York B2CH180 Cooling System, Preliminary Operation, Cooling Sequence of Operation

035-18895-000-A-0902

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.

The compressors also have inherent (internal) protection. If there is an abnormal temperature rise in a compressor, the protector opens to shut down the compressor.

PRELIMINARY OPERATION

After installation has been completed, energize the crankcase heaters for at least four hours before operating unit. After this initial warm-up, 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.

NOTE: Prior to each cooling season, the crankcase heaters must be energized at least 8 hours before system is put into operation.

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 compressor #1, outdoor fan motor #1, outdoor fan motor #2 (if the ambient temperature is above 16°C (60°F)), 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 #2.

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

The reversing valve is energized thru the “Y1” circuit when the subbase is in the cooling mode.

The suction line freezestat cuts the compressors out when the suction line temperature drops below -3°C (26°F). This is an automatic reset device.

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 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 compressor #1, outdoor fan motor #1, and outdoor fan motor #2 (if the ambient temperature is above 16°C (60°F)).

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” energizes compressor #1. If the outdoor air is above the setpoint, “Y2” energizes compressor #2.

After the thermostat is satisfied and opens, all components stop simultaneously. The blower motor continues 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 thumbwheel on the damper motor. When the “R” to “G” circuit is opened, the damper spring returns fully closed.

HEATING SEQUENCE OF OPERATION

The following sequence of operation is based on using a standard heat pump two-stage heating/two-stage cooling thermostat/subbase. Economizer (if supplied) operation is not allowed in the heating mode; however, the minimum position does operate.

FIRST STAGE HEAT

When the thermostat calls for “heating”, the low voltage control circuit from “R” to “G”and “W1” (wiring schematic) is completed to energize the compressors, outdoor fan motors and blower motor (if subbase is set on auto) simultaneously. If the subbase has the indoor fan set on “on” the motor will run all of the time.

SECOND STAGE HEAT

If the compressors alone can not satisfy the heating requirements, second stage heat energizes all the electric heat (if supplied) thru the “W2” circuit.

12 Unitary Products Group