MG3P Installation Manual
27
f.) Repeat steps 8 thru 12 for replacement of the LOW fire
spring and adjustment screw.
g.) Check and adjust the regulator setting. See Gas Pressure
Adjustment Section.
h.) Reinstall the cap screws on the HIGH and LOW regulators.
Replacement cap screws are provided in the conversion
kit.
i.) Affix the label from the conversion kit to the gas valve.
13. Install the gas manifold assembly back into the burner
assembly. Make sure the center of the orifices are aligned
with center of the burners.
14. Secure the manifold assembly to the burner assembly with
the four screws, removed in step 8.
15. Reconnect the gas piping to the gas valve inlet.
16. Reconnect the wires to the gas valve terminals.
Measuring the Supply Gas Pressure
To obtain an accurate pressure reading, turn off all gas
appliances (i.e. Dryers, water heaters, stoves, etc.) at their
ON/OFF control or individual gas valves.
1. Remove the inlet pressure plug (Figure 36 (page 26)) from
the INLET side of the gas valve with a 3/16 Allen wrench.
2. Install a 1/8 NPT fitting, which is compatible with a manometer
or similar pressure gauge.
3. Connect the manometer or pressure gauge to the inlet pressure
tap.
4. Turn on all electrical power to the furnace.
5. Turn the main gas supply valve (on the outside of the unit) to
the ON position.
6. Start the furnace by adjusting the thermostat to it’s highest
setting. Allow the furnace to run for 10 minutes.
7. Check the incoming gas line pressure. Propane gas furnaces
must be between 11.0”-14.0” W.C. Natural gas installations
must be between 4.5”-10.0” W.C. If the pressure is not between
these specified ranges, contact your local gas supplier for
adjustment.
8. Adjust the thermostat to it’s lowest setting and allow the unit
to cycle off.
9. Turn the main gas supply valve (on the outside of the unit) to
the OFF position.
10. Turn off all electrical power to the furnace.
11. Disconnect the manometer or pressure gauge.
12. Remove the NPT fitting and reinstall the inlet pressure plug.
NOTE: To prevent cross threading, hand tighten the plug
first, then tighten with 3/16 Allen wrench.
Figure 37. Burner & Manifold Assembly
Wire Te rminals
Gas Valve Inlet
Screws (x4)
Manifold
Burner Assembly
Burner
Orifices
ON/OFF
Knob
Measuring the Manifold Pressure
The manifold pressure must be measured by installing a pressure
gauge (Manometer, Magnehelic Meter, etc.) to the outlet end
of the gas valve.
1. Remove the manifold pressure plug (Figure 36 (page 26))
from the outlet side of the gas valve with a 3/16 Allen wrench.
2. Install a 1/8 NPT fitting, which is compatible with a Manometer
or similar pressure gauge.
3. Connect the manometer or pressure gauge to the pipe thread
fitting.
4. Start the furnace by adjusting the thermostat 5 degrees above
room temperature. Allow the furnace to operate for 3 minutes.
5. Measure the manifold pressure on the manometer or pressure
gauge. Compare the measured value to the value in Table
19 (page 48).
6. If the manifold pressure is not set to the pressure
specified in Table 19, remove the pressure regulator cap
(Figure 36) from the gas valve. Slowly turn the adjusting
screw underneath the cap with a small screwdriver
until the appropriate manifold pressure is obtained.
NOTE: Turning the screw clockwise increases the pressure,
turning the screw counter-clockwise decreases the pressure.
7. After the manifold pressure is properly set, replace the cap
so that the letters facing up represent the type of gas being
used for the furnace. See Figure 36.
8. Adjust the thermostat to its lowest setting.
9. Turn off the main gas supply to the unit at the manual shut-off
valve, which is located outside of the unit.
10. Turn off all of the electrical power to the furnace.
11. Disconnect the manometer or pressure gauge.
12. Remove the 1/8 NPT fitting and reinstall the manifold pressure
plug. NOTE: To prevent cross threading, hand tighten the
plug first then tighten with 3/16 Allen wrench.
Completing the Conversion
1. Turn the main gas supply valve (on the outside of the furnace)
to the ON position.
WARNING:
FIRE OR EXPLOSION HAZARD
Never test for gas leaks with an open flame. Check
all connections using a commercially available
soap solution. A fire or explosion may result
causing property damage, personal injury or
loss of life. Failure to follow the safety warnings
exactly could result in serious injury, death or
property damage.
2. Check all gas connections for leaks with a soap and water
solution. If the solution bubbles there is a gas leak which must
be corrected.
3. Turn on all electrical power to the furnace.
4. Turn the gas valve ON/OFF knob (Figure 36) to the ON
position.
5. Start the furnace by adjusting the thermostat 5 degrees above
room temperature.
6. Check the furnace for proper ignition and operating sequence
(See page 32).
7. After ignition, visually inspect the burner assembly to verify
that the flame is drawn directly into the center of the heat
exchanger tube.
NOTES:
In a properly adjusted burner assembly, the flame color should
be blue with some light yellow streaks near the outer portions
of the flame.