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the cad cell is operational, replace the primary
control.
4. If the LED continues to fl ash at the interval
listed above, verify that the control is not in
restricted mode. If in restricted mode, reset it.
If not in restricted mode, replace the control.
5. If the (LED indicator for R7184 control; green
LED for 7505 control) stays off while the fl ame
is on, check the cad cell sighting for view of
the fl ame.
6. If the burner locks out, check the cad cell
resistance. (See Table 8)
7. If the burner stays running, the system is
operational.
8. If the (LED indicator for R7184 control; green
LED for 7505 control) is off, check the cad cell
assembly after disconnecting the line voltage.
Burner will not start and the LED indicator is
fl ashing at 2 seconds on, 2 seconds off for
R7184 (or the green LED is fl ashing for 7505).
• Hold the reset button down for 1 - 2 seconds.
If LED indicator continues to fl ash, wait for
60 - 70 seconds. If it still continues to fl ash,
replace the primary control.
• Honeywell R7184 control: To check cad cell
resistance, press and release the button during
the run mode, with the igniter off. The LED will
fl ash to indicate the cad cell resistance. For
proper burner operation, it is important that
the cad cell resistance is under 1600 Ohms.
For cad cell resistance, see Table 8.
• Beckett 7505 control: To check cad cell
resistance, unplug the cad cell leads (yellow
wires) from the control. Measure the resistance
with a meter in the conventional way (when a
fl ame is present). For proper burner operation,
it is important that the cad cell resistance is
under 1,600 Ohms.
Table 8. Cad Cell Resistance when
sensing fl ame
LED Flashes (Ohms) Cad Cell Resistance
1 0-400
2 400-800
3 800-1600
4 >1600
OPTIONAL ACCESSORIES
Necessary when the Furnace is Used with
Some Central Air Conditioners
If an air conditioner is installed that does not use
the furnace blower for air distribution and operates
independently of the furnace, the thermostat
system must have an interlock to prevent the
furnace and air conditioner from operating at
the same time. This interlock system usually
contains either a “Heat-Cool” switch which must
be turned to one of the positions to activate heat
or cool operation, or a positive “OFF” switch on
the cooling thermostat.
The furnace must also be equipped with an
automatic damper to prevent cold air from
being discharged up around the heat exchanger
(NORDYNE p/n 901996 for furnaces without coil
cavity, or p/n 901083 with coil cavity). See Figure
36 or 37. Cold air may cause condensation inside
the heat exchanger which can rust and lead to
early failure.
Figure 36. Coil Cavity Damper
Figure 37. Damper without Coil Cavity