Bryant CONDENSING GAS FURNACE 355MAV Installation, Start-Up, And Operating Instructions Manual Download Page 48

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NOTE:

Clocking gas input rate MUST always be performed with

the burner box cover INSTALLED.

c. Check that gas valve adjustment caps are in place for

proper input to be clocked.

d. Obtain average heat value (at altitude) from local gas

supplier.

NOTE:

Be sure heating value of gas used for calculations is

correct for your altitude. Consult local gas utility for altitude
adjustment of gas heating value.

e. Check and verify orifice size in furnace. NEVER AS-

SUME THE ORIFICE SIZE. ALWAYS CHECK AND
VERIFY.

f. Turn off all other gas appliances and pilots.

g. Turn setup switch SW1-2 to ON position. (See Fig. 32.)

This keeps furnace locked in low-heat operation.

h. Jumper R-to-W/W1.

i. Let furnace run for 3 minutes in low-heat operation.

j. Measure time (in sec) for gas meter to complete 1

revolution. Note reading.

k. Refer to Table 13 for cubic ft of gas per hr.

l. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).

m. Turn setup switch SW1-2 to OFF position and jumper R

and W/W1 and W2 thermostat connections. (See Fig.
32.) This keeps furnace locked in high-heat operation.
Repeat items i through l for high-heat operation.

EXAMPLE: (High-heat operation at 0—2000 ft altitude)
Furnace input from rating plate is 100,000 Btuh
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 975 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 70 sec
Gas rate = 103 cu ft/hr (from Table 13)
Btu heating input = 103 X 975 = 100,425 Btuh
In this example, the orifice size and manifold pressure
adjustment is within

2 percent of the furnace input rate.

NOTE:

Measured gas inputs (high heat and low heat) must be

within

2 percent of that stated on furnace rating plate when

installed at sea level or derated per that stated above when installed
at higher altitudes.

n. Remove jumper across R, W/W1, and W2 thermostat

connections to terminate call for heat.

Set Temperature Rise

CAUTION:

UNIT DAMAGE HAZARD

Failure to follow this caution may result in overheating
the heat exchangers or condensing flue gases in heat
exchanger areas not designed for condensate.
Temperature rise must be within limits specified on unit
rating plate. Operation is within a few degrees of mid-
point of rise range when setup switch SW1-4 is OFF.

Furnace must operate within ranges of temperature rise specified
on the furnace rating plate. Determine air temperature rise as
follows:

1. Place thermometers in return and supply ducts as near

furnace as possible. Be sure thermometers do not see heat
exchanger so that radiant heat does not affect readings. This
practice is particularly important with straight-run ducts.

2. When thermometer readings stabilize, subtract return-air

temperature from supply-air temperature to determine air
temperature rise.

NOTE:

Temperature rise can be determined for low-heat opera-

tion by placing setup switch SW1-2 on furnace control in ON
position. For high-heat operation, place setup switch SW1-2 in
OFF position and jumper R-W2 on furnace control. DO NOT
forget to return setup switch to OFF position and remove R-W2
jumper upon completion of testing. (See Fig. 32 for switch and
terminal location.)

3. This furnace is capable of automatically providing proper

airflow to maintain the temperature rise within the range
specified on furnace rating plate. If temperature rise is
outside this range, proceed as follows:

a. Check gas input for low- and high-heat operation.

TABLE 12—ALTITUDE DERATE MULTIPLIER FOR U.S.A.

ALTITUDE

(FT)

% OF

DERATE

DERATE MULTIPLIER

FACTOR

0—2000

1.00

2001—3000

4—6