Carrier 48NHT024 - Cooling Section Startup and Adjustments

blower motor. Check blower wheel for correct rotation as
indicated by arrow on blower housing. If blower wheel
rotates in opposite direction, reverse any two blower motor
leads or any two line voltage leads. Recheck blower wheel
rotation if necessary to reverse leads.
B. Checking and Adjusting Refrigerant Charge
The refrigerant system is fully charged with R-22 refriger¬
ant, tested, and factory-sealed.
NOTE: Adjustment of the refrigerant charge is not required
unless the unit is suspected of not having the proper R-22
charge. For all applications, the correct R-22 charge for the
best performance is the charge that results in a suction gas
superheat of 5 F at the compressor inlet when the unit is
operating at the ARI rating conditions of 95 F DB outdoor
and 80 F DB/67 F WB indoor.
A superheat charging label is attached to the outside of the
compressor access door. The label includes a “Field Super¬
heat Charging Table” and a “Required Suction-Tube (F)”
temperature chart.
An accurate superheat thermocouple-, or thermistor-type
thermometer, a sling psychrometer, and a gauge manifold
are required when using the superheat charging 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.
A CAUTION
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
cooling system; such as insufficient airflow across
either coil or both coils.
Proceed as follows:
1. Remove caps from low- and high-pressure service
fittings.
2. Using hoses with valve core depressors, attach low-and
high-pressure gauge hoses to low- and high-pressure
service fittings, respectively.
3. Start unit in cooling mode and let unit run until system
pressures stabilize.
4. Measure and record the following:
a. Outdoor ambient-air temperature (F DB).
b. Evaporator inlet-air temperature (F WB).
c. Suction-tube temperature (F) at low-side service fit¬
ting.
d. Suction (low-side) pressure (PSIG).
5. Using “Field Superheat Charging Table," compare
PILOT FLAME BURNER FLAME
outdoor-air temperature (F DB) with evaporator inlet-
air temperature (F WB) to determine desired system
operating superheat temperature. See Table 10.
6. Next, using “Required Suction-Tube (F)” table, com¬
pare desired superheat temperature with suction (low-
side) operating pressure (PSIG) to determine proper
suction-tube temperature. See Table 11.
7. Compare actual suction-tube temperature with proper
suction-tube temperature. Using a tolerance of ,± 3 F,
add refrigerant if actual temperature is more than 3 F
higher than proper suction-tube temperature, or
remove refrigerant if actual temperature is more than
3 F lower than required suction-tube temperature.
NOTE: If the problem causing the inaccurate readings is a
refrigerant leak, see Step 7, part B, of these instructions.
C. Indoor Airflow and Airflow Adjustments
A CAUTION
For cooling operation, the recommended airflow is 350
to 450 Cfm per each 12,000 Btuh of rated cooling capac¬
ity. For heating operation, the airflow must produce a
temperature rise that falls within the range stamped on
the unit rating plate.
Model 018-048 size units have direct-drive blower motors.
Blower motors are factory-connected to deliver the proper
heating and cooling airflows at normal external static pres¬
sures (medium speed cooling, low speed heating for 230v
units and high speed cooling, heating for 460v units).
060 size units have belt drive blower motors which have the
motor pulley factory set at four turns open.
For 208v operation on 208/230v rated direct drive units,
interchange motor leads to high speed for cooling and
medium speed for heating operation.
Table 9 shows the temperature rise at various airflow rates.
Tables 12 and 13 show both heating and cooling airflows at
various external static pressures. Refer to these tables to
determine the airflow for the system being installed. See
Tables 2 thru 7 for the rated heating and cooling airflows.
NOTE: Be sure that all supply- and return-air grilles are
open, free from obstructions, and adjusted properly.
A WARNING
Disconnect electrical power to the unit before changing
blower speed. (Be sure to turn off gas supply before dis¬
connecting electrical power.) Electrical shock can cause
personal injury or death.
13