Bryant 574D - Manual (Page 19)

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use mercury or small dial--type thermometers because they are not
adequate for this type of measurement.
UNIT DAMAGE HAZARD
Failure to follow this caution may result in unit damage.
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.
! CAUTION
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. Liquid line temperature (°F (°C).
c. Discharge (high--side) pressure (psig).
5. Using “Cooling Charging Charts,” compare outdoor--air
temperature(°F (°C) db) with the discharge line pressure
(psig) to determine desired system operating liquid line
temperature (See Table 6).
6. Compare actual liquid line temperature with desired liquid
line temperature. Using a tolerance of ± 2°F (±1.1°C), add
refrigerant if actual temperature is more than 2°F (±1.1°C)
higher than proper liquid line temperature, or remove
refrigerant if actual temperature is more than 2°F (±1.1°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 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. For
heating operation, the airflow must produce a temperature
rise that falls within the range stamped on the unit rating
plate.
CAUTION
!
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 9 for wet coil pressure drop).
NOTE: Be sure that all supply--and return--air grilles are open,
free from obstructions, and adjusted properly. Airflow can be
changed using the User Interface.
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
Airflow can be changed by changing the lead connections of the
blower motor.
All 574D units are factor wired for low speed except sizes 030 and
048 which are wired for medium speed.
FOR 208/230V
For color coding on the 208/230V motor leads, see Table 5.
Table 5 – Color Coding for 208/230V Motor Lead s
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 contactor (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.
574D