Carrier 48EJ, EW, EK, EY024-048 Cooling Capacity Staging Table, CV Units With 2 Compressors, Stages

·When the outdoor air quality is greater than the outdoor air quality set point (ppm)

High priority Ð When the priority is set to high, the IAQ set point controls the outside air damper exclusively, with no regard to comfort conditioning.

TIME GUARD CIRCUIT Ð The Time Guard function (built into the rooftop control board) maintains a minimum off time of 5 minutes, a minimum on time of 10 seconds, and a 10-second delay between compressor starts.

CRANKCASE HEATER Ð Unit main power supply must remain on to provide crankcase heater operation. The crank- case heater in each compressor keeps oil free of refrigerant while compressor is off.

HEAD PRESSURE CONTROL Ð Each unit has a fan cy- cling, outdoor thermostat to shut off the outdoor-fan mo- tor(s) at 55 F (one outdoor-fan motor on 024-034 units and two outdoor fan motors on 038-048 units). The head pres- sure control permits unit to operate with correct condensing temperatures down to 35 F outdoor-air temperature.

MOTORMASTER III CONTROL Ð The Motormaster

IIISolid-State Head Pressure Control is a ®eld-installed ac- cessory fan speed control device actuated by a temperature sensor. It is speci®cally designed for use on Carrier equip- ment and controls the condenser-fan motor speed in re- sponse to the saturated condensing temperature. For outdoor temperatures down to −20 F, it maintains condensing tem- perature at 100 F. Refer to the accessory Motormaster in- stallation instructions for more information.

CAPACITY CONTROL, COOLING Ð The cooling capac- ity staging tables are shown in Tables 20 and 21.

Table 20 Ð 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 pres- sure unloaders to Compressor 1 only.

Table 21 Ð 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.

FIELD TEST Ð The ®eld test program is initiated by mov- ing up DIP switch no. 4 to the OPEN position. The outdoor- air damper will close. The control allows 90 seconds for the damper to close in case it was in the full open position. Next, the indoor-fan contactor will be energized, and the outside- air damper will begin to open to its default value of 20% and stay at that position for a short period of time. The outdoor- air damper will then open to its full open position and stay at that position for a short period of time. The outdoor-air damper will then close.

If the unit is equipped with power exhaust, stage 1 will be energized for 5 seconds. If the unit is con®gured for stage 2 of power exhaust, stage 2 will be energized for 5 seconds after the ®rst stage is deenergized.

The ®rst stage of heat will be energized for 30 seconds, after which the second stage heat will be energized for an additional 30 seconds. Heat is then deenergized.

The last step is the Cooling mode. Outdoor-fan contactor no. 1 is energized. This is followed by each stage of cooling energized with a 10-second delay between stages. After this is complete, outdoor-fan contactor no. 2 is energized for 10 seconds.

The compressors will now deenergize, followed by the outdoor-fan contactors and indoor-fan contactors. If the unit is equipped with the Integrated Gas Control (IGC) board, the indoor fan will continue to operate for an additional 30 seconds after deenergizing the circuit.

The ®eld test is then complete.

SERVICE

Before performing service or maintenance operations on unit, turn off main power switch to unit. Electrical shock could cause personal injury.

Service Access Ð All unit components can be reached through clearly labelled hinged access doors. These doors are not equipped with tiebacks, so if heavy duty servicing is needed, either remove them or prop them open to prevent accidental closure.

Each door is held closed with 3 latches. The latches are secured to the unit with a single 1¤4-in. - 20 x 1¤2-in. long bolt. See Fig. 45.

Fig. 45 Ð Door Latch

44