Adjust Gas Input; Cooling; Heating; Safety Relief - Bryant 548D Installation, Start-Up And Service Instructions Manual

NOTE: When the compressor is rotating in the wrong direc-
tion, the unit makes an elevated level of noise and does not
provide heating/cooling.
IX. ADJUST GAS INPUT
The gas input to the unit is determined by measuring the
gas flow at the meter or by measuring the manifold pressure.
Manifold pressure should be 3.5 in. wg.
X. COOLING
To start unit, turn on main power supply. Set system selector
switch at COOL position and fan switch at AUTO position.
Adjust thermostat to a setting below room temperature.
Compressor indoor and outdoor fans start on closure of
contactors.
Check unit charge. Refer to Refrigerant Charge section on
page 32. Unit must operate for at least 15 minutes before
adjusting charge.
Reset thermostat at a position above room temperature.
Compressor and outdoor fans will shut off.
To Shut Off Unit
Set system selector switch at OFF position. Resetting ther-
mostat at a position above room temperature shuts unit off
temporarily until space temperature exceeds thermostat
setting.
Compressor restart is accomplished by manual reset at the
thermostat by turning the selector switch to OFF position
and then ON position.
XI. HEATING
To start unit, turn on main power supply.
Set thermostat at HEAT position and a setting above room
temperature, fan at AUTO position.
First stage of thermostat energizes the indoor fan motor,
compressor, and outdoor fan; second stage energizes electric
heater elements if installed. Check heating effects at air sup-
ply grille(s).
If accessory electric heaters do not energize, reset limit
switch (located on indoor-fan scroll) by depressing button
located between terminals on the switch.
To Shut Unit Off
Set system selector switch at OFF position. Resetting heat-
ing selector lever below room temperature temporarily shuts
unit off until space temperature falls below thermostat
setting.
XII. SAFETY RELIEF
A soft solder joint in the suction line at the loss-of-charge/
low-pressure switch fitting provides pressure relief under
abnormal temperature and pressure conditions.
XIII. VENTILATION (CONTINUOUS FAN)
Set fan and system selector switches at ON and OFF posi-
tions, respectively. Indoor fan operates continuously to pro-
vide constant air circulation.
XIV. OPERATING SEQUENCE
A. Cooling, Units Without Economizer
When the thermostat calls for cooling, terminals G and Y1
are energized. The indoor fan contactor (IFC), outdoor fan
contactor (OFC), RVS1 (reversing valve solenoid), and
compressor contactor no. 1 (C1) are energized and the
indoor-fan motor, compressor no. 1, outdoor-fan motors and
outdoor fans start. The outdoor-fan motors run continuously
while unit is cooling. If the thermostat calls for a second
stage of cooling by energizing Y2, compressor contactor no. 2
(C2) and RVS2 are energized and compressor no. 2 starts.
B. Heating, Units Without Economizer
Upon a call for heating through terminal W1, IFC, OFC, C1,
and C2 are energized. On units equipped for 2 stages of heat,
when additional heat is needed, HC is energized through
W2.
C. Cooling, Units With Durablade Economizer
When the outdoor-air temperature is above the OAT setting
and the room thermostat calls for cooling, the compressor
contactor no. 1 and outdoor fan contactor (OFC) are ener-
gized to start compressor no. 1 and outdoor-fan motors.
RVS1 (reversing valve solenoid) is energized). The indoor-fan
motor (IFM) is energized and the economizer damper moves
to the minimum position. Upon a further call for cooling,
compressor contactor no. 2 will be energized, starting com-
pressor no. 2. RVS2 is energized. After the thermostat is sat-
isfied and the IFM is deenergized, the damper moves to the
fully closed position.
When the outdoor-air temperature is below the OAT setting
and the thermostat calls for Y1 and G, the economizer
damper moves to the minimum position when the indoor fan
starts. The first stage of cooling is provided by the econo-
mizer. If the supply-air temperature is above 57 F, a switch
on the supply-air thermostat is closed between the T2 ter-
minal and the 24 vac terminal. This causes the damper to
continue to modulate open until the supply-air temperature
falls below 55 F or the damper reaches the fully open
position.
When the supply-air temperature is between 55 F and 52 F,
the supply-air thermostat has open switches between the T2
and 24 vac terminals and between the T1 and 24 vac termi-
nals. This causes the economizer damper to remain in an
intermediate open position.
If the supply-air temperature falls below 52 F, a switch on
the supply-air thermostat is closed between the T1 terminal
and the 24 vac terminal. This causes the damper to modu-
late closed until the supply-air temperature rises above 55 F
or the damper reaches the minimum position.
When the supply-air temperature is between 55 F and 57 F,
the supply-air thermostat has open switches between the T2
and 24 vac terminals. This causes the economizer damper to
remain in an intermediate open position.
If the outdoor air alone cannot satisfy the cooling require-
ments of the conditioned space, economizer cooling is in-
tegrated with mechanical cooling, providing second stage
cooling. Compressor no. 1 and outdoor fans will be ener-
gized, and the position of the economizer damper will be
determined by the supply-air temperature. Compressor no. 2
is locked out.
When the second stage of cooling is satisfied, the compressor,
RVS2, and outdoor fan motors will be deenergized. The
damper position will be determined by the supply-air
temperature.
When the first stage of cooling is satisfied, the damper will
move to fully closed position.
— 29 —