Bryant 542J, 548F, 549B manual CONTROLS cont

CONTROLS (cont)

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 (542J150) or com- pressor no. 2 (542J180) and indoor and outdoor fan motors start. If the 5-minute CTD on the DB is satisfied, then compres- sor no. 1 contactor is energized and compressor no. 1 will start.

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 EconoMi$er — With unit main power on, set thermostat at HEAT position and desired room temperature. 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 no. 2 (542J180) and indoor and outdoor fan motors start. If the 5-minute CTD on the DB is satisfied, then compressor (542J150) or compressor no. 1 (542J180) contactor is energized and compressor (542J150) or compressor no. 1 (542J180) will start. The outdoor-air damper stays at vent position while the indoor fan is operating.

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 outdoor- fan motor will stop.

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 10-minute defrost cycle.

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.

Automatic Changeover — When the system selection switch is set at AUTO. position, unit automatically changes from heat- ing operation to cooling operation when the temperature of the conditioned space rises to the cooling level setting. When the temperature of the conditioned space falls to the heating level setting, unit automatically changes from cooling to heating operation (with a 3 F deadband in between).

Continuous Air Circulation — Turn unit power on. Set system control at OFF position. Set fan switch at ON position. The indoor-fan contactor is energized through the thermostat switch and the indoor fan runs continuously.

Cycle-LOC™ Protection — If unit operation is interrupted by an open high-pressure switch, low-pressure switch, indoor coil freezestat, or by compressor internal line-break device (over- current or overtemperature), and compressor is calling for either cooling or heating, Cycle-LOC protection device simultaneously locks out unit and lights a warning light on the thermostat. Restart the unit by manually turning thermostat to OFF and then to ON position. If any of the protective devices opens again, the unit continues to lock out until corrective action is taken.

NOTE: If the unit fails to operate due to compressor over- current 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 Cycle-LOC device locks out the compressor and lights a warning light on the room thermostat. When the switch is on (thermostat is set to the EM HT position), compressor circuit and outdoor thermostats are bypassed, and the second stage of thermostat energizes the indoor blower and the electric resistance heaters.

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