Carrier 48EW Smoke Control Modes, Cooling Capacity Staging Table, CV, Units with 2 Compressors

Table 41 — Smoke Control Modes

DEVICE	PRESSURIZATION	SMOKE PURGE	EVACUATION	FIRE SHUTDOWN
Economizer	100%	100%	100%	0%
Indoor Fan/VFD	ON	ON	OFF	OFF
Power Exhaust (all outputs)	OFF	ON	ON	OFF
Heat Stages	OFF	OFF	OFF	OFF
Cool Stages	OFF	OFF	OFF	OFF
HIR	ON	ON	OFF	OFF
LEGEND
HIR — Heat Interlock Relay
VFD — Variable Frequency Drive

HEAD PRESSURE CONTROL — Each unit has a fan cy- cling, outdoor thermostat to shut off the outdoor-fan motor(s) at 55 F (one outdoor-fan motor on 48AJ,AK,AW,AY020-030 and 48EJ,EK,EW,EY024-034 units, 2 outdoor-fan motors on 48AJ,AK,AW,AY035-050 and 48EJ,EK,EW,EY038-048 units and 3 outdoor-fan motors on 48AJ,AK,AW,AY060 and 48EJ,EK,EW,EY054-068 units). The head pressure control permits unit to operate with correct condensing temperatures down to 35 F outdoor-air temperature.

MOTORMASTER® III CONTROL — The Motormaster III Solid-State Head Pressure Control is a field-installed accessory fan speed control device actuated by a temperature sensor. It is specifically designed for use on Carrier equipment and con- trols the condenser-fan motor speed in response to the saturated condensing temperature. For outdoor temperatures down to –20 F, it maintains condensing temperature at 100 F. Refer to the accessory Motormaster installation instructions for more information.

CAPACITY CONTROL, COOLING — The cooling capaci- ty staging tables are shown in Tables 42 and 43.

Table 42 — Cooling Capacity Staging Table, CV

Units with 2 Compressors

		Stages
	0	1	2	3
		Economizer
Compressor 1	off	off	on	on
Compressor 2	off	off	off	on

NOTE: On CV units that require additional unloading, add suction pressure unloaders to Compressor 1 only.

Table 43 — Cooling Capacity Staging Table VAV Units with 2 Compressors and 2 Unloaders*

				STAGES
	0	1	2		3	4	5	6
Compressor 1	off	on	on		on	on	on	on
Unloader 1	off	on	on		off	on	on	off
Unloader 2	off	on	off		off	on	off	off
Compressor 2	off	off	off		off	on	on	on

*40 ton units have only one unloader.

It is often desirable to use a variable air volume (VAV) unit in a variable volume and temperature (VVT) control system because of the greater unloading capability. A VAV unit (with software version 4.0 and later) can easily be configured in the field to run off of either space thermostat (VVT® relay pack) input or a space sensor. When configured in this manner, the unit control will turn on compressors based upon load in the space. If the supply-air falls below predefined limits, the con- trol will unload the compressor in order to maintain the mini- mum supply-air limit. If unloading is not successful in main- taining the minimum supply-air temperature (SAT), then the compressors will be turned off. An alarm will be issued when the compressors are turned off.

A VAV unit configured to run off thermostat input or a space sensor will have the capability for two stages of heating, however, modification to the control wiring will be required to make this available. The Variable Frequency Drive (VFD) for the supply fan will still be active, varying the supply air fan speed to maintain supply duct pressure.

Upon a call for Y1 (or Y2_SPT) cooling, the compressor 1 will start after appropriate Time Guard® functions. Thirty sec- onds after the SAT drops below the “SAT1TRIP” the compres- sor will be unloaded. The unloading sequence will be as follows:

Compressor no. 1	On, Full Load	Unloader no. 1 and no. 2 Off
Compressor no. 1	On, 2/3 Load	Unloader no. 1 Off, Unloader no. 2 On
Compressor no. 1	On, 1/3 Load	Unloader no. 1 and no. 2 On
Compressor no. 1	Off	Unloader no. 1 and no. 2 Off

The “Y1 Low SAT Limit” has an adjustable range from

50 F to 65 F, with a factory setting of 53 F. If the temperature of the SAT rise above the “Y1 Low SAT Limit” plus 2° F, the compressor will be loaded in the reverse order in which it was unloaded following the pre-described time guards. There will be a 90-second time guard between any change in unloaded state, and the normal 5-minute time guard for change in com- pressor On/Off state.

If compressor no. 1 is forced off due to “Y1 LOW SAT Limit” an alert will be issued. If economizer is suitable, the economizer mode will remain active. The alert will be cleared after the 5-minute time guard has expired and the compressor is restarted. With Y1 (or Y1_SPT) input, only compressor no. 1 can be running.

Upon a call for Y1 (or Y1_SPT) and Y2 (or Y2_SPT) cool- ing both compressor no. 1 and 2 will start after appropriate time guards. Thirty seconds after SAT drops below the “Y2 Low SAT Limit” the compressor will be unloaded. The unloading sequence will be as follows:

Compressor no. 1	Unloader no. 1 and no. 2 Off		Compressor no. 2 On
On, Full Load
Compressor no. 1	Unloader no. 1	Off,	Compressor no. 2 On
On, 2/3 Load	Unloader no. 2	On
Compressor no. 1	Unloader no. 1 and no. 2 On		Compressor no. 2 On
On, 1/3 Load
Compressor no. 1	Unloader no. 1 and no. 2 Off		Compressor no. 2 Off
On, Full Load
Compressor no. 1	Unloader no. 1	Off,	Compressor no. 2 Off
On, 2/3 Load	Unloader no. 2	On
Compressor no. 1	Unloader no. 1 and no. 2 On		Compressor no. 2 Off
On, 1/3 Load
Compressor no. 1 Off	Unloader no. 1 and no. 2 Off		Compressor no. 2 Off

The “Y2 Low SAT Limit” has an adjustable range from

45 F to 55 F, with a factory default setting of 48 F. If the tem- perature of the SAT rise above the “Y2 Low SAT Limit” plus 2° F, the compressor will be loaded in the reverse order in which it was unloaded following the pre-described Time Guard functions. There will be a 90-second time guard between any change in unloaded state, and the normal 5-minute time guard for change in compressor On/Off state.

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