Carrier 50GL-A Instruction Manual download pdf (Page 12)

method for evaluating the unit charge. Do not use mercury or small

dial--type thermometers because they are not adequate for this type

of measurement.

NOTE: Allow system to operate for a minimum of 15 minutes

before checking or adjusting refrigerant charge.

IMPORTANT: When evaluating the refrigerant charge, an

indicated adjustment to the specified factory charge must always be

very minimal. If a substantial adjustment is indicated, an abnormal

condition exists somewhere in the cooling system, such as

insufficient airflow across either coil or both coils.

Proceed as follows:

1. Remove cap from low pressure service fitting.

2. Using hoses with valve core depressors, attach low pressure

gauge hose to low pressure service fittings.

3. Start the unit in cooling mode and let run until system

pressures stabilize.

4. Measure and record the following:

a. Outdoor ambient --air temperature °C db.

b. Evaporator inlet--air temperature °Cwb.

c. Suction--tube temperature °C at low--side service

fitting.

d. Suction (low--side) pressure (kPA).

5. Using “Cooling Charging Tables” compare outdoor--air

temperature °C db with the entering evaporator air temper-

ature °C wb to determine desired superheat temperature.

(See Fig. 13).

6. Using the superheat value in step 5, locate the intersection

of the required superheat with the suction pressure previ-

ously measured. Note the required suction tube temperature.

Using a tolerance of +/-- 1.7°C, add refrigerant if actual

temperature is higher than charted suction tube temperature,

or remove refrigerant if actual temperature is lower than

charted suction tube temperature.

NOTE: If the problem causing the inaccurate readings is a

refrigerant leak, refer to Check for Refrigerant Leaks section.

INDOOR AIRFLOW AND AIRFLOW ADJUST-

MENTS

UNIT OPERATION HAZARD

Failure to follow this caution may result in unit damage.

For cooling operation, the recommended airflow is 350 to

450 cfm for each 12,000 Btuh of rated cooling capacity

(165 to 212 L/s for each 3.5 kW of rated cooling capacity).

CAUTION

NOTE: Be sure that all supply --and return-- air grilles are open,

free from obstructions, and adjusted properly.

ELECTRICAL SHOCK HAZARD

Failure to follow this warning could result in personal

injury or death.

Disconnect electrical power to the unit and install lockout

tag before changing blower speed.

WARNING

This unit is factory-set up for use with a single cooling fan speed.

Airflow can be changed by changing the lead connections of the

blower motor. Insulate r emoved lead end to avoid contact with

chassis parts.

All 50GL units are factory wired for low speed and may need to be

wired for medium or high speed in the field.

A00010

LED STATUS

OFF NoCallforcompressoroperation

FLASHING Reversed phase

ON Normal

Fig. 11 -- Phase Monitor Control and LED Indicators

FOR 4 0 0--V MOTORS

See Table 3 for motor speed colors.

COOLING SEQUENCE OF OPERATION

With the room thermostat SYSTEM switch in the COOL position

and the FAN switch in the AUTO position, the cooling sequence of

operation is as follows:

When the room temperature rises to a point that is slightly above

the cooling control setting of the thermostat, the thermostat

completes the circuit between thermostat terminal R to terminals Y

and G. These completed circuits through the thermostat connect

contactor coil, and indoor fan relay.

The normally open contacts of energized contactor (C) close and

complete the circuit through compressor motor (COMP) to

condenser (outdoor) fan motor (OFM). Both motors start instantly.

A set of normally open contacts on the indoor fan relay (R) are

closed which energizes a circuit to the indoor fan motor.

NOTE: Once the compressor has started and then has stopped, it

should not be started again until 5 minutes have elapsed.

The cooling cycle remains on until the room temperature drops to a

point that is slightly below the cooling control setting of the room

thermostat. At this point, the thermostat breaks the circuit between

thermostat terminal R to terminals Y and G. These open circuits

deenergize contactor coil C and R. The condenser and compressor

motors stop. The unit is in a standby condition, waiting for the next

call for cooling from the room thermostat.

50GL-- A

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Carrier 50GL-A Instruction Manual Page 12

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