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Controls, Operating sequence – Carrier 50XP User Manual

Page 22

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22

CONTROLS

Operating sequence

Cooling — When the system thermostat calls for cooling, 24 V is
supplied to the “Y” and “G” terminals of the thermostat. This

completes the circuit to the contactor coil (C) and indoor fan
board. The normally open contacts of C close and complete the

circuit to compressor motor (COMP) and to outdoor (condenser)

fan motor (OFM). Both motors start instantly. The IFM starts
according to the selection pin set--up on the Easy Select Board.
On the loss of the thermostat call for cooling, 24 V is removed
from both the “Y” and “G” terminals (provided the fan switch is in

the “AUTO” position) de--energizing the compressor contactor and

opening the contacts supplying power to compressor/OFM. After a
preselected delay, the IFM shuts off. If the thermostat fan selector

switch is in the “ON” position, the IFM will run continuously at
speed selected on Easy Select Board

Heating — If accessory electric heaters are installed, on a call for
heat, circuit R--W is made through the thermostat contacts. Circuit

R--G is made which energizes the IFM. If the heaters are staged,
then the thermostat closes a second set of contacts (W2) when

second stage is required. When thermostat is satisfied, contacts

open, deenergizing the heater relay. After a preselected delay, the
IFM shuts off. If the thermostat fan selector switch is in the “ON”

position, the IFM will run continuously at speed selected on Easy
Select Board.
NOTE: On units with a Time Guard

®

II device: Once the

compressor has started and then stopped, it cannot be restarted
again until 5 minutes have elapsed.
The indoor blower operation with a call for fan operation (G) in
cooling mode will perform by the on/off delay profile selected at

start up on the Easy Select Board.

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