York D2CG300 Cooling System, Preliminary Operation Cooling, Cooling Sequence Of Operation

530.18-N11Y

OPERATION

COOLING SYSTEM

The cooling section is a complete factory package utilizing an air-cooled condenser. The system is factory-charged with Refrigerant-22.

The compressors are hermetically sealed, internally sprung and base-mounted with rubber-insulated hold-down bolts.

Compressors have inherent (internal) protection. If there is an abnormal temperature rise in a compressor, the protector will open to shut down the compressor.

PRELIMINARY OPERATION COOLING

After the initial installation, the compressors should be given three false starts (energized just long enough to make a few revolutions) with 5-7 minutes delay between each start, before being put into full time service.

COOLING SEQUENCE OF OPERATION

NO OUTDOOR AIR OPTIONS - When the room thermostat calls for “first-stage” cooling, the low voltage control circuit from “R” to “G” and “Y1" is completed to energize compressors #1/2 (50% capacity), condenser fan motor #1, and the supply air blower motor (if the fan switch on the room thermostat is set in the ”AUTO" position).

When the thermostat calls for “second-stage” cooling, the low voltage control circuit from “R” to “Y2" is completed to energize compressor #3/4.

After the thermostat is satisfied and opens, all components will stop simultaneously. The blower motor will continue to operate if the fan switch on the room thermostat is set in the “ON” position.

ECONOMIZER WITH SINGLE ENTHALPY SENSOR - When the room thermostat calls for “first-stage” cooling, the low voltage control circuit from “R” to “G” and “Y1" is completed. The ”R" to “G” circuit 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 controller (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 compressors #1/2, and condenser fan motor #1.

When the thermostat calls for “second-stage” cooling, the low voltage control circuit from “R” to “Y2" is completed. If the enthalpy of the outdoor air is below the setpoint of the enthalpy controller (i.e. first stage has energized the economizer), ”Y2" will energize compressors #1/2. If the outdoor air is above the setpoint, “Y2" will energize compressor #3/4.

After the thermostat is satisfied and opens, all components will stop simultaneously. The blower motor will continue to operate if the fan switch on the room thermostat is set in the “ON” position.

ECONOMIZER WITH DUAL ENTHALPY SENSORS - The operation with the dual enthalpy sensors is identical to the single sensor except that a second enthalpy sensor is mounted in the return air. This return air sensor 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 whenever the economizer is chosen by the enthalpy sensor for first stage cooling, “Y1". 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 damper motor adjustment. When the “R” to “G” circuit is opened, the damper spring returns fully closed.

CONTINUOUS BLOWER - Continuous blower operation is possible by closing the R to G circuit on the thermostat.

SAFETY CONTROLS

Each refrigerant system is equipped with the following safety controls:

1.A Suction Line Freezestat to protect against low evaporator

temperatures due to a low air flow or a low return air temperature. (Opens at 26° F + 5° F and resets at 38° F + 5° F)

2.A High Pressure Cutout Switch to protect against excessive discharge pressures due to a blocked condenser coil or a condenser motor failure.(Opens at 380 psig + 10 and resets at 300 psig +10)

3.A Low Pressure Switch/Loss Of Charge to protect against loss of refrigerant charge. (Opens at 7 psig + 3 and resets at 22 psig + 5)

If either one of the above safety controls opens, that individual refrigerant system will be locked out. The other refrigerant system will continue in operation unless it too is effected by the same fault. The lock out of either system can be reset by opening the 24V circuit either at the room thermostat or at the unit disconnect.

ELECTRIC HEATING - SEQUENCE OF OPERATION

WITH POWER TO UNIT AND THERMOSTAT IN THE HEATING MODE

Single-stage heating: (applies only to 18 KW heater, all other heaters MUST use a two-stage thermostat:)

a)If the fan switch is in the “ON” position, the evaporator blower motor contactor (3M) will be energized through terminal G to provide continuous blower operation. If the fan switch is in the “AUTO” position, the blower will operate only when there is a call for heating by the thermostat.

NOTE: All 240 & 480V heaters are provided with manual reset backup protection limits. These will de-ener- gize the heaters should the primary limit fail to open or the contactors fail to open in a failure mode.

b)Upon a call for heat by the thermostat, the heater contactor (6M) will be energized.

c)The thermostat will cycle the electric heat to satisfy the heating requirements of the conditioned space.

Two-stage heating: (applies to all heaters except 18 KW):

a)If the fan switch is in the “ON” position, the evaporator blower motor contactor (3M) will be energized through terminal G to provide continuous blower operation. If the fan

Unitary Products Group 15