Carrier 48SS manual Controls, Sequence of operation

Controls

Sequence of operation

Heating Ð On a call for heating, terminal ``W'' of the ther- mostat is energized, starting the induced-draft motor. When the hall-effect sensor on the induced-draft motor senses that it has reached the required speed, the burner sequence be- gins. This function is performed by the integrated control board (IGC). The indoor-fan motor is energized 45 seconds after ¯ame is established. When the thermostat is satis®ed and ``W'' is deenergized, the indoor-fan motor stops after a 45-second time-off delay.

Cooling Ð With the room thermostat SYSTEM switch in the COOL position and the FAN switch in the AUTO. po- sition, the cooling sequence of operation is as follows:

When the room temperature rises to a point that is slightly above the cooling control setting of the thermostat, the ther- mostat completes the circuit between thermostat terminal R to terminals Y and G. These completed circuits through the thermostat connect contactor coil (C) (through unit wire

Y)and blower relay coil (BR) (through unit wire G) across the 24-v secondary of transformer (TRAN).

The normally-open contacts of energized contactor (C) close and complete the circuit through compressor motor (COMP) and condenser (outdoor) fan motor (OFM). Both motors start instantly.

The set of normally-open contacts of energized relay BR close and complete the circuit through evaporator blower (indoor) fan motor (IFM). The blower motor starts instantly.

The cooling cycle remains ``on'' until the room tempera- ture drops to point that is slightly below the cooling control setting of the room thermostat. At this point, the thermostat ``breaks'' the circuit between thermostat termi- nal R to terminals Y and G. These open circuits deenergize contactor coil C and relay coil BR. The condenser and com- pressor motors stop. After a 30-second delay, the blower motor stops. The unit is in a ``standby'' condition, waiting for the next ``call for cooling'' from the room thermostat.

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