is below the setpoint of the enthalpy con- troller (previously determined), “Y1” energizes the economizer. The dampers will modulate to maintain a constant supply air temperature as monitored by the discharge air sensor. If the outdoor air enthalpy is above the setpoint, “Y1” energizes the compressor and condenser fan motor only.
Once the thermostat has been satisfied, it will
energized. Otherwise, the unit operates the cooling system until the minimum run times for the compressor has been completed. After the compressor
ECONOMIZER WITH DUAL ENTHALPY SENSORS -
The operation with the dual enthalpy sensors is identi- cal to the single sensor except that a second enthalpy sensor is mounted in the return air. This return air sen- sor allows the economizer to choose between outdoor air and return air, whichever has the lowest enthalpy value, to provide maximum operating efficiency.
ECONOMIZER (SINGLE OR DUAL) WITH POWER EXHAUST -
This system operates as specified above with one addition. The power exhaust motor is energized 45 seconds after the actuator position exceeds the exhaust fan setpoint on the economizer control. When the power exhaust is operating, the second stage of mechanical cooling will not operate. As always, the “R” to “G” connection provides minimum position but does not provide power exhaust operation.
MOTORIZED OUTDOOR AIR DAMPERS -
This system operation is the same as the units with no outdoor air options with one exception. When the “R” to “G” circuit is complete, the motorized damper drives open to a position set by the thumbwheel on the damper motor. When the “R” to “G” circuit is opened, the damper spring returns fully closed.
COOLING OPERATION ERRORS
Each cooling system is monitored for operation outside of the intended parameters. Errors are handled as described below. All system errors override minimum run times for compressors.
HIGH-PRESSURE LIMIT SWITCH
During cooling operation, if a
28 | Unitary Products Group |