Oil Furnace Sequence Of Operation; Typical Primary Control Sequence Of Operation - York International DFAA User's Information, Maintenance And Service Manual

107273-UUM-C-0306
To Replace Blower Wheel:
1. Turn off all power to the burner before servicing.
2. Disconnect the burner motor wires.
3. Remove the bolts securing the blower motor to the
housing.
4. Remove the blower motor and wheel.
5. Remove the existing wheel.
6. As shown at right, slide the new blower wheel onto the shaft.
• Slide blower wheel toward motor until the bottom rim is 1/8" from
the motor face.
• Rotate the wheel until the set screw is centered on the flat of the
motor shaft.
• Tighten the set screw to secure the wheel.
7. Install the motor on the burner housing. Tighten the bolts. Recon-
nect the motor wires.
8. Restore power, start the burner, and perform combustion tests.
Refer to "Set combustion with instruments."
Check / Adjust Electrodes
Check the electrode tip settings. Adjust if necessary to comply with the
dimensions shown in Figure 10. To adjust, loosen the electrode clamp
screw and slide / rotate the electrodes as necessary. Securely tighten
the clamp screw when finished.
END VIEW
5/32"
Gap
5/16" above
nozzle center
FIGURE 10: Electrode Settings
U
Label all wires prior to disconnection when servicing controls.
Wiring errors can cause improper and dangerous operation.
Verify proper operation after servicing.

OIL FURNACE SEQUENCE OF OPERATION

The following describes the sequence of operation of the furnace. Refer
to Figure 1 for component location.
Continuous Blower
DFAA cooling/heating thermostats have a fan switch that has an ON
and AUTO position. In the ON position the thermostat circuit is com-
pleted between terminals R and G. The motor will operate continuously.
DFAH models are heating only.
Intermittent Blower - Cooling
Cooling/heating thermostats have a fan switch that has an ON and
AUTO position. In the AUTO position the thermostat circuit is completed
between terminals R and G when there is a call for cooling. The motor
will operate until the call for cooling is removed by the thermostat.
8
SIDE VIEW
Nozzle-to-tip
1/16"
Spacing
Heating Cycle
When the thermostat switch on a DFAA is set on HEAT and the fan is
set on AUTO, (DFAH has no manual fan operation), and there is a call
for heat, a circuit is completed between terminals R and W of the ther-
mostat. There is a 10 second delay to allow the burner motor to come
up to speed at which time the primary control provides power to the igni-
tion transformer, the solenoid valve on the oil pump opens and fuel oil
starts to flow to the nozzle, ignition occurs and the flame sensor begins
its sensing function. The blower motor will energize after the air temper-
ature at the fan control is above 110° F, if a flame is detected. Normal
furnace operation will continue until the thermostat circuit between R
and W is opened, which causes the ignition system and oil pump sole-
noid valve to de-energize and the burner flames to be extinguished.
The blower motor will operate until the fan switch is below 90° F. The
heating cycle is complete and ready for the start of the next cycle.
If the flame is not detected within 15 seconds of the primary control, it
will turn off the oil burner. There will be 3 retries before the primary con-
trol will lockout. If the flame is lost for 2 seconds during the 15 second
stabilization period, the ignition transformer is energized and a retry
operation begins. If flame is not detected within 15 seconds during the
retry, the primary control will go into recycle mode. Once the primary
control locks out the reset button must be pressed before an ignition
retry occurs.
A momentary loss of fuel oil, flame blowout, or a faulty cad-cell detector
will result in a disruption in the flame and be sensed within 1.0 seconds.
The oil pump solenoid valve will de-energize and the primary control will
begin a recycle operation. A normal ignition sequence will begin after a
15 second inter-purge. If during the three recycles the fuel oil supply
does not return, or the fault condition is not corrected the primary con-
trol will lock out.
During burner operation, a momentary loss of power for 50 milliseconds
or longer will de-energize the primary control. When the power is
restored, the primary control will remain de-energized and the ignition
sequence will immediately restart.
TYPICAL PRIMARY CONTROL SEQUENCE OF
OPERATION
1. STANDBY - The burner is idle, waiting for a call for heat. When a
call for heat is initiated, there is a 2-6 second delay while the con-
trol performs a safe start check.
2. VALVE-ON DELAY - If applicable, the ignition and motor are
turned on for a 15 second valve-on delay.
3. TRAIL FOR IGNITION (TFI) - The fuel valve is opened, if applica-
ble. A flame should be established within the 15 second lockout
time (30 seconds on some models).
4. LOCKOUT - If flame is not seen at the end of the TFI or is seen
during valve-on delay or postpurge, the control shuts down on
safety lockout and must be reset. If the control locks out three
times in a row, the control enters restricted lockout. Follow the
instructions on the front to reset it.
5. IGNITION CARRYOVER - Once flame is established, the ignition
remains on for an additional 10 seconds to ensure flame stability. If
the control is wired for intermittent duty ignition, the ignition unit
stays on the entire time the motor is running.
6. RUN - The burner runs until the call for heat is satisfied. The signal
is then sent to burner motor-off delay, if applicable, and it is shut
down and sent to standby.
7. RECYCLE - If the flame is lost while the burner is firing, the control
shuts down the burner, enters a 60 second recycle delay, and then
repeats the above ignition sequence. If flame is lost three times in
a row, the control locks out to prevent cycling with repetitious flame
loss due to poor combustion.
Unitary Products Group