Carrier 50SS018-060, 50SX024-060 owner manual Sequence of Operation Ð STD NON-ICM Units

SEQUENCE OF OPERATION Ð STD NON-ICM UNITS

Cooling

NOTE: With the FAN switch in the ON position, 24 v is supplied to the IFR through the G terminal on the thermo- stat. This voltage energizes the coil of the contactor, closing the normally-open set of contacts which provide continuous power to the indoor (evaporator) fan motor (IFM). Moving the FAN switch back to the AUTO. position, providing there is not a call for cooling, deenergizes the IFR, opens the IFR contacts, and deenergizes the IFM. The FAN switch in AUTO. position cycles upon a call for cooling.

On a call for cooling, 24 v is supplied to the compressor contactor (C) and IFR simultaneously through the Y and G terminals of the thermostat, respectively. On units with a compressor time delay relay, there is a built-in, 5-minute (± 45 seconds) delay between compressor starts. Energizing the contactor closes the normally-open set of contacts sup- plying power to both the compressor and outdoor (con- denser) fan motor (OFM). Energizing the IFR closes the normally-open set of contacts providing power to the IFM. On the loss of the call for cooling, 24 v is removed from both the Y and G terminals of the thermostat (providing the FAN switch is in the AUTO. position), deenergizing both the contactor and IFR and opening both the contacts sup- plying power to compressor/OFM and IFM.

Heating Ð If accessory electric heaters are installed, on a call for heat, circuit R-W is made through the thermostat con- tacts. Circuit R-G is made which energizes the IFR. If the heaters are staged, then the thermostat closes a second set of contacts W2 when second stage is required. When thermo- stat is satis®ed, contacts open, deenergizing the heater relay and the IFR.

SEQUENCE OF OPERATION Ð ICM UNITS

Evaporator Fan Ð With the fan switch in the ON position, 24 v is supplied to the ICM motor through the ``G'' terminal on the thermostat. This voltage provides continuous power to the indoor (evaporator) fan motor (IFM). If the fan switch is moved back to the AUTO position and there is not a call for heating or cooling, 24 v is removed from the ``G'' ter- minal and the evaporator fan remains energized for the de- lay timing. When the fan switch is in AUTO, the fan cycles with either the call for heating or cooling.

Cooling Ð On a call for cooling, 24 v is supplied to the com- pressor contactor (C) and IFM simultaneously through the ``Y'' and ``G'' terminals of the thermostat. Energizing the contactor closes the normally open set of contacts supplying power to both the compressor and outdoor (condenser) fan motor (OFM). On the loss of the call for cooling, 24 v is removed from the ``Y'' and ``G'' terminals of the thermostat, deenergizing the compressor and OFM. The evaporator fan remains energized for the delay timing.

NOTE: Once the compressor has started and then stopped, it cannot be restarted again until 5 minutes have elapsed.

Heating Ð If accessory electric heaters are installed, on a call for heat, circuits R-W and R-G are made through the thermostat contacts, energizing the heater relay and IFM. If the heaters are staged, then the thermostat closes the second set of contacts, W2, when the second stage is required. When the thermostat is satis®ed, contacts open, deenergizing the heater relay and the IFM.

35