5-565.1
25
(47) electronic modulating gas valve – (oPt)
An electronic modulating gas valve is provided factory installed
in the duct furnace gas train when the unit is equipped with
Electronic Modulating Gas Controls (Digit 12 = 4, 5, 6, 7, or 8).
The gas valve modulates the firing rate between 40% to 100%
full fire based on the input signal from the Electronic Modulation
Amplifier or Signal Conditioner. For additional information, refer
to Control Operating Sequence.
(48) air flow Proving switch – (oPt)
The air flow proving switch is factory installed in the duct furnace
electrical junction box. The air flow proving switch monitors
the pressure differential between the duct furnace and the
atmosphere. The purpose of the air flow proving switch is to cut
power to the gas controls if a positive pressure is not measured
by the switch. This could be caused by a lack of air movement
through the heat exchanger.
note: The air flow proving switch will prevent any heat
exchanger warm-up because the gas controls can not
be energized until air flow is proven.
setting the air flow Proving switch
The range of the air flow proving switch is adjustable between 0.17"
to 5.0" W.C.
1. Set the thermostat so that there is a call for heat. This should start
the blower and then the burner ignition sequence.
2. Turn the set screw of the pressure switch clockwise until it stops.
This will set the pressure at 5.0" W.C.
3. Turn the screw counter-clockwise until the gas controls light and
then one additional full turn (This is approximately 0.25'' W.C.).
This will allow for dirty filters or any other slight static pressure
increases in the system.
(49) High limit switch
Automatic – (STD)
The automatic reset high limit switch is factory installed in the
duct furnace electrical junction box. If the limit temperature is
exceeded, the gas controls are de-energized until the switch
is cooled.
Manual – (OPT)
The manual reset high limit switch is factory installed in place
of the standard automatic reset high limit switch located in the
duct furnace electrical junction box. In case of a failure of the
blower motor, blockage of the inlet air, etc., the manual reset
switch prevents the unit from cycling on the high limit. If the limit
temperature is exceeded, a service person must inspect the unit
for the cause of the high discharge temperature, take corrective
action, and then reset the switch.
(50) supply air fire stat – (oPt)
The supply air fire stat is factory installed in the duct furnace
electrical junction box with the sensor in the discharge air
stream. In case of elevated temperatures in the supply air
stream, the manual reset switch shuts down the entire unit. If
the limit temperature is exceeded, a service person must inspect
the unit for the cause of the high discharge temperature, take
corrective action, and then reset the switch.
(51) main gas valve – (std)
The main gas valve is factory installed in the duct furnace gas
train. The main gas valve provides the pilot, regulator, main gas,
and manual shutoff functions. For additional information, see the
supplier literature included with the unit.
(52) Burner Box – (std)
The burner box is located in the duct furnace section and contains
the burner and pilot assembly. The burner box includes an access
panel for removal of the burner for inspection and servicing.
(55) differential Pressure switch
A differential pressure switch is supplied on all power vented
duct furnaces and is designed to prevent operation of the main
burner in the event there is improper venting through the vent
system. This may occur due to a restricted vent, inadequate
vent draw, uninsulated vent pipe in cold ambient or long vent
runs, excessive vent diameter, restricitve vent terminal, negative
pressure within space, etc. See Troubleshooting section for
more information.
(not shown) circuit analyzer – (oPt)
The circuit analyzer is factory installed on the door of the
electrical section. The circuit analyzer is used to quickly assist
service personnel in troubleshooting by monitoring the unit firing
sequence and vital operating steps. Lights will come on as a
point of electrical operation is passed and proven. If any light is
not lit, that is the point where failure occurred.
figure 25.1 - circuit analyzer
Circuit analyzer tagging will vary based on the unit ordered.
Circuit analyzer shown is for reference only.
oPtions
