Allied A97UH2E - Page 23

508433-01 Issue 2345 Page 23 of 70
Heating Components
Ignitor
The ignitor is made of durable silicon nitride. The integrated
control provides 120 volts to the ignitor for a consistent
ignition and long ignitor life. Ohm value should be 39 to 70.
See Figure 12 for ignitor location and Figure 13 for ignitor
check out.
NOTE: The A97UH2E 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 left side of the burner
support. See Figure 12. The sensor tip protrudes into the
ame envelope of the left-most burner. The sensor can
be removed for service without removing any part of the
burners. 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 8 for ame signal.
Normal Low Drop Out
2.6 or greater 2.5 or less 0.6
Table 8. Flame Signal in Microamps
Gas Valve
The valve (Figure 12) 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.
LPG change over kits are available from Allied. Kits include
burner orices and a gas valve.
Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on
top of the burner box, one on each side.- See Figure 12.
The limit is a N.C. SPST manual-reset limit. When S47
senses rollout, the circuit breaks and the ignition control
immediately stops ignition and closes the gas valve.
Rollout can be caused by a blocked exchanger, ue or lack
of combustion air. The switch is factory set to trip (open) at
210°F and cannot be adjusted. The switch can be manually
reset. To manually reset a tripped switch, push the reset
button located on the control.
Burners
All units use inshot burners. Burners are factory set and
require no adjustment. Always operate the unit with the
burner box front panel in place. Each burner uses an orice
that is precisely matched to the burner input. Burners can
be removed as a one piece assembly for service. If burner
assembly has been removed, it is critical to align center
of each burner to the center of the clamshell when re-
installing. See more detail in Section VI- MAINTENANCE.
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 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. When removing switch make note of
orientation. When replacing switch make sure the three
mounting holes are lined up with the screw holes in the
vestibule for correct orientation.
Figure 11. Primary Limit Control (S10)
Mounting Hole
Mounting Hole
Mounting Hole