Sequence of Operation
Fan Coil CARRIER CORPORATION ©2020
Integration Guide All rights reserved
21
equipment’s fan for 1 minute every hour during the unoccupied period. The fan operates at the lowest speed
Fan Speed Control - Electric Heat Override - When electric heat is required and active, the control continuously
monitors the supply air temperature to verify it does not rise above the configured Maximum Heating SAT Limit
[90°F (32.2°C) default]. As the SAT approaches the limit minus 10 °F (5.5 °C), the fan speed increases to
ensure the SAT remains below the limit. This provides the most quiet and efficient operation by running the fan at
the lowest speed possible.
Fan Speed Control - DX Cooling override - When DX (direct expansion) mechanical cooling is required and active,
the control continuously monitors the supply air temperature to maintain the SAT at or above the configured
Minimum Cooling SAT Limit [50°F (10°C) default] plus 5 °F (2.7 °C). When the SAT drops below this value,
the fan speed increases to prevent the SAT from dropping further. The fan operates at the lowest speed to
maximize latent capacity during cooling.
Fan Status (Option) - The optional input can be configured as a fan status input. If configured as Fan Status, the
controller compares the status of the fan to the desired commanded state. When the fan is commanded to run
(ON), the fan status is checked and verified to match the commanded state. If the fan status is not on, then a
supply fan alarm is generated after 1 minute and the equipment’s OAD is disabled. If the equipment has hydronic
heat configured, the heating algorithm maintains the desired fan-off setpoint.
Cooling
The Fan Coil operates one stage of DX cooling or chilled water valve (2-position or modulating) to maintain the
desired cooling setpoint. The PI (Proportional-integral) cooling algorithm controls the cooling. The desired Supply
Air Temperature setpoint [Cooling Control Setpoint] is calculated by the controller. This setpoint is compared to
the actual supply air temperature and determines valve operation for modulating or 2-position control valves or
staging for DX control.
The following conditions must be true in order for the cooling algorithm to run:
• Cooling is set to Enable.
• Space temperature reading is valid.
• For 2-pipe systems, the water temperature is suitable for cooling
• Heat mode is not active and for DX, the 5-minute compressor time-guard timer has expired
• OAT is greater than the Cooling Lockout Temperature if OAT is available.
• Condensate Overflow input is Normal.
• If occupied, the SPT is greater than the Occupied Cooling Setpoint.
• If unoccupied, the SPT is greater than the Unoccupied Cooling Setpoint.
If all the above conditions are met, cooling is energized as required, otherwise it is disabled. If cooling is active
and the SAT approaches the minimum SAT limit, the cooling valve modulates closed. (For DX cooling, if the SAT
drops below the configured minimum SAT value plus 5 °F (2.7 °C), the fan is indexed to a higher speed. If this
is insufficient and if the SAT falls below the minimum limit, the DX cooling stage is disabled.)
The configuration screens contain Min SAT and Cooling Lockout, based on outdoor air temperature (OAT). Both
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