Carrier 17EX specifications MAINT01, MAINT02, MAINT03, MAINT04, Occdefm, Wsmdefme

4.A high pressure point can also be calibrated between 240 and 260 psig (1655 and 1793 kPa) by attaching a regu- lated 250 psig (1724 kPa) pressure (usually from a ni- trogen cylinder). The high pressure point can be calibrated by accessing the appropriate transducer on the

STATUS01 screen, highlighting the transducer, pressing

the SELECT softkey, and then increasing or decreasing the value to the exact pressure on the refrigerant gage.

Press ENTER to ®nish. High altitude locations must com- pensate the pressure so that the temperature/pressure re- lationship is correct.

If the transducer reading returns to the previous value and the pressure is within the allowed range, check the volt- age ratio of the transducer. Refer to Step 3 above. The voltage ratio for this high pressure calibration must be between 0.585 and 0.634 vdc to allow calibration. Change the pressure at the transducer until the ratio is within the acceptable range. Then attempt to calibrate to the new pressure input.

The PIC will not allow calibration if the transducer is too far out of calibration. A new transducer must be installed and re-calibrated.

OIL DIFFERENTIAL PRESSURE/POWER SUPPLY MOD- ULE CALIBRATION Ð (See Fig. 48.) The oil reservoir in the 17EX chiller is not common to cooler pressure. There- fore, a comparison of pump output to cooler pressure can not be used to provide differential oil pressure information. A different method has been developed.

Oil transmission sump pressure and oil supply pressure are fed to a comparator circuit on a 5V power supply board. The output of this circuit, which represents differential oil pressure, is fed to the PSIO. The oil differential pressure is calibrated to 0 psid (0 kPad) by selecting the oil pressure input on the STATUS01 screen. Then, with the oil pump turned

OFF and the transducers connected, press the ENTER soft-

key to zero the point. No high end calibration is needed or possible.

17EX OIL PRESSURE INPUT

Fig. 48 Ð Oil Differential Pressure/Power

Supply Module

TROUBLESHOOTING TRANSDUCERS Ð When trouble- shooting transducers, keep the negative lead of your volt- ohmmeter on terminal U4 of the power supply (or terminal 4 on power supplies without the comparator circuit).

Voltage VO1 = (VH1-VL1) + .467 ± .1 V

For all PIC transducers:

Measured pressure = (507.97 × (V out/Vin) ) − 47.33

Vout = transducer output ref. to neg. terminal (4 or U4) i.e., VH1 to U4 or VL1 to U4

Vin = power supply output, i.e., U3 to U4

TRANSDUCER REPLACEMENT Ð Since the transduc- ers are mounted on Schrader-type ®ttings, there is no need to remove refrigerant from the vessel. Disconnect the trans- ducer wiring by pulling up on the locking tab while pulling up on the weather-tight connecting plug from the end of the transducer. Do not pull on the transducer wires. Unscrew the transducer from the Schrader ®tting. When installing a new transducer, do not use pipe sealer, which can plug the sensor. Put the plug connector back on the sensor and snap into place. Check for refrigerant leaks.

Make sure to use a backup wrench on the Schrader ®t- ting whenever removing a transducer.

Control Algorithms Checkout Procedure Ð One of the tables in the SERVICE menu is the CONTROL AL- GORITHM STATUS table. This table has 6 screens that may be viewed to see how a particular control algorithm is operating, that is, to see what parameters and values the PIC is using to control the chiller.

MAINT01	Capacity	The values used to calculate the chilled
	Control	water/brine control point.
MAINT02	Override	Details of all chilled water control over-
	Status	ride values
MAINT03	Surge/	The surge and hot gas bypass control
	HGBP	algorithm status as well as the values
	Status	dealing with this control.
MAINT04	LEAD/LAG	LEAD/LAG operation status.
	Status
OCCDEFM	Time	The Local and CCN occupied sched-
	Schedules	ules, displayed in a way that allows the
	Status	operator to quickly determine whether
		the schedule is in an occupied period
		or not.
WSMDEFME	Water	The status of the WSM (water system
	System	manager), a CCN module that can turn
	Manager	on the chiller and change the chilled
	Status	water control point.

These maintenance tables are very useful in determining guide vane position, reaction from load changes, control point overrides, hot gas bypass reaction, surge prevention, etc.

Control Test Ð The control test feature can check all the thermistor temperature sensors, including those on the Options modules, pressure transducers, pumps and their as- sociated ¯ow switches, the guide vane actuator, and other control outputs, such as hot gas bypass. The tests can help to determine whether a switch is defective, or a pump relay is not operating, among other useful troubleshooting tests.

During pumpdown operations, the pumps are energized to prevent freeze-up, and the vessel pressures and tempera- tures are displayed. The pumpdown/lockout feature pre- vents the compressor from starting up when there is no re- frigerant in the chiller or when the vessels are isolated. The operator then uses the terminate lockout screen to end the pumpdown lockout after the pumpdown procedure is re- versed and refrigerant is added.

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