18
Low Voltage Wiring – Install the thermostat per the
manufacturer's instructions. The low voltage (24 vac) connec-
tions from the thermostat are made at the terminal strip on the
control board in the furnace. See Figure 4 for the proper
connections for heating only (two-wire) and heating/cooling
(four-wire) applications. The recommended minimum wire
gauge for thermostat wiring is shown in Table 4.
The thermostat must not be installed on an outside wall or any
other location where its operation may be adversely affected.
Adverse effects include radiant loading from fireplaces, sun-
light, or lighting fixtures, and convective loading from warm air
registers or electrical appliances.
To check the heat anticipator setting:
Jump out R to W at thermostat with 10 Loop Helex and
measure current draw after blower starts. Divide by 10.
Example: 4 Amps = .4 set at .4.
OR
Set the heat anticipator according to the manufacturer's
recommendations.
Limit Control (Picture 5) – This furnace is protected by two
high temperature safety limit switches. The auxiliary (upper)
limit switch and the high temperature (lower) limit switch are
automatic reset types. If either limit trips, the burner will shut
off. Check temperature rise and compare to specifications
(45° to 75° F)
Combustion Air Relay – The combustion air relay is used
only on the M1G 077-090. On a call for heat, the relay
activates the combustion air motor. The relay is energized
through the thermostat from the “W” terminal. It has a 24VAC
coil powered by the “W” and Common terminals 3 and 1.
Terminals 4 and 2 are normally open contacts.
Combustion Air Blower – The M1G 077-090 model uses a
combustion air blower incorporated in series with the air inlet
pipe. Its purpose is to supply a forced draft method of
combustion air. The quantity of air is determined by the inlet
orifice ring, located on the inlet to the motor assembly.
Upon a call for heat under normal conditions, the combustion
blower starts up and supplies combustion air to the chamber.
If motor does not start, check to be sure call for heat is
established. See troubleshooting flow chart and sequence of
operation for further details. Then disconnect blower molex
plug and check for voltage at plug. If voltage is available and
motor does not start replace motor. If power is not available
check back through power source and combustion blower
relay contacts. See wiring diagram.
Combustion Motor Assembly Replacement
If, using the information from above, you have determined the
combustion motor assembly needs to be replaced,use the
following procedure:
1.
Disconnect Molex plug and pressure switch hoses.
2.
Remove screws from the top and break silicone loose
from orifice ring on top side of ventor assembly. (See
Figure 15). Inlet pipe may also break loose, this is normal.
3.
Remove screws from bottom of assembly and remove
the whole assembly.
4.
Mount new assembly, reattach screws removed in step 3
to bottom. Silicone around bottom, either before or after
installation of combustion air blower.
5.
Re-silicone orifice ring and combustion air pipe and
reinstall screws removed in step 2 to top.
6.
Reconnect Molex plug and pressure switch hoses from
step 1 and test.
Pressure Switch – The M1G 077-090 uses a differential type
pressure switch. The purpose of this switch is to insure that
a good supply of combustion air is supplied to the burner. The
combustion blower creates a differential in negative pressure
(less than atmospheric pressure) across the orifice ring. The
switch is normally open and closes on a drop in pressure, read
in negative inches of water column.
Picture 5. Fan and Limit Switch
Limit
Switch
Fan
Switch
Figure 15. Combustion Air Blower
Orifice
Ring
Silicone
