Carrier 58MCA Installation, Start-Up, And Operating Instructions Manual page 32

Fig. 43—Inducer Housing Drain Tube
EXAMPLE:
Heating value = 1010 Btu/cu ft
Specific gravity = 0.62 Therefore: Orifice No. 44* with
manifold pressure 3.3-in. wc * Furnace is shipped with No.
45 orifices. In this example all main burner orifices must be
changed and manifold pressure adjusted.
Check and verify orifice size in furnace. NEVER ASSUME
ORIFICE SIZE; ALWAYS CHECK AND VERIFY.
Proceed to item 3. to adjust manifold pressure.
2. Determine natural gas input rate by clocking gas meter then
adjust manifold pressure per item 3.
NOTE: Be sure all pressure tubing, combustion-air and vent
pipes, and burner enclosure front are in place when checking input
by clocking gas meter.
a. Obtain average yearly heat value for local gas supply.
NOTE: Be sure heating value of gas used for calculations is
correct for your altitude. Consult local gas utility for altitude
adjustments of gas heating value. Turn off all other gas appliances
and pilots.
b. Start furnace and let run for 3 minutes.
c. Measure time (in sec) for gas meter test dial to complete 1
revolution.
d. Refer to Table 8 for cubic ft of gas per hr.
e. Multiply gas rate (cu ft/hr) X heating value (Btu/cu ft).
Obtain heating value from local gas utility.
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Fig. 44—Filling Condensate Trap
EXAMPLE:
Btu heating input = Btu/cu ft X cu ft/hr
Heating value of gas = 1010 Btu/cu ft
Time for 1 revolution of 2-cu ft dial = 72 sec
Gas rate = 100 cu ft/hr (from Table 8)
Btu heating input = 100 X 1010 = 101,000 Btuh
In this example, the orifice size and manifold pressure
adjustment is within ±2 percent of the furnace input rate.
NOTE: High altitude—Gas input on rating plate is for altitudes
up to 2000 ft. Ratings for altitudes over 2000 ft must be 4 percent
less for each 1000 ft above sea level. To obtain altitude adjusted
rating, adjust manifold pressure (see item 3) and replace main
burner orifices as needed. Refer to NFGC Appendix F, Table F-4
for proper orifice sizing at high altitudes.
NOTE: In Canada installation applications from 2000 to 4500 ft
above sea level are derated 10 percent from Conversion Station.
f. Proceed to item 3. to adjust manifold pressure.
3. Adjust gas input.
NOTE: Manifold pressure must always be measured with burner
enclosure front REMOVED. Gas meter must always be clocked
with burner enclosure front INSTALLED. Gas valve has been
nominally set at 3.5-in. wc for natural gas.
a. Remove burner enclosure front and cap that conceals
adjustment screw for gas valve regulator. (See Fig. 45.)
b. Turn adjusting screw either counterclockwise (out) to
decrease input rate or clockwise (in) to increase rate. When
adjusting input rate, DO NOT set manifold pressure less
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