Table 21 - Bryant 986TB Installation, Start-Up, Operating And Service And Maintenance Instructions

CAUTION
!
UNIT OPERATION HAZARD
Failure to follow this caution may result in intermittent unit
operation or performance satisfaction.
Condensate trap must be PRIMED or proper draining may
not occur. The condensate trap has two internal chambers
which can ONLY be primed by pouring water into the
inducer drain side of condensate trap.
1. Remove upper and middle collector box drain plugs oppos-
ite of the condensate trap. See Fig. 68.
2. Connect field-supplied 5/8−in. (16 mm) ID tube with at-
tached funnel to upper collector box drain connection. See
Fig. 68.
3. Pour one quart (liter) of water into funnel/tube. Water
should run through collector box, overfill condensate trap,
and flow into open field drain.
4. Remove funnel; replace collector box drain plug.
5. Connect field−supplied 5/8−in. (16mm) ID tube to middle
collector box drain port.
6. Pour one quart (liter) of water into funnel/tube. Water
should run through collector box, overfill condensate trap,
and flow into open field drain.
7. Remove funnel and tube from collector box and replace col-
lector box drain plug.
Purge Gas Lines
If not previously done, purge the lines after all connections have
been made and check for leaks.
WARNING
!
FIRE OR EXPLOSION HAZARD
Failure to follow this warning could result in personal
injury, death, and/or property damage.
Never purge a gas line into a combustion chamber. Never
test for gas leaks with an open flame. Use a commercially
available soap solution made specifically for the detection
of leaks to check all connections. A fire or explosion may
result causing property damage, personal injury or loss of
life.
Adjustments
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal
injury, death and/or property damage.
DO NOT bottom out gas valve regulator adjusting screw.
This can result in unregulated manifold pressure and result
in excess overfire and heat exchanger failures.
CAUTION
!
FURNACE DAMAGE HAZARD
Failure to follow this caution may result in reduced furnace
life.
DO NOT redrill orifices. Improper drilling (burrs,
out−of−round holes, etc.) can cause excessive burner noise
and misdirection of burner flames. This can result in flame
impingement of heat exchangers, causing failures. See Fig.
61.
For proper operation and long term reliability, the Furnace input
rate must be within +/−2 percent of input rate on furnace rating
plate, or as adjusted for altitude.
The gas input rate on rating plate is for installations at altitudes up
to 2000 ft. (609.6M).
NOTICE
The NATURAL GAS manifold pressure adjustments in Table
21 compensate for BOTH altitude AND gas heating value.
DO NOT apply an additional derate factor to the pressures
shown in Table 21. The values in this table are NOT
referenced to sea level; they are AS−MEASURED AT
ALTITUDE.
The heating content of natural gas at altitude may already
provide for a reduction in capacity of the furnace. Be sure to
obtain the expected in−season gas heating value of the gas
from the gas supplier BEFORE making any adjustments for
capacity or altitude. Refer to Table 21. No adjustments to the
furnace may be necessary at altitude for certain gas heating
values.
Refer to the instructions provided in the factory−specified
LP/Propane conversion kit for instructions for setting gas
manifold pressures for LP/Propane applications.
In the USA, the input rating for altitudes above 2000 ft. (609.6M)
must be reduced by 2 percent for each 1000 ft. (304.8M) above sea
level. Refer to Table 18. The natural gas manifold pressures in
Table 21 adjust for BOTH altitude and natural gas heating value.
In Canada, the input rating must be reduced by 5 percent for
altitudes of 2000 ft. (609.6M) to 4500 ft. (1371.6M) above sea
level. The natural gas manifold pressures in Table 21 adjust for
BOTH altitude and natural gas heating value.
NOTE: For Canadian altitudes of 2000 to 4500 ft. (609.6 to
1371.6M), Use USA altitudes of 2001 to 3000 ft. (609.6 to
914.4M).
To adjust manifold pressure to obtain the proper input rate, first,
determine if the furnace has the correct orifice installed. At higher
altitudes or different gas heat contents, it may be necessary to
change the factory orifice to a different orifice. Tables have been
provided in the furnace installation instructions to match the
required orifice to the manifold pressure to the heat content and
specific gravity of the gas. To do this:
1. Obtain average yearly gas heat value (at installed altitude)
from local gas supplier.
2. Obtain average yearly gas specific gravity from local gas
supplier.
3. Find installation altitude in Table 21.
4. Find closest natural gas heat value and specific gravity in

Table 21.

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