Carrier 30XW325-400 manual Controls cont, Safeties

Controls (cont)

•Evaporator entering fluid temperature (T2)

•Suction gas temperature (T4 - Circuit A, T7 - Circuit B)

•Economizer gas temperature (T5 - Circuit A, T11 - Circuit B) (sizes 350, 400 only)

•Space temperature (T8)

•Discharge gas temperature (T9 - Circuit A, T10 - Circuit B)

•Condenser entering fluid temperature (T12)

•Condenser leaving fluid temperature (T13)

•Compressor motor temperature

There are 3 (size 325) or 4 (sizes 350, 400) refrigerant pressure transducers used in each circuit for sensing suc- tion, discharge, oil, and economizer (sizes 350, 400) pres- sure. The microprocessor uses these inputs to control capacity.

•Saturated condensing temperature

•Evaporator saturation temperature

Electronic expansion valve (EXV) — The EXV con- trols refrigerant flow to the evaporator for different operat- ing conditions by varying an orifice size to increase or decrease the flow area through the valve based on micro- processor input. The orifice is positioned by a stepper motor through approximately 3,600 discrete steps and is monitored every 3 seconds.

Safeties

Abnormal conditions — All control safeties in the chiller operate through compressor protection board, control relays or the chiller microprocessor. Loss of feedback sig- nal to the MBB will cause the compressor(s) to shut down. For other safeties, the microprocessor makes appropriate decision to shut down a compressor due to a safety trip or bad sensor reading and displays the appropriate failure code on the display. Chiller holds in safety mode until reset; it then reverts to normal control when the unit is reset.

Low-pressure safety — This safety will shut down the chiller and display the appropriate alarm code if the system pressure drops below configured minimums.

High-pressure safety — This safety will shut down the chiller and display the appropriate alarm code if the com- pressor discharge pressure increases to 185 psig for stan- dard condenser units or 250 psig for high condensing or heat machine units.

Compressor anti-cycling — This feature monitors com- pressor starts to limit compressor cycling during periods of low load.

Loss of flow protection — This feature will shut off the chiller if the detected flow is below the configured mini- mum flow rate. Thermal dispersion flow switches are installed in 30XW chillers to confirm evaporator flow.

Sensor failures — The microprocessor monitors tem- perature and pressure sensors to ensure readings are within the expected range. Loss of communication to a sensor or readings outside of the expected range will prompt corrective action.

Other safeties — Other safety features include electric overload, thermal overload protection, oil pressure, loss of refrigerant charge, loss of phase protection, reverse rotation protection (prevents compressor start), current imbalance, and ground current.

Demand limit function — This function can be used to limit the total power draw of the chiller to a user-defined set point. The optional energy management module is required and can provide either 2-step or 4 to 20 mA demand limit. This optional electronic board interfaces with the microprocessor to control the number of com- pressors operating and their operating capacity to limit power consumption to the user specified value.

The microprocessor can control the number of compres- sors operating and their operating capacity to limit power consumption to the user specified value.

Diagnostics — The microprocessor includes a service test feature that displays the condition of each sensor and switch in the chiller and allows the observer to check for proper operation of the compressors. Refer to the Con- trols, Start Up, Operation, Service and Troubleshooting guide for further information.

Default settings — To facilitate quick start-ups, 30XW chillers are pre-configured with a default setting that assumes stand-alone operation with a 44 F (6.6 C) chilled water set point. Configuration settings will be based on any options or accessories included with the unit at the time of manufacturing. Date and time are set to U.S.A. Eastern Time zone and will need reconfiguring based on location and local time zone. If operation based on occupancy schedule is desired, the schedule must be set during installation.

Additional information — Detailed information on con- trols and operation is available in the Controls, Start-Up, Operation, Service and Troubleshooting guide included with each unit. Packaged Service Training programs are also available. Contact your local Carrier representative for more information.

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