59MN7C: Installation, Start-up, Operating and Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
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2. Loosen set screw on inlet tower pressure tap no more than one full
turn with a 3/32-in. hex wrench or remove the 1/8 in. NPT plug
from the inlet pressure tap on the gas valve.
3. Connect a manometer to the inlet pressure tap on gas valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper the R to W/W1 and W2 thermostat connections at the
furnace control board.
8. When main burners ignite, confirm inlet gas pressure is Between
4.5 in. w.c. and 13.6 in. w.c.
9. Remove jumper across thermostat connections to terminate call for
heat. Wait until the blower off delay is completed.
10. Turn furnace gas valve electric switch to OFF position.
11. Turn gas supply manual shutoff valve to OFF position.
12. Turn off furnace power supply.
13. Remove manometer from the inlet pressure tap of the gas valve.
14. Tighten set screw on inlet tower pressure tap with 3/32-in. hex
wrench, or if 1/8-in. NPT plug was removed, apply pipe dope
sparingly to end of plug and re-install in the gas valve.
Adjust Manifold Pressure - Maximum Heat
For proper operation and long term reliability, the manifold pressure
must be adjusted within +/-2 percent of input rate on furnace rating plate.
The modulating furnace manifold pressure is set at two points. The first
point is Maximum Heat. The second point is Minimum Heat. Do not
adjust Intermediate Heat manifold pressure. Intermediate Heat manifold
pressure is checked as part of the temperature rise, but is not adjustable.
Always adjust Maximum Heat first, then Minimum Heat.
To adjust manifold pressure to obtain input rate for Maximum Heat:
1. Make sure the gas supply is turned off to the furnace and at the
electric switch on the gas valve.
2. Loosen set screw on manifold tower pressure tap no more than one
full turn with a 3/32-in. hex wrench, or remove the 1/8 in. NPT plug
from the manifold pressure tap on the gas valve, see Fig. 63.
A170116
Fig. 63 – Gas Valve with Tower Pressure Ports
3. Connect a manometer to the outlet pressure tap on gas valve.
4. Turn on furnace power supply.
5. Turn gas supply manual shutoff valve to ON position.
6. Turn furnace gas valve switch to ON position.
7. Jumper the R to W/W1 and W2 thermostat connections at the
furnace control board.
8. After the main burners ignite and the blower starts, confirm
Maximum Heat manifold pressure is correct, based on the manifold
pressure tables in the installation instructions.
9. To adjust the Maximum Heat manifold pressure, slowly turn
adjusting screw counterclockwise to decrease manifold pressure or
clockwise to increase manifold pressure. Turn adjustment no more
than one click per second until you obtain the required manifold
pressure, see Fig. 64.
A10496
Fig. 64 – Gas Valve without Tower Pressure Ports
10. Main burner flame should be clear blue, almost transparent.
11. After adjusting the Maximum Heat manifold pressure, remove
jumpers across thermostat connections to terminate the call for
heat.
12. Wait for blower off-delay to finish then reset 115-V power to
furnace.
Adjust Manifold Pressure - Minimum Heat
To adjust manifold pressure to obtain input rate for Minimum Heat:
1. On the 3 digit display, navigate to (Htt) and select (2St-lHt). This
keeps furnace locked in low-heat operation when only W/W1 is
energized.
2. Jumper R and W/W1 thermostat connections on control to start
furnace.
WARNING
!
FIRE HAZARD
Failure to follow this warning could result in personal injury, death,
and/or property damage.
Inlet pressure tap set screw must be tightened and ⅛-in. NPT pipe plug
must be installed to prevent gas leaks.
NOTICE
!
DO NOT set Maximum Heat manifold pressure less than 3.2-in. w.c. or
more than 3.8 in. w.c. for natural gas. If required manifold pressure is
outside this range, change main burner orifices to obtain manifold
pressure in this range.
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