Bryant 340MAV instruction manual III. Purge GAS Lines, IV. Adjustments, Set Gas Input Rate

III.PURGE GAS LINES

If not previously done, purge lines after all connections have been made and check for leaks.

WARNING: Never purge a gas line into a combustion chamber. Never use matches, candles, flame, or other sources of ignition for purpose of checking leakage. Use a soap-and-water solution to check for leakage. Failure to follow this warning could result in fire, explosion, per- sonal injury, or death.

IV. ADJUSTMENTS

A.Set Gas Input Rate

Furnace gas input rate on rating plate is for 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 of 2000 ft to 4500 ft 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 yearly heat value (at installed altitude) from local gas supplier.

b.Obtain average yearly specific gravity from local gas supplier.

→c. Verify furnace model and size. Table 8 can only be used for model 340MAV furnaces with heating sizes of 040 through 120. Table 9 can only be used for model 340MAV furnaces with a 140 heating size.

→d. Find installation altitude in Table 8 or 9.

→NOTE: For Canada altitudes of 2000 to 4500 ft, use U.S.A. altitudes of 2001 to 3000 ft in Table 8 or 9.

→e. Find closest natural gas heat value and specific gravity in Table 8 or 9.

f.Follow heat value and specific gravity lines to point of intersection to find orifice size and manifold pressure settings for proper operation.

EXAMPLE: (0Ð2000 ft altitude using Table 8)

Heating value = 1050 Btu/cu ft

Specific gravity = 0.62

Therefore: Orifice No. 45

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 cap that conceals adjustment screw for gas valve regulator. (See Fig. 44.)

c.Turn adjusting screw, counterclockwise (out) to decrease manifold pressure or clockwise (in) to increase manifold pressure.

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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. For altitudes above 2000 ft, the manifold pressure can be adjusted from 2.0 in. wc to 3.8 in. wc.

ON AND

OFF SWITCH

GAS

PRESSURE

REGULATOR

ADJUSTMENT

BURNER

ENCLOSURE

REFERENCE

PRESSURE

TAP

INLET

PRESSURE TAPMANIFOLD PRESSURE TAP

A95622

Fig. 44ÐRedundant Automatic Gas Valve

CAUTION: 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.

BURNER

ORIFICE

A93059

CAUTION: 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 burners and heat exchang- ers causing failures.

d.Replace gas valve regulator adjustment screw cap.

e.Replace burner enclosure front and verify adjusted gas input rate using method outlined in item 3.