Carrier PrimeLINE 69NT40-561-200, Operation And Service Manual

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T-362 4–28
4.3.23 Protection Modes of Operation
Evaporator Fan Operation
Opening of an evaporator fan internal protector will shut down the unit.
Failure Action
Function code Cd29 may be operator set to select the action the controller will take upon a system failure. The
factory default is full system shutdown. See Table 4–4 .
Generator Protection
Function codes Cd31 (Stagger Start, Offset Time) and Cd32 (Current Limit) may be operator set to control the start
up sequence of multiple units and operating current draw. The factory default allows on demand starting (no delay)
of units and normal current draw. See Table 4–4 .
Compressor High Temperature Protection
The controller continuously monitors compressor discharge pressure and temperature, and suction pressure. If
discharge pressure or temperature rises above the allowed limit or suction pressure falls below the allowed limit,
the compressor will be cycled off and on every 3 minutes. Condenser and evaporator fans will continue to operate
during the compressor off cycle.
If high compressor dome temperature occurs, as measured by the CPDS, the controller will allow additional
refrigerant to be released into the system in order to provide cooling to the evaporator coil and compressor dome.
The controller is alerted to high compressor dome temperatures via the CPDS when ambient temperature is
greater than 43.3°C (110°F), return air temperature is less than -17.5°C (0.5°F) and the compressor discharge
temperature is greater than 117.7°C (244°F).
Dome temperature control logic will disengage when return air temperature and ambient temperature return to
allowed limits or when the compressor turns off.
Compressor Low Pressure Protection
If the suction pressure low limit is triggered, the DUV will energize to raise the suction pressure.
Perishable Mode - System Pressure Regulation
In Perishable mode, system pressures may need to be regulated at ambient temperatures of 20°C (68°F) and
below. Once below this ambient temperature, the condenser fan may cycle on and off based on limits imposed for
discharge pressure. For extremely cold ambient temperatures, -18°C (0°F), heater cycling may occur within normal
system operation based on discharge pressure limits.
Condenser Fan Override
When CnF17 (Discharge Temperature Sensor) is set to “In” and CnF48 (Condenser Fan Switch Override) is set to
“On”, the condenser fan switch override logic is activated. If condenser cooling water pressure is sufficient to open
the water pressure switch (de-energizing the condenser fan) when water flow or pressure conditions are not
maintaining discharge temperature, the logic will energize the condenser fan as follows:
1. If the DUV is less than 80% open when the controller calls for it to be100% open, the condenser fan is
energized. When the DUV is 100% open, the fan will de-energize.
2. If DPT reading is invalid or out of range (AL65), the condenser fan is energized and will remain energized
until system power is cycled.
3. If the system is running on condenser fan override and the high pressure switch opens, the condenser fan is
energized and will remain energized until the system power is cycled.
4.3.24 QUEST Mode
QUEST is a method of temperature control using compressor-cycle during steady-state perishable cooling (also
referred to as Compressor-Cycle Perishable Cooling, CCPC) that cycles the compressor on and off according to
return air temperature.
To be eligible for steady-state control, the unit must first complete a setpoint pulldown phase and a QUEST pulldown
phase:
• During setpoint pulldown, supply air temperature is controlled according to the unit’s nominal supply air setpoint.