Allied A80UH1EX - Page 10

508031-02Issue 2135Page 10 of 29
Thermal Switch (Figure 6)
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. When the switch
senses excessive temperature, the circuit breaks and the
ignition control immediately stops ignition and closes the
gas valve.
Primary Limit Control
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 control will go into Watchguard 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.
Flame Sensor (Figure 6)
A ame sensor is located on the top of the air gas plenum.
The sensor can be removed for service without removing
the burner. During operation, ame is sensed by current
passed through the ame and sensing electrode. The
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 5 for ame signal.
Flame Signal in Microamps
Normal Low Drop Out
1.5 greater 0.5 - 1.4 0.4 or less
Table 5.
Gas Valve (Figure 6)
The valve 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.
Air Gas Plenum
Burner
Gasket
Gas Manifold
Gas Valve
Air Orifice
Sensor
Ignitor
Gas Orifice
Thermal
Switch
(location)
Intake Air Screen
Intake Air
Elbow
Figure 6. Heating Components