POST START CHECKLIST
After the entire control circuit has been energized and the heating section is operating, make the following checks:
1.Check for gas leaks in the unit piping as well as the sup- ply piping.
FIRE OR EXPLOSION HAZARD
Failure to follow the safety warning exactly could result in serious injury, death or property damage.
Never test for gas leaks with an open flame. use a commercially available soap solution made specifi- cally for the detection of leaks to check all connec- tions. A fire or explosion may result causing property damage, personal injury or loss of life.
2.Check for correct manifold gas pressures. (See ’CHECK- ING GAS INPUT’.)
3.Check the supply gas pressure. It must be within the lim- its shown on the rating nameplate. Supply pressure should be checked with all gas appliances in the building at full fire. At no time should the standby gas pressure exceed 13 in. or the operating pressure drop below 5.0 in for natural gas units. If gas pressure is outside these limits, contact the local gas utility or propane supplier for corrective action.
SHUT DOWN
1.Set the thermostat to the lowest temperature setting.
2.Turn “OFF” all electric power to unit.
3.Open gas heat access panel.
4.Turn gas valve clockwise to “OFF” position (See Figure 27).
MANIFOLD GAS PRESSURE ADJUSTMENT
This gas furnace has two heat stages. Therefore, the gas valve has two adjustment screws located under a plastic pro- tective cover. The second stage (100% input) adjustment screw is adjacent to the “HI” marking on the valve and the first stage (60% input) adjustment screw is located adjacent to the “LO” marking on the valve (See Figure 27).
Manifold pressure adjustment procedure.
Adjust second stage (100% input) pressure first, then adjust first stage (60% input) pressure.
1.Turn off all power to the unit.
2.Using the outlet pressure port on the gas valve, connect a manometer to monitor the manifold pressure.
3.Remove plastic cap covering HI and LO pressure adjust- ment screws.
4.Turn on power to the unit.
5.Set thermostat to call for second stage heat and start fur- nace.
6.If necessary, using a screwdriver, turn the second stage adjustment screw (adjacent to the “HI” marking on the valve) clockwise to increase manifold pressure or coun- terclockwise to decrease manifold pressure. Be sure not to
7.After the high manifold pressure has been checked, adjust the thermostat to call for first stage heat.
8.If necessary, using a screwdriver, turn the first stage adjustment screw (adjacent to the “LO” marking on the valve) clockwise to increase manifold pressure or counterclockwise to decrease manifold pressure. Be sure not to
9.Once pressure has been checked, replace the plastic cap covering the HI and LO pressure adjustment screws.
NOTE: When using natural gas, the manifold pressure for second stage (100% input) should be 3.5 IWG ±
0.3.The manifold pressure for first stage (60% input) when using natural gas should be 1.5 IWG ±
CHECKING GAS INPUT
NATURAL GAS
This unit has two stages of gas heat. The first stage is 60% of the full fire input and is considered the minimum input for the furnace. The intended input for each furnace is shown in the table below. The following Table applies to units operating on 60 Hz power only.
TABLE 26: GAS HEAT STAGES
| 2nd Stage | 1st Stage |
# of Burner Tubes | Input (100% | Input (60% |
| Btuh) | Btuh) |
|
|
|
6 | 180,000 | 108,000 |
|
|
|
8 | 240,000 | 144,000 |
|
|
|
To determine the rate of gas flow (second Stage).
1.Turn of all other gas appliances connected to the gas meter.
2.Turn on the furnace and make sure the thermostat is calling for Second stage (100% input) heat.
40 | Unitary Products Group |
