024 through 060 Models
The charging chart (see Table 6A) includes the required suction
line temperature at given suction line pressures and outdoor ambient
temperatures.
An accurate superheat thermocouple or thermistor-type
thermometer 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.
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 (°C)db).
b. Evaporator inlet-air temperature (°F (°C) wb.
c. Suction-tube temperature (°F (°C) at low-side service
fitting.
d. Suction (low-side) pressure (psig).
5. Using "Cooling Charging Charts," compare outdoor-air
temperature(°F (°C) db) with the suction line pressure (psig)
to determine desired system operating suction line
temperature. (See Fig. Table 6A.)
6. Compare actual suction-tube temperature with desired
suction-tube temperature. Using a tolerance of .+ 3°F
(-+1.7°C), add refrigerant if actual temperature is more than
3°F (1.7°C) higher than proper suction-tube temperature,
or remove refrigerant if actual temperature is more than 3°F
(1.7°C) lower than required liquid line temperature.
NOTE: If the problem causing the inaccurate readings is a
refrigerant leak, refer to the Check for Refrigerant Leaks section.
INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
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. For
heating operation, the airflow must produce a temperature rise
that falls within the range stamped on the unit rating plate.
Table 8 shows the temperature rise in each heating mode. Refer to
these tables to determine the desired heating airflow for the system
being installed. (See Table 7 for filter pressure drop and Table 9 for
wet coil pressure drop).
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.
Airflow can be changed by changing the lead connections of the
blower motor.
All 48SD units are factor wired for low speed except the 030
through the 048 size.
For color coding on the motor leads, see Table 5.
Table 5--Color Coding for Motor Leads
Black = High Speed
Blue = Medium Speed
Red = Low Speed
To change the speed of the indoor fan motor (IFM), remove the fan
motor speed leg lead from the blower relay (BR). This wire is
attached to terminal blower motor (BM) of the integrated gas control
(IGC) board for single-phase units. To change the speed, remove
and replace with lead for desired blower motor speed. Insulate the
removed lead to avoid contact with chassis parts.
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:
1. 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.
2. The normally open contacts of energized contacmr (C) close
and complete the circuit through compressor motor (COMP)
to condenser (outdoor) fan motor (OFM). Both motors start
instantly.
3. The set of normally open contacts of energized relay BM
close and complete the circuit through evaporator blower
(indoor) fan motor (IFM).
NOTE: Once the compressor has started and then 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. The condenser and compressor motors stop. After
a 30-sec. delay, the blower motor stops. The unit is in a standby
condition, waiting for the next call for cooling from the room
thermostat.
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