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Gas Supply Pressure
Gas supply pressure should be within minimum and maximum
values listed on rating plate (minimum and maximum pressures,
refer to Table 5). Pressures are usually set by gas suppliers.
Manifold Gas Pressure Adjustment
NOTE:
Make adjustment to manifold pressure with burners
operating.
1. Remove the burner compartment door.
2. Remove the blower compartment door. Place a jumper
across furnace controls R to W. Replace blower compart-
ment door.
3. With gas OFF, connect manometer to tapped opening on
gas valve. Use manometer with a 0 to 15 inches of water
column range.
4. Turn gas ON and remove adjustment screw cover on gas
valve. Turn adjusting screw counterclockwise to decrease
manifold pressure and clockwise to increase pressure.
NOTE: Adjustment screw cover MUST be replaced on gas
control valve before reading manifold pressure and operating
furnace.
5. Set manifold pressure to value as shown in Table 6 or 7
under GAS SUPPLY AND PIPING section in this manu-
al.
6. When the manifold pressure is properly set, replace the ad-
justment screw cover on the gas control valve.
Regulator Adjustment
Under Cap
INLET
Inlet
Pressure
1
Tap
/
NPT
8
Fig. 46 - - Typical Gas Valve
7. Remove blower compartment door. Remove jumper wire
from thermostat connection on furnace control board. Re-
move manometer connection from manifold pressure tap,
and replace plug in manifold.
8. Check for leaks at plug.
9. Replace the burner and blower compartment doors.
Natural Gas Input Rating Check
NOTE: The gas meter can be used to measure input to furnace.
Rating is based on a natural gas BTU content of 1,000 BTU's per
cubic meter. Check with gas supplier for actual BTU content.
1. Turn OFF gas supply to all appliances and start furnace.
Use jumper wire on R to W for Heat.
2. Time how many seconds it takes the smallest dial on the
gas meter to make one complete revolution. Refer to
Example.
NOTE: If meter uses a 2 cubic foot dial, divide results
(seconds) by two.
Natural Gas
BTU Content
1,000
3. Remove jumper wire from R to W.
4. Relight all appliances and ensure all pilots are operating.
Main Burner Flame Check
Allow the furnace to run approximately 10 minutes then inspect
the main burner. See Fig. 47.
Check for the following (Fig. 47):
S Stable and blue flames. Dust may cause orange tips or wisps of
yellow, but flames MUST NOT have solid, yellow tips.
S Flames extending directly from burner into heat exchanger.
S Flames do NOT touch sides of heat exchanger
If any problems with main burner flames are noted, it may be
necessary to adjust gas pressures, or check for drafts.
Outlet
Pressure
Tap
1
/
NPT
8
NOTE: For igniter location see Fig. 48.
OUTLET
1/
2
(52.4)
16
5
/
(8)
16
A07732
NOTE: Flame sensor has a different orientation in all 050 models.
Temperature Rise Check
The blower speed MUST be set to give the correct air
temperature rise through the furnace as marked on the rating
plate. Temperature rise is the difference between supply and
return air temperatures.
To check temperature rise,use the following procedure:
1.Place thermometers in supply and return air registers as close to
furnace as possible, avoiding direct radiant heat from heat
exchangers.
2.Operate furnace continuously for 15 minutes with all registers
and duct dampers open.
3.Take reading and compare with range specified on rating plate.
4.If the correct amount of temperature rise is NOT obtained, it
may be necessary to change blower speed. A higher blower speed
41
Example
No. of
Time Per
Seconds
Cubic Foot in
Per Hour
Seconds
3,600
48
1,000 x 3,600 ÷ 48 = 75,000 BTUH
Burner Face
Fig. 47 - - Main Burner
Fig. 48 - - Igniter Location
BTU Per
Hour
75,000
.
A07734
1
/
(6.4)
4
A07735
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