Carrier 542E - Manual (Page 10)

NOTE: Adjustment of the refrigerant charge is not required
unless the unit is suspected of not having the proper charge.
An operating pressure/temperature tag is fastened inside
the compressor compartment. (Also see Tables IV and V.)
Use this tag to approximate the charge if ARI rating condi­
tions can not be obtained, when evaluating the refrigerant
charge by checking operating pressures and temperatures.
This method of evaluating ensures that an optimum
refrigerant charge is in the system when the system condi­
tions and components are normal; however, adjusting the
refrigerant charge does not solve or fix system abnor­
malities.
The amount of refrigerant charge affects how efficiently and
economically the unit operates. An overcharged or under­
charged unit leads to diminished efficiency, high operating
costs, and the possibility of premature compressor failure.
CÀUTION; When evaluating the refrigerant charge, an
indicated adjustment to the specified factory charge must
always be very minimal. If a substantial adjustment is indi­
cated, an abnormal condition exists somewhere in the
system; such as insufficient airflow across either coil or both
coils.
When checking the refrigerant using the temperature/pres-
sure evaluation method, adhere to the following criteria:
1. Check refrigerant charge in cooling mode when outdoor
temperature is above 65°F.
2. Check refrigerant charge in heating mode when outdoor
temperature is below 65°F.
3. For best results, do not operate unit continuously for
more than 10 minutes if for any reason charge must be
checked in opposite mode above or below 65°F.
Proceed as follows to evaluate the system performance and
refrigerant charge:
1. Remove caps from low- and high-pressure service fit­
tings. See Figure 8.
2. Attach low- and high-side pressure gauge hoses to low-
and high-pressure service fittings, respectively. Hoses
must have valve core depressors. Gauges must be cali­
brated for accuracy.
3. Set room thermostat below room temperature to start
cooling operation or above room temperature to start
heating operation, depending on outdoor temperature.
Allow unit to operate until conditions stabilize and
pressures level out.
4. Determine and record these conditions:
a. Low- and high-side pressures.
b. Dry-bulb temperature of inlet air at outdoor coil.
c. Temperature of inlet air at return-air grille—creí
bulb if operating in cooling mode or dry bulb if operat­
ing in heating mode.
5. Evaluate system performance and refrigerant charge by
comparing recorded reading with operating pres­
sure/temperature tag.
6. Make slight adjustment to refrigerate charge when
necessary.
NOTE: If the problem causing the inaccurate readings is a
refrigerant leak, see Section V, part B, of these instructions.
C. Indoor Airflow & Airflow Adjustments
CAUTION; The recommended indoor airflow is 350 to 450
ft®/min per each 12,000 Btuh of rated unit capacity. Inade­
quate airflow can cause unsatisfactory operation and per­
formance.
Model 542E, sizes 024 thru 048, and single-phase 060-size
units have direct-drive blower motors. All motors have a
high- and low-speed connection (except for 460-V motors
which have only a high-speed connection).
The system airflow for all direct-drive units (except 460-V)
can be changed, when necessary, by changing the blower
motor speed connection from the factory setting to the
unused speed connection. The factory setting is indicated on
the unit wiring label. For operation of units designed for
208-V and 230-V operation, a blower motor speed connection
may need to be changed. See unit wiring label. See Section
IV, part B, for the procedure.
Model 542D060 and 542E060 3-phase units have belt-drive
blower motors. The system airflow for these units can be
changed, when necessary, by adjusting the blower-motor
pulley as follows:
CAUTION: Increasing the hlower speed places a heavier
load on the motor and increases the current. Do not exceed
the rated full load amperage indicated on the rating plate of
the blower motor.
1. Turn off power at disconnect switch.
2. Relieve belt tension, then remove drive belt from motor
pulley.
3. Loosen setscrew in movable flange on motor pulley and
turn flange either in to increase airflow or out to decrease
airflow.
4. Make sure that setscrew is over flat surface on pulley
hub and tighten setscrew.
5. Replace belt and adjust belt tension for approximately
one inch of sag under normal finger pressure midway
between pulleys.
Tables VI and VII show the air delivery performance at
various external static pressues. Determine the airflow for
the system being installed as follows;
1. Start the unit and measure static pressure in duct
system at unit.
2. Refer to Table VI or VII and determine airflow at static
pressure measured.
NOTE: Be sure that all supply- and return-air grilles are
open, free from obstructions, and adjusted properly.
When using an accessory electric heater, the system airflow
can also be determined by measuring the temperature rise
through the unit, then using the following formula:
AIRFLOW (ftVmin) =
KW
TR
xY
where,
KW = Heater nominal KW at 240 or 480V
TR = Measured temperature rise
Y =
200V 208V 220V 230V 240V
440V 460V 480V
2195 2374 2655 2902 3160
NOTE: Value Y varies with the operating voltage at the heater.
Interpolate to determine the value of Y for voltages not
shown.
CAUTION: When using an accessory electric heater, the
system airflow must be sufficient to prevent the heater limit
switches from tripping off. W'hen using the 20-KW single­
phase heater, the system airflow must be at least 1000
ft^/min.
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