SERVICE AND TECHNICAL SUPPORT MANUAL Gas Furnace: (F/G)9MAC
Specifications subject to change without notice.
440 04 4201 01 5
Figure 1 Priming Condensate Drain
L11F065
Representative drawing only, some models may vary in appearance.
Purge Gas Lines
If not previously done, purge the lines after all connections
have been made and check for leaks.
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.
!
WARNING
Adjustments
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.
!
WARNING
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 Figure 2)
CAUTION
!
Figure 2 Orifice Hole
A93059
BURNER
ORIFICE
For proper operation and long term reliability, the Furnace input
rate must be within +2 percent of input rate on furnace rating
plate.
The gas input rate on rating plate is for installations at altitudes
up to 2000 ft. (609.6M).
In the USA., the input rating for altitudes above 2000 ft. (610 M)
must be reduced by 2 percent for each 1000 ft. (304.8M) above
sea level refer to Table 1.
In Canada, the input rating must be derated by 5 percent for
altitudes of 2000 ft. (610 M) to 4500 ft. (1372 M) above sea
level.
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:
a. Obtain average heat value (at installed altitude) from
local gas supplier.
b. Obtain average specific gravity from local gas supplier.
c. Find installation altitude range for your installation in the
manifold pressure tables. (See Table 3)
d. Find closest natural gas heat value and specific gravity in
Table 3.
e. Follow heat value and specific gravity lines to point of
intersection to find orifice size and maximum and
minimum manifold pressure settings for proper operation.
f. Check and verify burner orifice size in furnace. Never
assume orifice size. Always check and verify.
g. Replace orifice with correct size, if required by Table 3.
Use only factory−supplied orifices. See EXAMPLE.
EXAMPLE: 0 − 2000 ft. (0 − 609.6M) altitude
Heating value = 1050 Btu/cu ft.
Specific gravity = 0.62
Therefore: Orifice No. 44
Manifold pressure: 3.4−in. w.c. for maximum heat, 0.55−in. w.c.
for minimum heat.
* Furnace is shipped with No. 44 orifices. In this example, all
main burner orifices are the correct size and do not need to be
changed to obtain proper input rate.
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