5-565.1
16
start-uP Procedure
single-stage gas controls (intermittent pilot)
Utilizes a single-stage combination gas control, an ignition
control, and a single-stage low voltage thermostat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes. The power exhauster
relay pre-purge timer closes after 20 to 40 seconds
energizing the gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The unit continues to operate until the thermostat is
satisfied, at which time both the main and pilot valves close
100%. (If the unit was not provided with a time delay relay,
the blower stops at this time).
8. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
two-stage gas controls (intermittent pilot)
Utilizes a two-stage combination gas control, an ignition control,
and a two-stage low voltage thermostat. The unit fires at 50%
fire on low stage and 100% fire on high stage.
1. The thermostat calls for low stage heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes. The power exhauster
relay pre-purge timer closes after 20 to 40 seconds
energizing the gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
50% fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. If the temperature at the thermostat continues to fall, the
thermostat will call for high stage heat.
8. The main gas valve is opened completely and the main
burner is lit to 100% full fire.
9. The unit continues to operate until the high stage of the
thermostat is satisfied, at which time the main valve closes
to 50% fire.
10. The unit continues to operate until the low stage thermostat
is satisfied, at which time both the main and pilot valves
close 100%. (If the unit was not provided with a time delay
relay, the blower stops at this time.)
11. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
mechanical modulating gas controls
dial number
lo
1
2
3
4
5
6
7
8
Hi
discharge
air temp. 58
62
65
69
72 76
79
83
86 90
(°f)
modulating gas valve in one of ten positions. A hydrostatic
sensing bulb located in the discharge air stream controls the gas
flow between 40% through 100% full fire. When the discharge
air hydrostatic sensing bulb is satisfied, the modulating valve
closes completely, but the pilot remains lit. This control cannot
be used with a room override thermostat.
1. Power is supplied to the unit through either an exhaust fan
interlock contact or a start/stop switch.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes. The power exhauster
relay pre-purge timer closes after 20 to 40 seconds
energizing the gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The hydrostatic sensing bulb, integral to the mechanical
modulating gas valve, calls for heat. The main gas valve is
opened and the main burner is lit. The burner modulates
between 40% through 100% fire based on the call for heat.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The unit continues to operate until the hydrostatic sensing
bulb is satisfied, at which time the main valve closes 100%,
but the pilot remains lit.
8. The unit blower (and pilot) continues to operate until either
an exhaust fan interlock contact or a start/stop switch is
opened. If the unit was provided with a time delay relay, the
blower stops after 30 to 45 seconds.
electronic modulating gas controls
single furnace - model sizes 75-400
Utilizes an electronic modulating/regulating gas control,
combination gas valve, an ignition control, modulating amplifier,
and either a modulating room thermostat or modulating duct
thermostat with remote temperature set point adjuster. The
thermostat controls can modulate the gas flow between 40%
through 100% full fire. When the thermostat is satisfied, the amplifier
cuts power to the combination gas valve which prevents gas
flow to both the main and pilot burners.
When duct sensing is utilized, a room override thermostat can
be added. When calling for heat, the room override thermostat
provides full fire operation until the space temperature is
satisfied. Control is then returned to the duct sensing control.
In this situation, either the duct sensor or the room override
thermostat can call for heat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed,
the differential pressure switch closes. The power exhauster
relay pre-purge timer closes after 20 to 40 seconds
energizing the gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The modulating gas valve can be controlled by either an
electronic modulating room or duct thermostat. The thermostat
can modulate the firing rate between 40% through 100% full
fire. The call for heat is created by a resistance signal (8000
to 12000 ohms) in the thermostat. The amplifier converts this
resistance into a DC voltage (0 to 12 volts DC with 0 volts
high fire and 12 volts low fire). The output voltage is applied
to the modulating gas valve to control the gas flow to the
Utilizes a mechanical modulating gas control and an ignition
control. The mechanical modulating gas control is designed
for use in constant blower applications. The discharge air
temperature is maintained by setting the control dial of the
