4 - Move gas valve switch to OFF.
5 - Replace the upper access panel.
Failure To Operate
If the unit fails to operate, check the following:
1 - Is the thermostat calling for heat?
2 - Are access panels securely in place?
3 - Is the main disconnect switch closed?
4 - Is there a blown fuse or tripped breaker?
5 - Is the filter dirty or plugged? Dirty or plugged filters will cause the limit control to shut the unit off.
6 - Is gas turned on at the meter?
7 - Is the manual main shut‐off valve open?
8 - Is the internal manual shut‐off valve open?
9 - Is the unit ignition system in lockout? If the unit locks out again, inspect the unit for blockages.
Heating Sequence Of Operation
1 - When thermostat calls for heat, combustion air inducer starts.
2 - Combustion air pressure switch proves blower opera tion. Switch is factory set and requires no adjustment.
3 - After a
4 - After a
5 - Gas is ignited, flame sensor proves the flame, and the combustion process continues.
6 - If flame is not detected after first ignition trial, the igni tion control will repeat steps 3 and 4 four more times before locking out the gas valve (“WATCHGUARD” flame failure mode). The ignition control will then auto matically repeat steps 1 through 6 after 60 minutes.
To interrupt the
Gas Pressure Adjustment
Gas Flow (Approximate)
TABLE 10
GAS METER CLOCKING CHART
| Seconds for One Revolution | |||||
|
|
|
|
|
|
|
ML193 | Natural |
| LP |
| ||
Unit | 1 cu ft | 2 cu ft |
| 1 cu ft |
| 2 cu ft |
| Dial | Dial |
| Dial |
| DIAL |
|
|
|
|
|
|
|
80 | 160 |
| 200 |
| 400 | |
|
|
|
|
|
|
|
55 | 110 |
| 136 |
| 272 | |
|
|
|
|
|
|
|
41 | 82 |
| 102 |
| 204 | |
|
|
|
|
|
|
|
33 | 66 |
| 82 |
| 164 | |
|
|
|
|
|
|
|
27 | 54 |
| 68 |
| 136 | |
|
|
|
|
|
|
|
| ||||||
Furnace should operate at least 5 minutes before checking gas flow. Determine time in seconds for two revolutions of gas through the meter. (Two revolutions assures a more accurate time.) Divide by two and compare to time in table 10 below. If manifold pressure matches table 11 and rate is incorrect, check gas orifices for proper size and restriction. Remove temporary gas meter if installed.
NOTE - To obtain accurate reading, shut off all other gas appliances connected to meter.
Supply Pressure Measurement
When testing supply gas pressure, use the 1/8” N.P.T. plugged tap or pressure post located on the gas valve to facilitate test gauge connection. See figure 61. Check gas line pressure with unit firing at maximum rate. Low pres sure may result in erratic operation or underfire. High pres sure can result in permanent damage to gas valve or over fire.
On multiple unit installations, each unit should be checked separately, with and without units operating. Supply pres sure must fall within range listed in table 11.
Manifold Pressure Measurement
1 - Remove the threaded plug from the outlet side of the gas valve and install a
2 - Start unit and allow 5 minutes for unit to reach steady state.
3 - While waiting for the unit to stabilize, observe the flame. Flame should be stable and should not lift from burner. Natural gas should burn blue.
4 - After allowing unit to stabilize for 5 minutes, record manifold pressure and compare to value given in table 11.
NOTE - Shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to remove barbed fitting and replace threaded plug.
TABLE 11
Supply Line and Manifold Pressure (inches w.c.)
Unit | Fuel | Manifold | Line Pressure | |
Pressure | ||||
|
|
| ||
|
|
|
| |
|
|
|
| |
All | Nat. Gas | 3.5 | 4.5 - 10.5 | |
|
|
|
| |
All | L.P. Gas | 10.0 | 11.0 - 13.0 | |
|
|
|
|
NOTE - A natural to L.P. propane gas changeover kit is necessary to convert this unit. Refer to the changeover kit installation instruction for the conversion procedure.
Page 41
