Carrier 50EY Service, Ð Cooling Capacity Staging Table, CV Units with 2 Compressors, Ð Door Latch

CAPACITY CONTROL, COOLING Ð The cooling capac- ity staging tables are shown in Tables 18 and 19.

Table 18 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 on Compressor 1 only.

Table 19 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 1 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.

The ®eld test is then complete.

TIME GUARD CIRCUIT Ð The Time Guard function (built into the rooftop's control module board) maintains a mini- mum off time of 5 minutes and a minimum on time of 10 seconds.

CRANKCASE HEATER Ð The 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 outdoor-fan motor(s) at 55 F (one outdoor-fan motor on 024-034 units and 2 outdoor- fan motors on 038-048 units). The head pressure control per- mits the unit to operate with correct condensing temperatures down to 35 F outdoor-air temperature.

MOTORMASTER III DEVICE Ð The Motormaster III Solid-State Head Pressure Control is a ®eld-installed acces- sory, fan speed control device actuated by a temperature sen- sor. The Motormaster III device is speci®cally designed for use on Carrier equipment and controls the outdoor-fan mo- tor speed in response to the saturated condensing tempera- ture. For outdoor temperatures down to −20 F, the Motor- master III device maintains condensing temperature at 100 F.

SERVICE

Before performing service or maintenance operations on unit, turn off main power switch to unit. Turn off ac- cessory heater power switch if applicable. 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. 37.

To open, loosen the latch bolt using a 7¤16-in. wrench. Pivot the latch so it is not in contact with the door. Open the door. To shut, reverse the above procedure.

NOTE: Disassembly of the top cover may be required under special service circumstances. It is very important that the orientation and position of the top cover be marked on the unit prior to disassembly. This will allow proper replace- ment of the top cover onto the unit and prevent rainwater from leaking into the unit.

IMPORTANT: After servicing is completed, make sure door is closed and relatched properly, and that the latches are tight. Failure to do so can result in water leakage into the evaporator section of the unit.

Fig. 37 Ð Door Latch

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