SERVICING
23
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CHECKING PRESSURE TRANSDUCER (96% ULN)
The 96% ULN products utilize a pressure transducer. The
pressure transducer signals the control board to modulate the
heating cycle during a call for heat by regulating the induced
draft motor speed. By regulating the speed of the induced
draft motor, proper air-fuel ratios are maintained.
Sensing range specification: 0.0-2.0 inches W.C.
Voltage specifications:
• Steady State: 5.0 vDC from red to green wire (transducer
wiring harness input)
• With Inducer off: 0.25 vDC from black to green wire
(transducer wiring harness output).
• During operation: Output range equals 0.25 - 4.0 vDC
Potential errors:
1. Control board does not receive 0.25 vDC for inducer motor
with motor off
a. Will result in 2-flash error code on the control board
2. Control board does not receive the required voltage
change (0.25 - 4.0 vDC) during inducer motor operation.
a. Will result in 3-flash error code on the control board
CHECKING FOR DELAYED IGNITION
Delayed ignition is a delay in lighting a combustible mixture
of gas and air which has accumulated in the combustion
chamber.
Furnace design makes this extremely unlikely unless safety
controls have been by-passed or tampered with. Never by-
pass or alter furnace controls.
If delayed ignition should occur, the following should be
checked:
1. Improper gas pressure - adjust to proper pressure (See
CHECKING GAS PRESSURE
).
FIELD TEST MODE
Function: When the SW1 button is pressed and held until
the LED is blinking in AMBER (more than 10 seconds, less
than 15 seconds), the control will execute a field test mode
sequence to cycle through component operation.
Operation: The control must be powered and the thermostat
satisfied (no call for heat or cool). Depress and hold the SW1
button for at least 10 seconds (but not more than 15 seconds),
until the LED is blinking in AMBER, then release. The control
will execute the following functions:
1. Blower - “Heat” Speed 15 seconds
2. Blower - “Cool” Speed 15 seconds
3. Blower - “Fan” Speed 15 seconds
4. Hot Surface Igniter 17 seconds
5. Inducer - “Run” setting 15 seconds
6. Inducer - 1.0” w.c. 60 seconds
7. Return to OFF mode
Once the Field Test Mode is initiated, all thermostat inputs
will be ignored until the field test sequence is completed. If
the SW1 button is held for more than 15 seconds, the button
press will be ignored and the LED display will return to its
prior state.
CHECKING INTEGRATED IGNITION CONTROL
BOARDS
NOTE:
Failure to earth ground the furnace, reversing the
neutral and hot wire connection to the line (polarity), or a
high resistance connection in the neutral line may cause the
control to lockout due to failure to sense flame.
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WARNING
The ground wire must run from the furnace all the way back
to the electrical panel. Proper grounding can be confirmed by
disconnecting the electrical power and measuring resistance
between the neutral (white) connection and the burner closest
to the flame sensor. Resistance should be less than 10 ohms.
The ignition control is a combination electronic and
electromechanical device and is not field repairable. Complete
unit must be replaced.
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These tests must be completed within a given time frame due
to the operation of the ignition control.
1. Check for 120 volts from Line 1 (Hot) to Line 2 (Neutral)
at the ignition control. No voltage, check the door switch
connections and wire harness for continuity.
2. Check for 24 volts from W to C terminal on the ignition
control. No voltage. Check transformer, room thermostat,
and wiring.
If you have 24 volts coming off the transformer but receive
approximately 13 volts on the terminal board between (C)
and (R), check for blown fuse.
3. Check for 120 volts to the induced draft blower by
Summary of Contents for AMES960403BU AA
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