Bryant 310AAV Furnace Damage Hazard, Never Assume Orifice SIZE. Always Check and Verify

!CAUTION

FURNACE DAMAGE HAZARD

Failure to follow this caution may result in reduced furnace life.

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 heat exchangers, causing failures. (See Fig. 43.)

Furnace gas input rate on rating plate is for installations at altitudes up to 2000 ft. (610 M). Furnace input rate must be within +/-2 percent of furnace rating plate input.

1.Determine the correct gas input rate.

The input rating for altitudes above 2,000 ft. (610 M) must be reduced by 4 percent for each 1,000 ft. (305 M) above sea level. For installations below 2000 ft., refer to the unit rating plate. For installations above 2000 ft. (610 M), mul- tiply the input on the rating plate by the derate multiplier in Table 11 for the correct input rate.

2.Determine the correct orifice and manifold pressure adjust- ment. There are two different orifice and manifold adjust- ment tables. All models in all positions, except Low NOx models in downflow or horizontal positions, use Table 15 (22,000 Btuh/Burner).

Low NOx models in the downflow or horizontal positions must use Table 16 (21,000 Btuh/Burner). See input listed on rating plate.

a.Obtain average yearly gas heat value (at installed alti- tude) from local gas supplier.

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

c.Find installation altitude in Table 15 or 16.

d.Find closest natural gas heat value and specific gravity in Table 15 or 16.

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

f.Check and verify burner orifice size in furnace.

NEVER ASSUME ORIFICE SIZE. ALWAYS CHECK AND VERIFY.

g.Replace orifice with correct size if required by Table 15 or 16. Use only factory-supplied orifices. See EXAMPLE 2.

EXAMPLE 2: (0-2000 ft. (0-610 M) altitude)

For 22,000 Btuh per burner application use Table 15. Heating value = 1000 Btuh/cu ft.

Specific gravity = 0.62 Therefore: Orifice No. 43* Manifold pressure: 3.7-In. W.C.

*Furnace is shipped with No. 43 orifices. In this example all main burner orifices are the correct size and do not need to be changed to obtain proper input rate.

3.Adjust manifold pressure to obtain correct input rate.

a.Turn gas valve ON/OFF switch to OFF.

b.Remove manifold pressure tap plug from gas valve. (See Fig. 42.)

c.Connect a water column manometer or similar device to manifold pressure tap.

d.Turn gas valve ON/OFF switch to ON.

e.Manually close blower door switch.

f.Set thermostat to call for heat.

g.Jumper R and W thermostat connections on furnace control board to start furnace.

h.Remove regulator seal cap and turn regulator adjusting screw counterclockwise (out) to decrease input rate of clockwise (in) to increase input rate.

i.Install regulator seal cap.

j.Leave manometer or similar device connected and proceed to Step 4.

NOTE: DO NOT set manifold pressure less than 3.2-In. W.C. or more than 3.8-In. W.C. for natural gas at sea level. If manifold pressure is outside this range, change main burner orifices or refer Table 15 or 16.

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.

4. Verify natural gas input rate by clocking meter.

NOTE: Gas valve regulator adjustment cap must be in place for proper input to be clocked.

a.Turn off all other gas appliances and pilots served by the meter.

b.Run furnace for 3 minutes in heating operation.

c.Measure time (in sec) for gas meter to complete 1 re- volution and note reading. The 2 or 5 cubic feet dial provides a more accurate measurement of gas flow.

d.Refer to Table 13 for cubic ft. of gas per hr.

e.Multiply gas rate (cu ft./hr) by heating value (Btu/cu ft.) to obtain input.

If clocked rate does not match required input from Step 1, increase manifold pressure to increase input or decrease manifold pressure to decrease input. Repeat steps b through e until correct input is achieved. Reinstall regulator seal cap on gas valve.

5.Set temperature rise. The furnace must operate within the temperature rise ranges specified on the furnace rating plate. Do not exceed temperature rise range specified on unit rating plate. Determine the temperature rise as fol- lows:

NOTE: Blower access door must be installed when taking temperature rise reading. Leaving blower access door off will result in incorrect temperature measurements.

a.Place thermometers in return and supply ducts as close to furnace as possible. Be sure thermometers do not see radiant heat from heat exchangers. Radiant heat affects temperature rise readings. This practice is par- ticularly important with straight-run ducts.

b.When thermometer readings stabilize, subtract return- air temperature from supply-air temperature to determ- ine air temperature rise.

NOTE: Blower access door must be installed for proper temperature rise measurement.

NOTE: If the temperature rise is outside this range, first check:

SGas input for heating operation. S Derate for altitude if applicable.

SReturn and supply ducts for excessive restrictions caus- ing static pressures greater than 0.50-In. W.C.

SDirty filter.

310AAV

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