Carrier 50XT manual Controls, Sequence of Operation

CONTROLS

Sequence of Operation

The 50XT packaged heat pump is designed for installation with a communicating UI. This unit will not respond to commands provided by a common thermostat except under certain emergency situations.

The UI uses temperature, humidity and other data supplied from indoor and outdoor system components to control heating or cooling system for optimum comfort. The unit will be commanded by the UI to supply airflow. The unit will operate the indoor fan at requested airflow for most modes.

The nominal requested airflow in high stage will be 350 cfm per ton of nominal cooling capacity as defined by unit size. Actual airflow request will be adjusted from nominal using indoor and outdoor temperature and indoor humidity data to optimize the system operation for occupant comfort and system efficiency. Refer to UI literature for further system control details.

Airflow during electric heater operation must be greater than a minimum level for safe operation. If UI instructs unit to turn on electric heat and the requested airflow is less than the minimum level the fan coil control will override requested value.

NOTE: Once the compressor has started and then has stopped, it should not be started again until 4 minutes have elapsed. The cooling cycle remains “on” until the room temperature drops to point that is slightly below the cooling control setting of the UI.

COOLING AND HEATING OPERATION

With a call for first stage cooling, the outdoor fan, reversing valve, and low stage compressor are energized. If low-stage cannot satisfy cooling demand, high-stage cooling is energized by the UI. After second stage is satisfied, the unit returns to low-stage operation until first stage is satisfied or until second stage is required again. When both first stage and second stage cooling are

satisfied, the compressor will shut off. The reversing valve will remain energized until the control board power is removed or a call for heating is initiated. With a call for heating, the outdoor fan and compressor are energized. The compressor will operate in high or low stage operation, as needed, to meet the heating demand. When the heating demand is satisfied, the compressor and fan will shut off. The reversing valve is de-energized in the heating mode.

NOTE: When two-stage unit is operating at low-stage, system vapor (suction) pressure will be higher than a standard single-stage system or high-stage operation.

NOTE: Outdoor fan motor will continue to operate for one minute after compressor shuts off, when outdoor ambient is greater than or equal to 100°F (38°C).

UTILITY INTERFACE WITH INFINITY CONTROL

The utility curtailment relay should be connected to factory supplied pigtails (PINK connected to R, VIOLET connected to Y2 on the control board) located in the low voltage splice box (see Typical Wiring Schematic ). This input allows a power utility device to interrupt compressor operation during peak load periods. When the utility sends a signal to shut the system down, the UI will display “Curtailment Active”.

Infinity Controlled Low Ambient Cooling

NOTE: When this unit is operating below 55_F (12.7°C) outdoor temperature, provisions must be made for low ambient operation. This unit is capable of low ambient cooling down to 0_F (-17.7°C)ONLY when using the Infinity control. A low ambient kit is not required, and the outdoor fan motor does not need to be replaced for Infinity controlled low ambient operation. Low ambient cooling must be enabled in the UI set-up.Fan may not begin to cycle until about 40_F (4.4°C) OAT. Fan will cycle based on coil and outdoor air temperature.

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