Carrier Air Conditioner specifications Alarms Mode and Sub-Mode Directory

Table 24 — Alarms Mode and Sub-Mode Directory

SUB-MODE	KEYPAD ENTRY		ITEM	ITEM EXPANSION	COMMENT
CRNT			AXXX or TXXX	CURRENTLY ACTIVE ALARMS	Alarms are shown as AXXX.
		ENTER
					Alerts are shown as TXXX.
RCRN			YES/NO	RESET ALL CURRENT ALARMS
		ENTER
HIST			AXXX or TXXX	ALARM HISTORY	Alarms are shown as AXXX.
		ENTER
					Alerts are shown as TXXX.
RHIS			YES/NO	RESET ALARM HISTORY
		ENTER

Table 25 — Example of Reading and Clearing Alarms

SUB-MODE	KEYPAD	ITEM	ITEM EXPANSION	COMMENT
	ENTRY
CRNT	ENTER	AXXX or TXXX	CURRENTLY ACTIVE ALARMS	ACTIVE ALARMS (AXXX) OR
				ALERTS (TXXX) DISPLAYED.
CRNT	ESCAPE
RCRN		NO		Use to clear active alarms/alerts
	ENTER	NO		NO Flashes
		YES		Select YES
	ENTER	NO		Alarms/alerts clear, YES changes to NO

Temperature Reset — The control system is capable of handling leaving-fluid temperature reset based on return cooler fluid temperature. Because the change in temperature through the cooler is a measure of the building load, the return tempera- ture reset is in effect an average building load reset method. The control system is also capable of temperature reset based on outdoor-air temperature (OAT), space temperature (SPT), or from an externally powered 4 to 20 mA signal. Accessory sen- sors must be used for OAT and SPT reset (HH79NZ073 for OAT and HH51BX006 for SPT). The Energy Management Module (EMM) must be used for temperature reset using a 4 to 20 mA signal.

To use the return reset, four variables must be configured. In the Configuration mode under the sub-mode RSET, items CRST, CRT1, CRT2, and DGRC must be set properly. See Ta- ble 26 on page 44 for correct configuration. See Fig. 2-4 for wiring details.

Under normal operation, the chiller will maintain a constant leaving fluid temperature approximately equal to the chilled fluid set point. As the cooler load varies, the entering cooler fluid will change in proportion to the load as shown in Fig. 21. Usually the chiller size and leaving-fluid temperature set point are selected based on a full-load condition. At part load, the flu- id temperature set point may be colder than required. If the leaving fluid temperature was allowed to increase at part load, the efficiency of the machine would increase.

Return temperature reset allows for the leaving temperature set point to be reset upward as a function of the return fluid temperature or, in effect, the building load.

LEGEND

EWT — Entering Water (Fluid) Temperature

LWT — Leaving Water (Fluid) Temperature

Fig. 21 — Standard Chilled Fluid

Temperature Control — No Reset

43