Carrier 58MTB Operations Instructions download pdf (Page 55)

3. Verify Natural Gas Input Rate By Clocking Gas Meter.

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. Calculate high-altitude adjustment (if required).

UNITED STATES

At altitudes above 2000 ft, this furnace has been approved

for 2 percent derate for each 1000 ft above sea level. See

Example and Table 15 for derate multiplier factor.

CANADA

At installation altitudes from 2001 to 4500 ft, this furnace

must be derated 5 percent by an authorized Gas Conversion

Station or Dealer. To determine correct input rate for

altitude, see example above and use 0.95 as derate multi-

plier factor.

b. Reinstall burner box cover.

NOTE: Clocking gas input rate MUST always be performed with

the burner box cover INSTALLED.

c. Check that gas valve adjustment caps are in place for

proper input to be clocked.

d. Obtain yearly heat value average 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

adjustment of gas heating value.

e. Check and verify orifice size in furnace. NEVER ASSUME

THE ORIFICE SIZE. ALWAYS CHECK AND VERIFY.

f. Turn off all other gas appliances and pilots.

g. Move setup switch SW-1 to ON position. This keeps

furnace locked in low-heat operation.

h. Jumper R-to-W/W1.

i. Let furnace run for 3 minutes in low-heat operation.

j. Measure time (in sec) for gas meter to complete 1 revolu-

tion. Note reading.

k. Refer to Table 16 for cubic ft of gas per hr.

l. Multiply gas rate cu ft/hr by heating value (Btu/cu ft).

m. Move setup switch SW-1 to OFF position and jumper R

and W1 and W2 thermostat connections. This keeps

furnace locked in high-heat operation. Repeat items ’i’

through ’l’ for high-heat operation.

EXAMPLE: (0-2000 ft altitude)

Furnace input from rating plate is 100,000 Btuh.

Btu heating input = Btu/cu ft X cu ft/hr

Heating value of gas = 975 Btu/cu ft

Time for 1 revolution of 2-cu ft dial = 70 sec

Gas rate = 103 cu ft/hr (from Table 16)

Btu heating input = 103 X 975 = 100,425 Btuh. In this

example, the orifice size and manifold pressure adjustment

is within ±2 percent of the furnace input rate.

NOTE: Measured gas inputs (high-heat and low-heat) must be

within ±2 percent of that stated on furnace rating plate when

installed at sea level or derated per that stated above when installed

at higher altitudes.

n. Remove jumper across R, W/W1, and W2 thermostat

connections to terminate call for heat.

Fig. 51—Redundant Automatic Gas Control Valve

A97358

ON/OFF

SWITCH

INLET

PRESSURE

TAP

MANIFOLD

PRESSURE

TAP

LOW-FIRE

ADJUSTMENT

ALLEN SCREW

(UNDER CAP)

HIGH-FIRE

ADJUSTMENT

ALLEN SCREW

(UNDER CAP)

Fig. 52—Burner Flame

A89020

BURNER FLAME

BURNER

MANIFOLD

Fig. 53—Burner Orifice

A93059

BURNER

ORIFICE

EXAMPLE:

100,000 Btuh input furnace installed at 4300 ft.

Derate Furnace Input Rate

Furnace Input Rate X Multiplier = at Installation

at Sea Level Factor Altitude

100,000 X 0.91 = 91,000

1 2 ... 50 51 52 53 54 55 56 57 58 59 60

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Carrier 58MTB Operations Instructions Page 55

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