Sunlife Enterprises DM300 Sequence Of Operations Overview, Cooling Sequence Of Operation

356214-XIM-A-0108

OPERATION

SEQUENCE OF OPERATIONS OVERVIEW

For these units, the thermostat makes a circuit between "R" and "Y1" for the first stage of cooling.

The call is passed to the unit control board (UCB), which then determines whether the requested opera- tion is available and, if so, which components to ener- gize.

For gas heating, the UCB monitors the "W1" call but does not handle the operation of the gas furnace. An ignition control board controls the gas heater operation.

For electric heat units, the UCB passes the call to the electric heater.

In both cases, when the "W1" call is sensed, the indoor air blower is energized following a specified heating delay.

If at any time a call for both heating and cooling are present, the heating operation will be performed. If operating, the cooling system is halted as with a com- pletion of a call for cooling. Heating always takes prior- ity.

COOLING SEQUENCE OF OPERATION

CONTINUOUS BLOWER

By setting the room thermostat fan switch to "ON," the supply air blower will operate continuously.

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 the first stage of cooling, the low-voltage control circuit from "R" to "Y1" and "G" is completed. For first stage cooling, compressor #1,

condenser fan motor #1, and condenser fan motor #2 for 15 and 20T only (if the ambient temperature is above 60°F), are energized. After completing the spec- ified fan on delay for cooling, the UCB will energize the blower motor.

When the thermostat calls for the second stage of cool- ing, the low-voltage control circuit from "R" to "Y2" is completed. Compressor #2, and condenser fan motor #2, 25T only (if the ambient temperature is above 60°F), is energized, provided it has not been locked- out.

If there is an initial call for both stages of cooling, the UCB will delay energizing compressor #2 by 30 sec- onds in order to avoid a power in rush.

Once the thermostat has been satisfied, it will de-ener- gize Y1 and Y2. If the compressors have satisfied their minimum run times, the compressors and condenser fans are de-energized. Otherwise, the unit operates each cooling system until the minimum run times for the compressors have been completed. Upon the final compressor de-energizing, the blower is stopped fol- lowing the elapse of the fan off delay for cooling.

To be available, a compressor must not be locked-out due to a high or low-pressure switch or freezestat trip and the anti-short cycle delay (ASCD) must have elapsed.

ECONOMIZER WITH SINGLE ENTHALPY SENSOR -

When the room thermostat calls for "first-stage" cool- ing, the low voltage control circuit from "R" to "G" and "Y1" is completed. The UCB energizes the blower motor (if the fan switch on the room thermostat is set in the "AUTO" position) and drives the economizer damp- ers from fully closed to their minimum position. If the enthalpy of the outdoor air is below the setpoint of the enthalpy controller (previously determined), "Y1" ener- gizes the economizer. The dampers will modulate to maintain a constant supply air temperature as moni- tored by the discharge air sensor. If the outdoor air enthalpy is above the setpoint, "Y1" energizes com- pressor #1, condenser fan motor #1, and condenser fan motor #2, 15 and 20T only (if the ambient tempera- ture is above 60°F).

When the thermostat calls for "second-stage" cooling, the low voltage control circuit from "R" to "Y2" is completed. The UCB energizes the first available compressor If the enthalpy of the outdoor air is below the setpoint of the enthalpy controller (i.e. first stage

36 Johnson Controls Unitary Products