Operating instructions
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A99119
Fig. 56--Filling Condensate Trap
Step 3--Purge Gas Lines
If not previously done, purge lines after all connections have been
made and check for leaks.
d. Find installation altitude in Table 9 or I0.
NOTE: For Canadian altitudes of 2001 to 4500 It, use U.S.A.
altitudes of 2001 to 3000 ft in Table 9 or 10.
e. Find closest natural gas heat value and specific gravity in
Table 9 or i0.
f. Follow heat value and specific gravity lines to point of
intersection to find orifice size and manifold pressure
settings for proper operation.
EXAMPLE: (0-2000 ft altitude using Table 9)
Heating value 1050 Btuicu ft
Specific gravity 0.62
Therefore: Orifice No. 45 and
Manifbld pressure 3.6-in. wc
* Furnace is shipped with No. 45 orifices. In this
example all main burner orifices are the correct size
and do not need to be changed to obtain the proper
input rate.
Check and verify burner orifice size in furnace. NEVER ASSUME
ORIFICE SIZE; ALWAYS CHECK AND VERIFY.
2. Adjust manifold pressure to obtain input rate.
NOTE: Manifold pressure must ahvays be measured with burner
enclosure front REMOVED. Gas meter must always be clocked
with burner enclosure front INSTALLED.
a. Remove burner enclosure front.
b. Remove seal cap that conceals adjustment screw for gas
valve regulator. (See Fig. 57.)
c. Jumper R and W thermostat connections on control to start
furrlace.
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. Failure to follow this warning
could result in fire, explosion, personal injury, or death.
Step 4--Adjustments
SET GAS INPUT RATE
Furnace gas input rate on rating plate is fbr installations at altitudes
up to 2000 ft.
In the U.S.A., the input ratings for altitudes above 2000 ft must be
reduced by 2 percent for each 1000 ft above sea level.
In Canada, the input ratings must be derated by 5 percent for
altitudes between 2001 ft to 4500 ft above sea level.
Furnace input rate must be within ± 2 percent of input on furnace
rating plate adjusted for altitude.
i. Determine natural gas orifice size and manifold pressure for
correct mput.
a. Obtain average gas heat value (at installed altitude) fi'om
local gas supplier.
b. Obtain average gas specific gravity from local gas supplier.
c. Verify furnace model and size. Table 9 can only be used for
model 58MXA furnaces with rating plate heating inputs
(1000's Btuh) of 040 through 120. Table 10 can only be
used for model 58MXA fumaces with a heating size of 140.
40
A00238
Fig. 57--Redundant Automatic Gas Control Valve
d. Turn adjusting screw, counterclockwise (out) to decrease
manilbld pressure or clockwise (in) to increase manifold
pressure.