Heat Controller, Inc.
MGD-B SERIES GAS FURNACE
Owner’s Manual
G18D Series Gas Furnace
OWNER’S MANUAL
Mortex Products Inc. / Fort Worth, TX 76106
G18D Owner’s Manual
4
The igniter warm-up period is extended to 27 seconds then,
24 VAC is sent to the gas valve solenoid opening the solenoid
and star
ti
ng the
fl
ow of gas. If a
fl
ame is established for more
than 10 seconds during the retry the unit will con
ti
nue to
operate normally and the control board will clear the igni
ti
on
retry counter. If a
fl
ame has not been established then the
control board will advance the retry counter and will con
ti
nue
the igni
ti
on retry opera
ti
on. The igni
ti
on retry opera
ti
on will
a
tt
empt to re-ignite the gas burner a total of three igni
ti
on
cycles during a call for heat from the thermostat. If the
burner
fl
ame has not been established a
ft
er the third igni
ti
on
retry cycle the control board will go into a so
ft
lockout for a
period of one hour. If there is s
ti
ll a call for heat a
ft
er the one
hour lockout the furnace will ini
ti
ate a normal start cycle. If
the problem has not been corrected the furnace will lockout
again a
ft
er the three igni
ti
on retries.
Call For Heat Removed
If the call for heat from the thermostat is removed from the
control board before the board can resume normal opera
ti
on
the control board will clear the igni
ti
on retry counter, will
clear a so
ft
lockout and will clear any fault codes.
Call For Heat Removed With Gas Valve Stuck Open
If the furnace is running normally and the call for heat from
the thermostat has been removed the 24 VAC signal to the
gas valve solenoid will be removed. If the control board
so
ft
ware indicates a microamp signal is present at the
fl
ame
sensor indica
ti
ng a
fl
ame is present the control board will
keep 115 VAC present to the combus
ti
on air booster motor,
115 VAC to the heat terminal for the indoor fan to keep the
indoor fan motor energized and will
fl
ash a error code of 5
fl
ashes indica
ti
ng a
fl
ow of gas with no call for heat. The
furnace will con
ti
nue to operate at this condi
ti
on un
ti
l the
gas
fl
ow has been interrupted and the
fl
ame has been
ex
ti
nguished.
OBSERVING BURNER OPERATION
The combus
ti
on air booster motor is located inside the white
plas
ti
c assembly a
tt
ached to the 4” round galvanized pipe.
When the combus
ti
on air booster motor has been energized
the fans create a
fl
ow of air through the booster motor
assembly and the burner box that produces a nega
ti
ve
pressure at the top of the booster motor assembly and a
posi
ti
ve pressure at the burner box. A tube is a
tt
ached to the
pressure port at the top of the booster motor assembly and
the top of the burner box that extends to the pressure ports
on the pressure switch, providing the nega
ti
ve and posi
ti
ve
pressures to the switch. If the pressures applied to the
posi
ti
ve and nega
ti
ve ports (Di
ff
eren
ti
al Pressure) of the
pressure switch exceed -0.2” wc +/ .05” wc the switch
electrical contacts close providing a 24 VAC signal back to the
control board thru the blue wires a
tt
ached to the 9 pin plug
indica
ti
ng to the control board so
ft
ware the pressure switch
has closed.
When the pressure switch has closed the control board starts
a 30 second igni
ti
on warm up. This gives the hot surface
igniter 30 seconds to obtain its normal opera
ti
ng
temperature. A
ft
er the 30 second igni
ti
on warm up, the
control board sends 24 VAC to the thru the brown wires on
the 9 pin plug to the gas valve solenoid for 10 seconds which
will open the gas valve and start the
fl
ow of gas. The hot
surface igniter should ignite the
fl
ow of gas and start the
fl
ame stabiliza
ti
on period. During the
fl
ame stabiliza
ti
on
period the
fl
ame sensor will send a microamp signal of 1.5
to 3.7 microamps
(0.0000015 to
0.0000036 amps)
thru
the
yellow wire that is connected to the 9 pin plug on the control
board signaling to the control board so
ft
ware that a
fl
ame is
present. The indoor blower
ti
me delay will start a 50 second
on delay a
ft
er the
fl
ame stabiliza
ti
on period has concluded
and the control board will place 115 VAC on the HEAT
terminal of the control board energizing the indoor fan in the
hea
ti
ng mode. The furnace will con
ti
nue to operate un
ti
l the
call for heat from the thermostat has been sa
ti
s
fi
ed. At this
point the gas valve solenoid will be de-energized, the burner
fl
ame will be ex
ti
nguished and the control board so
ft
ware will
start a 50 second indoor fan o
ff
delay. When the indoor fan
has de-energized the control board will indicate a steady
green light on the diagnos
ti
c indicator indica
ti
ng the control
board is ready to resume normal opera
ti
on.
Igni
ti
on Retry
If the burner
fl
ame has not been established or has been
interrupted when the thermostat is calling for heat; the
control board will start the igni
ti
on retry opera
ti
on. During
the retry opera
ti
on the combus
ti
on air booster motor will
con
ti
nue to operate. The control will start a 15 second purge
to vent any unburned gas from the heat exchanger.
1. Observe burner to make sure it ignites and to
observe the
fl
ame color. With Natural gas, the
fl
ame will be blue with yellow
ti
ps; with Propane
gas, a yellow
fl
ame can be expected.
2. Allow furnace to heat up un
ti
l the blower cycles on.
(2-1/2 min.)
3. Turn wall thermostat down.
4. Observe main burner
fl
ame to make sure it shuts
o
ff
.
5. Let furnace cool and blower turns o
ff
.
6. If any abnormali
ti
es should occur, such as the burner
failing to light or to turn o
ff
, the
fl
ame looks sooty or
it seems to be “
fl
oa
ti
ng” around inside the heat
exchanger, call a quali
fi
ed service technician for
service.
4
