If this condition is encountered, see Possible Causes for Alarms 56 and 57 on page 75.
HIGH DGT CIRCUIT A
HIGH DGT CIRCUIT B — The capacity of the affected circuit may be increased to reduce circuit discharge gas temperature.
HIGH PRES OVERRIDE CIR A
HIGH PRES OVERRIDE CIR B — This mode is checked for when the circuit is ON. The appropriate circuit mode will be active if the discharge pressure for the circuit, Discharge Pressure Circuit A (Discharge Pressure, DP.A), Discharge Pressure Circuit B (Discharge Pressure, DP.B), or Discharge Pressure Circuit C (Discharge Pressure, DP.C), is greater than the High Pressure Threshold (High Pressure Threshold, HP.TH).
The capacity of the affected circuit will be reduced. Two minutes following the capacity reduction, the circuit’s saturated condensing temperature (SCTt+2) is calculated and stored. The affected circuit will not be allowed to add capacity for at least 5 minutes following the capacity reduction. If after 5 minutes, the circuit’s saturated condensing temperature is less than SCTt+2 –3° F (1.7° C), and then if required, percent capacity will be added. If additional capacity is required, the control will look for other circuits to add capacity.
This mode will terminate once the circuit’s saturated con- densing temperature is less than SCTt+2 –3° F (1.7° C).
If this condition is encountered, see Possible Causes for Alarm A1.03. on page 81.
LOW SUPERHEAT CIRCUIT A
LOW SUPERHEAT CIRCUIT B — This mode is checked for when the circuit is ON. The appropriate circuit mode will be active if the circuit’s superheat (discharge gas temperature
— SCT) is less than 18° F (10° C).
No additional capacity will be added until the circuit’s su- perheat is greater than 18° F (10° C). The control will look for other circuits to add capacity if additional steps of capacity are required. This mode will terminate once the affected circuit’s superheat is greater than 18° F (10° C).
If this condition is encountered, see Possible Causes for Alarms P.11 and P.12 on page 77.
Sensors — The electronic control uses up to 13 thermistors to sense temperatures and up to 8 transducers to sense pressure for controlling chiller operation. These sensors are outlined below. See Fig. 38 for thermistor and transducer locations.
THERMISTORS (Tables 38-39B) — Thermistors that are monitoring the chiller’s operation include: Cooler Entering Water, Cooler Leaving Water, Condenser Entering Water, Condenser Leaving Water, Dual Chiller Leaving Water, Com- pressor Suction Gas Temperature, Compressor Discharge Gas Temperature, Economizer Temperature, and Compressor Motor Temperature. These thermistors are 5 kΩ at 77 F (25 C) and are identical in temperature versus resistance. The Space Tempera- ture Thermistor is 10 kΩ at 77 F (25 C) and has a different tem- perature vs. resistance. See Fig. 38 for thermistor locations.
Cooler Leaving Water Sensor — On all sizes, this thermistor is installed in a well in the leaving water nozzle of the cooler. See Fig. 39 and 40.
Cooler Entering Water Sensor — On all sizes, this thermis- tor is factory-installed in a well in the entering water nozzle of the cooler.
Condenser Leaving Water Sensor — On all sizes with heat machine options, this thermistor is installed in a well in the leaving water nozzle of the condenser. See Fig. 39 and 40.
Condenser Entering Water Sensor — On all sizes with heat machine options, this thermistor is factory-installed in a well in the entering water nozzle of the condenser.
Compressor Suction Gas Temperature — On all sizes, this thermistor is factory-installed in a well located on the compres- sor of each circuit. There is one thermistor for each circuit.
Compressor Discharge Gas Temperature — On all sizes, this thermistor is factory-installed in a well located in the discharge end of the compressor for the circuit. There is one thermistor for each circuit.
Economizer Temperature (sizes 175,200,350,400 only) — On all sizes, this thermistor is factory-installed in a friction fit well located in the economizer line for the circuit. There is one thermistor for each circuit.
Compressor Motor Temperature — On all sizes, this therm- istor is embedded in the motor windings. There are two therm- istors in each compressor. One spare is provided.
Remote Space Temperature — This sensor (part no. 33ZCT55SPT) is a field-installed accessory mounted in the in- door space and is used for water temperature reset. The sensor should be installed as a wall-mounted thermostat would be (in the conditioned space where it will not be subjected to either a cooling or heating source or direct exposure to sunlight, and 4 to 5 ft above the floor).
Space temperature sensor wires are to be connected to terminals in the unit main control box. The space temperature sensor includes a terminal block (SEN) and a RJ11 female con- nector. The RJ11 connector is used to access the Carrier Com- fort Network® (CCN) system at the sensor. See Fig. 39 and 40. To connect the space temperature sensor (see Fig. 41):
1.Using a 20 AWG twisted pair conductor cable rated for the application, connect one wire of the twisted pair to one SEN terminal and connect the other wire to the other SEN terminal located under the cover of the space temperature sensor.
2.Connect the other ends of the wires to terminals 7 and 8 on TB6 located in the unit control box.
Units on the CCN can be monitored from the space at the sensor through the RJ11 connector, if desired. To wire the RJ11 connector into the CCN:
1.Cut the CCN wire and strip ends of the red (+), white (ground), and black (–) conductors. (If another wire color scheme is used, strip ends of appropriate wires.)
2.Insert and secure the red (+) wire to terminal 5 of the space temperature sensor terminal block.
3.Insert and secure the white (ground) wire to terminal 4 of the space temperature sensor.
4.Insert and secure the black (–) wire to terminal 2 of the space temperature sensor.
IMPORTANT: The cable selected for the RJ11 connector wiring MUST be identical to the CCN communication bus wire used for the entire network. Refer to Table 11 for acceptable wiring.
5.Connect the other end of the communication bus cable to the remainder of the CCN communication bus.
NOTE: The Energy Management Module (EMM) is required for this accessory.
TRANSDUCERS — There are four pressure transducers per circuit (3 per circuit for sizes 150,325), and two different types of transducers: low pressure (green connector) and high pres- sure (black connector). See Fig. 38 for transducer locations.
Low-pressure type:
•Suction pressure transducer (SPT)
•Economizer pressure transducer (EPT)
High-pressure type:
•Discharge pressure transducer (DPT)
•Oil pressure transducer (OPT)
