CONTROLS (cont)
Continuous Air Circulation — Turn unit power on. Set system control at OFF position. Set fan switch at ON position. The
NOTE: If the unit fails to operate due to compressor overcurrent condition, restart by manually resetting circuit breakers at the unit. Restart cannot be accomplished at the room thermostat.
Emergency Heat — If compressor is inoperative due to a tripped safety device (high or low pressure, indoor coil freez- estat, overcurrent, or overtemperature), the
SEQUENCE OF OPERATION — 542J150,180
Cooling, Units Without Economizer — With unit main power on, set thermostat to COOL position and desired room tempera- ture. Set fan switch at AUTO. (on demand) or ON (continuous) position.
On a rise in room temperature, cooling contactor no. 1 in the thermostat closes. The indoor and outdoor fan motors start. If the
On 542J180 units, with an additional rise in room temperature, cooling contactor no. 2 in the thermostat closes, energizing compressor contactor no. 2. Compressor no. 2 starts and cycles on demand of the thermostat to satisfy the occupied space demands.
On 542J150 units, compressor runs fully loaded on a call for
Cooling, Units With Economizer — Upon a call for cooling, when outdoor ambient temperature is above the temperature control setting, the indoor and outdoor fans and compressor(s) energize. The economizer damper moves to vent position.
Upon a
Upon a
below 50 F, a cooling lockout switch prevents the compressor(s) from running.
When
A freeze protection thermostat (FPT) is located on the indoor coil. It detects frost
Heating, Units Without Economizer — With unit main power on, set thermostat at HEAT position and desired room tempera- ture. Set fan switch at AUTO. (on demand) or ON (continuous) position.
On a drop in room temperature, heating contactor no. 1 in the thermostat closes, energizing heat relay (HR), reversing valve relay (RVR), reversing valve solenoids (RVS1 and RVS2) and compressor no. 2 contactor. Compressor (size 150) or com- pressor no. 2 (size 180) and indoor and outdoor fan motors start. If the
On units equipped with electric heat, when additional heat is needed, heating contactor no. 2 in the thermostat closes, ener- gizing W2.
Heating, Units With Economizer — With unit main power on, set thermostat at HEAT position and desired room temperature. Set fan switch at AUTO. (on demand) or ON (continuous) posi- tion.
On a drop in room temperature, heating contactor no. 1 in the thermostat closes, energizing heat relay (HR), reversing valve relay (RVR), reversing valve solenoids (RVS1 and RVS2) and compressor no. 2 contactor. Compressor no. 2 (size 180) and indoor and outdoor fan motors start. If the
(180)contactor is energized and compressor (542J150) or compressor no. 1 (180) will start. The
On units equipped with electric heat, when additional heat is needed, heating contactor no. 2 in the thermostat closes, ener- gizing W2.
Defrost Cycle — When the temperature of the outdoor coil drops below 28 F as sensed by the defrost thermostat (DFT1 or DFT2), the defrost timer starts. At the end of a timed period (field set at 30, 50, or 90 minutes), the defrost cycle will begin. The defrost board energizes terminals O and W2, energizes the defrost relay (DR), deenergizes the reversing valve solenoids (RVS1 and RVS2), and energizes the electric heat. The
The unit continues to defrost either until the coil temperature as measured by DFT1 or DFT2 reaches 65 F, or until unit com- pletes a
During the defrost mode, when a circuit defrosts, RVS will oscil- late between heating and cooling modes until defrost mode is complete. This will prevent the head pressure from getting too high.
At the end of the defrost cycle, the electric heaters (if applica- ble) will be deenergized, the reversing valve solenoids will be energized, and the outdoor fans will start.
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