035-17233-000-C-0702

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 installation has been completed, energize the crank- case heaters for at least four hours before operating the unit. 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.

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, condenser fan motor #1, condenser fan motor #2 (if the ambient temperature is above 60F), 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 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 compressor #1, condenser fan motor #1, and condenser fan motor #2 (if the ambient temperature is above 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 econo- mizer), Y2 will energize compressor #1. If the outdoor air is above the setpoint, Y2 will energize compressor #2.

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 maxi- mum 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 econo- mizer 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 out- door 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.

CONTINUOUS BLOWER

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

SAFETY CONTROLS

1.A Suction Line Freezestat to protect against low evapo- rator 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 exces- sive discharge pressures due to a blocked condenser coil or a condenser motor failure. (Opens at 380 psig + 10 and resets at 300 psig +10)

Unitary Products

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Energy Tech Laboratories DHG180, DHG240 Cooling System, Preliminary Operation Cooling, Cooling Sequence of Operation
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DHG180, DHG240 specifications

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