Airflow And Temperature Rise; Limit Switches; Auxiliary Limit Switch (Rollout); Start- -Up Cooling & Make Adjustments - Bryant 574B Installation Instructions Manual

HEATING NUMBER OF
INPUT (BTUH)* ORIFICES
40,000
60,000
90,000
115,000
130,000
* When a unit is converted to propane, different size orifices must be used. See separate, natural--to--propane conversion kit instructions.
† Based on altitudes from sea level to 2000 ft above sea level. For altitudes above 2000 ft, reduce input rating 4 percent for each additional 1000 ft above sea level.
In Canada, from 2000 ft above sea level to 4500 ft above sea level, de--rate the unit 10 percent.
Table 4 – Air Delivery (CFM) at Indicated Temperature Rise and Rated Heating Input
HEATING
INPUT
20
(BTUH)
40,000 1500
60,000 2250
90,000 —
115,000
—
130,000 —
NOTE: Dashed areas do not fall within the approved temperature rise range of the unit.

AIRFLOW AND TEMPERATURE RISE

The heating section for each size unit is designed and approved
for heating operation within the temperature- -rise range stamped
on the unit rating plate. Table 4 shows the approved temperature
rise range for each heating input, and the air delivery cfm at
various temperature rises. The heating operation airflow must
produce a temperature rise that falls within the approved range.
Refer to Indoor Airflow and Airflow Adjustments section to
adjust heating airflow when required.

LIMIT SWITCHES

Normally closed limit switch (LS) completes the control circuit
through the thermostat R circuit. Should the leaving- -air
temperature rise above the maximum allowable temperature, the
limit switch opens and the R control circuit "breaks." Any
interruption in the R control circuit instantly closes the gas valve
and stops gas flow to the burners and pilot. The blower motor
continues to run until LS resets.
When the air temperature at the limit switch drops to the
low- -temperature setting of the limit switch, the switch closes and
completes the R control circuit. The electric- -spark ignition
system cycles and the unit returns to normal heating operation.

AUXILIARY LIMIT SWITCH (ROLLOUT)

The function of the switch is to close the main gas valve in the
event of flame rollout. The switch is located above the main
burners. When the temperature at the auxiliary switch reaches the
maximum allowable temperature, the R control circuit trips,
closing the gas valve and stopping gas flow to the burners. The
indoor (evaporator) fan motor (IFM) and induced draft motor
continue to run until switch is reset. The IGC LED will display
FAULT CODE 7.
Table 3 – Heating Inputs
GAS SUPPLY PRESSURE (IN. WC)
Natural
Min
2 4.0
2 4.0
3 4.0
3 4.0
3 4.0
25 30 35
1200 1000 857
1800 1500 1286
— 2250 1929
— — 2464
— — 2786
Propane†
Max Min
13.0 4.0
13.0 4.0
13.0 4.0
13.0 4.0
13.0 4.0
TEMPERATURE RISE °F
40 45 50
750 667 600
1125 1000 900
1688 1500 1350
2156 1917 1725
2438 2167 1950
Step 4 — START- - UP COOLING AND MAKE
ADJUSTMENTS
!
UNIT DAMAGE HAZARD
Failure to follow this warning could result in unit component
damage.
Complete the required procedures given in the Pre- -Start- -Up
section before starting the unit. Do not jumper any safety
devices when operating the unit. Do not operate the
compressor when the outdoor temperature is below 55_F
(unless accessory low- -ambient kit is installed). Do not
rapid- -cycle the compressor. To prevent compressor damage
allow 5 minutes between "on" cycles.

CHECKING COOLING CONTROL OPERATION

Start and check the unit for proper cooling control operation as
follows:
1. Place room thermostat SYSTEM switch in OFF position.
Observe that blower motor starts when FAN switch is
placed in ON position and shuts down when FAN switch
is placed in AUTO. position.
2. Place SYSTEM switch in COOL position and FAN switch
in AUTO. position. Set cooling control below room
temperature. Observe that compressor, condenser fan, and
evaporator blower motors start. Observe that cooling cycle
shuts down when control setting is satisfied. The
evaporator fan will continue to run for the time selected on
the Easy Select board.
3. When using an auto- -changeover room thermostat, place
both SYSTEM and FAN switches in AUTO. positions.
Observe that unit operates in Heating mode when
temperature control is set to "call for heating" (above room
temperature) and operates in Cooling mode when
temperature control is set to "call for cooling" (below
room temperature).
19
MANIFOLD PRESSURE (IN. WC)
Max Natural
13.0 3.5
13.0 3.5
13.0 3.5
13.0 3.5
13.0 3.5
55 60 65
545 500 —
818 750 692
1227 1125 1038
1568 1438 1327
1773 1625 1500
WARNING
Propane†
3.5
3.5
3.4
3.7
3.5
70
—
—
964
1232
—