Allied A80US2VX - Thermal Switch; Heating Components

508033-02Issue 2135Page 24 of 48
Heating Components
Ignitor
The SureLight
®
ignitor is made of durable silicon nitride.
Ignitor longevity is enhanced by controlling voltage to the
ignitor. The integrated control provides a regulated 120
volts to the ignitor for a consistent ignition and long ignitor
life. Ohm value should be 39 to 70. See Figure 13 for ignitor
location and Figure 14 for ignitor check out.
NOTE: The A80US2VX furnace contains electronic
components that are polarity sensitive. Make sure that the
furnace is wired correctly and is properly grounded.
Flame Sensor
A ame sensor is located on the top of the air gas plenum.
See Figure 13. The sensor can be removed for service
without removing the the burner. During operation, ame is
sensed by current passed through the ame and sensing
electrode. The SureLight
®
control allows the gas valve to
remain open as long as ame signal is sensed. To check
ame sense signal use the push-button found on the
integrated control and go to Field Test Mode. The menu
will display the ame signal. See Table 15 for ame signal.
Normal Low Drop Out
2.6 or greater 2.5 or less 1.1
Table 15. Flame Signal in Microamps
Gas Valve
The valve (Figure 16) is internally redundant to assure
safety shut-o󰀨. If the gas valve must be replaced, the same
type valve must be used.
24VAC terminals and gas control knob are located on the
valve. A wire harness connects the terminals from the gas
valve to the electronic ignition control. 24V applied to the
terminals energizes the valve. Inlet and outlet pressure
taps are located on the valve. A regulator adjustment screw
is located on the valve.
Thermal Switch
The auto-reset switch is located on the front of the intake
air elbow. The switch will safely shut the unit down if
excessive temperatures are detected. See Figure 13.
When the switch senses excessive temperature, the circuit
breaks and the ignition control immediately stops ignition
and closes the gas valve.
Burner and Orice
Burners are factory set and require no adjustment. Always
operate the unit with air gas plenum in place. The burner
has one orice located between the gas valve and the
air intake assembly (Figure 13). To check or replace the
orice remove the intake air screen, coupling and intake
air elbow.Using a 5/8” socket, go through the elbow and
unscrew the gas orice. The burner uses an orice (see
Table 16) that is precisely matched to the burner input.
The burner can be removed for service. If burner has been
removed, it is critical to replace all gaskets.
Unit Input Orice Size (0 - 4500 ft)
060 0.0595
080 0.0689
100 0.0810
Table 16. Gas Orices
Primary Limit Control (S10)
The primary limit (S10) is located in the heating vestibule
panel. When excess heat is sensed in the heat exchanger,
the limit will open. If the limit is open, the furnace control
energizes the supply air blower and closes the gas valve.
The limit automatically resets when unit temperature
returns to normal. The switch must reset within three
minutes or the SureLight
®
control will go into Watch guard
for one hour. The switch is factory set and cannot be
adjusted. The switch may have a di󰀨erent set point for
each unit model number