Carrier 58MEB Installation, Start-Up, And Operating Instructions Manual page 55

In Canada, the input ratings must be derated by 5 percent for
altitudes between 2001 ft to 4500 ft (1524.3 to 1371.6 M) above
sea level.
Furnace input rate must be within ± 2 percent of input on furnace
rating plate adjusted for altitude.
1. Determine natural gas orifice size and manifold pressure
for correct input.
a. Obtain average gas heat value (at installed altitude)
from local gas supplier.
b. Obtain average gas specific gravity from local
gas supplier.
c. Verify furnace model and size. Table 13 can only be
used for model 58MEB furnaces with rating plate
heating inputs (1000's Btuh) of 040 through 120.
d. Find installation altitude in Table 13.
NOTE: For Canadian altitudes of 2001 to 4500 ft (609.9 to
1371.6 M), use U.S.A. altitudes of 2001 to 3000 ft (609.9 to
914.4 M) in Table 13.
e. Find closest natural gas heat value and specific gravity
in Table 13 or 14.
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 (0 - - 609.9 M) altitude using Table 13)
Heating value = 1050 Btu/cu ft
Specific gravity = 0.62
Therefore: Orifice No. 45 and
Manifold 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 always 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. 55.)
c. Jumper R and W thermostat connections on control to
start furnace.
d. Turn adjusting screw, counterclockwise (out) to
decrease manifold pressure or clockwise (in) to
increase manifold pressure.
NOTE: This furnace has been approved for a manifold pressure
of 3.2 in. wc to 3.8 in. wc when installed at altitudes up to 2000 ft
(609.6 M). For altitudes above 2000 ft (609.6 M), the manifold
pressure can be adjusted from 2.0 in. wc to 3.8 in. wc. If manifold
pressure is outside this range, change burner orifices to obtain
pressure in this range.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in reduced
furnace life.
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.
NOTE: If orifice hole appears damaged or it is suspected to have
been redrilled, check orifice hole with a numbered drill bit of
correct size. Never redrill an orifice. A burr-free and squarely
aligned orifice hole is essential for proper flame characteristics.
ON/OFF Switch
½ " NPT Inlet
1/8 NPT Inlet
Pressure Tap
Fig. 55 - - Redundant Automatic Gas Control Valve
Fig. 56 - - Orifice Holes
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in component
damage.
DO NOT redrill orifices. Improper drilling (burrs, out-of
round holes, etc.) can cause excessive burner noise and
misdirection of burner flames. (See Fig. 56.)
- - 55 - -
Regulator Seal Cap
Regulator Adjustment
Under Cap
½" NPT Outlet
1/8" NPT Manifold
Pressure Tap
A07536
BURNER
ORIFICE
A93059