Gas Pressure Adjustment
Gas Flow (Approximate)
1− Operate unit at least 15 minutes before checking gas flow. Determine the time in seconds for two revolu- tions of gas through the meter. (Two revolutions as- sures a more accurate time.) A portable LP gas meter (17Y44) is available for LP applications.
2− Divide the number of seconds by two and compare to the time in table 11. If manifold pressure is correct and rate is incorrect, check gas orifices for proper size and restriction.
3− Remove temporary gas meter if installed.
NOTE− To obtain accurate reading, shut off all other gas appliances connected to meter.
TABLE 11
GAS METER CLOCKING CHART
Unit | Seconds for One Revolution | |||||
Input | Natural |
| LP |
| ||
Rate | 1 cu ft | 2 cu ft |
| 1 cu ft |
| 2 cu ft |
(Btuh) | Dial | Dial |
| Dial |
| Dial |
75,000 | 48 | 96 |
| 120 |
| 240 |
|
|
|
|
|
|
|
125,000 | 29 | 58 |
| 72 |
| 144 |
|
|
|
|
|
|
|
130,000 | 28 | 55 |
| 69 |
| 138 |
|
|
|
|
|
|
|
235,000 | 15 | 31 |
| 38 |
| 77 |
|
|
|
|
|
|
|
260,000 | 14 | 28 |
| 35 |
| 69 |
|
|
|
|
|
|
|
470,000 | 8 | 15 |
| 19 |
| 38 |
|
|
|
|
|
|
|
Natural−1000 btu/cu ft | LP−2500 btu/cu ft |
| ||||
Note: Table assumes standard temperature (60°F), pressure (30in.Hg.), and fuel heating values (Btuh/Ft.3). Apply pressure corrections in altitudes above 2000 ft.
Gas Pressure
1 − Check the gas line pressure with the unit (both heat sec- tions) firing at the high heat input rate. A minimum of 4.5 in. w.c. for natural gas should be maintained.
2 − After the line pressure has been checked and ad- justed, check the high heat regulator pressure on both gas valves. See figure 20 for gas pressure adjustment screw location. The low heat setting is
TABLE 12
MANIFOLD GAS PRESSURES (HIGH HEAT)
| ALTITUDE | GAS | MANIFOLD PRESSURE | |
| feet (m) | FUEL | in. w.c. (kPa) | |
|
|
|
|
|
0 | − 2000 | (0 − 610) | Natural | 3.5 (0.87) |
|
|
|
|
|
2000 | − 4500 | (610 − 1372) | Natural | 3.5 (0.87) |
|
|
| ||
4500 − 7500* (1372 − | Natural | 3.2 (0.80) | ||
| 2286) |
|
| |
*In Canada, certification for installation at altitudes over 4500 feet (1372m) above sea level is the jurisdiction of the local authorities.
High Altitude Information
In Canada, certification for installation at altitudes over 4500 feet (1372m) above sea level is the jurisdiction of the local authorities.
See table 12 for the correct high heat manifold pressures to be maintained for natural gas.
Check the gas line pressure with the unit (both heat sections) firing at high heat input rate The minimum pressure as shown on the nameplate for natural gas must be main- tained.
No orifice change is required. No pressure switch change is required.
Other Unit Adjustments and Operation
Primary (S10 and S99) Limits
Each heat section has a primary limit located on the heat- ing compartment vestibule panel. These limits are facto- ry set and do not require field adjustment.
Flame Rollout Switches (S47 and S69)
Each heat section has a manually reset flame rollout switch. Each switch is located on the burner top plate. If tripped, a check for adequate combustion air should be made before resetting. The switches are
Combustion Air Pressure Switches (S18 and S45)
Each heat section has a combustion air pressure switch lo- cated on the heating compartment vestibule panel. Each switch checks for proper combustion air blower operation before allowing ignition trial. The switches are factory set and require no field adjustment.
Blower Motor Controls (K25 Circuit Board), (K20 Relay), (K123 Relay) and (K36 Relay)
When the gas valves are powered, the blower motor starts after a delay of 45 seconds. When the gas valves lose pow- er because the thermostat demand is satisfied, the blower motor remains running for 150 seconds. These timings are programmed into the K25 control board and are
If abnormal furnace operation causes either high limit (S10 or S99) to open, the relays K20, K123 and K36 maintain blower operation until the limit(s) is reset.
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