Flame Sensor ("Cad Cell") Checkout Procedure - Trane Highboy THV1M087A936SA Service Facts

D. Symptom: Unable to achieve clean combustion by
making burner air adjustments.
Items to check:
1) Measure the burner air tube insertion depth and
alignment. The end of the tube should not protrude
inside the combustion chamber. The end of the tube
should be approximately ¼ inch away from the inner
wall surface of the combustion chamber.
2) Inspect the oil nozzle for excessive wear, blockage, or
deterioration. Measure and, if necessary, reset the nozzle
depth or turbulator location with respect to end of the
burner head. Replace the nozzle, if necessary (refer to the
oil burner manufacturer's instructions).
3) Measure the oil pump pressure. If required, adjust the
pressure to burner nameplate value. (This is the typical
minimum pressure required to obtain the full input rate
from the furnace).
4) Verify the burner is configured as specified in Table
1 and adjusted according to the Initial Burner
Operation section of this manual (page 8) and the
burner manufacturer's instructions.
5) Measure the overfire draft. If required, adjust the
barometric damper to increase the stack draft to obtain
an overfire draft of 0.02 in. W.G. with the burner operat-
ing. (This is the typical minimum draft required to
obtain the specified flue gas combustion analysis values
given in Table 1.) If the specified overfire draft cannot be
obtained with a stack draft of 0.02 in. W.G., the heat
exchanger may be partially blocked and could require
cleaning.
6) Measure the draft at the point where the vent connector
attaches to the heat exchanger flue pipe. With the burner
operating, the stack draft should not exceed 0.05 in. W.G.
If the stack draft has been adjusted above this value to
give the proper overfire draft, the heat exchanger will
require cleaning.
If there is little or no stack draft, the chimney flue way
may require cleaning, the chimney is too restrictive, or a
downdraft condition exists.
E. Symptom: Furnace blower will not start.
Items to check:
1) Confirm there is 120 VAC at the blower motor terminal
block.
2) If there is not 120 VAC at the blower terminal block,
measure the voltage at the fan center relay. If the fan can
be activated by itself from the room Comfort Control
subbase, confirm it will operate.
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OFF-SF-1B
Service Facts
If so, the fan center relay contacts may be burnt, or
damaged, or the fan limit control may be defective. Test
these components and replace the defective component,
as required.
3) If there is 120 VAC at the blower terminal block, either
the run capacitor or blower motor may be damaged. Test
and replace the capacitor or motor, as required.
F. Symptom: Blower cycles on and off after the burner
has shutdown.
Item to check:
1) Increase the fan limit control differential. Typically, the
fan "off" setting should be 30 degrees F. below the fan
"on" setting. Adjust the setting as required.
▲
WARNING
!
FIRE HAZARD
If the fan and high limit control is faulty, it should be re-
placed. However, it must only be replaced by the same
make and model as the original. All the original temperature
settings should be duplicated on the replacement model as
well. REMOVE THE LOW VOLTAGE JUMPER IN THE CON-
TROL, IF EQUIPPED. See Figure 1. Refer to the electrical
diagram for proper electrical connections. (page 10 & 11)
FLAME SENSOR ("CAD CELL") CHECKOUT
PROCEDURE
On the Honeywell oil primary control, to check the electrical
resistance of the flame sensor (referred to as a cadmium
sulfide photocell, or "cad cell"), depress the reset button on
the oil primary safety control while the burner is firing. The
oil primary control will report the measured resistance range
of the cad cell by flashing the LED (light emitting diode) one
(1) to four (4) times. Refer to the oil burner manufacturer's
instructions for further details.
For all primary controls, an alternate procedure to check the
flame sensor operation is as follows:
1) Remove the flame sensor lead wires from the terminals
(labeled "CAD CELL" on the underside of the Honeywell
control) of the oil primary safety control module. Start
the burner. Shortly after combustion is established,
place a temporary jumper wire across the cad cell
terminals, or leads, of the control. Connect an ohmmeter
across the flame sensor lead wires. The measured
resistance should be less than,
- 1600 Ohms for the Honeywell cad cell.
2) Stop the burner and remove the jumper wire.
3) With the burner off, measure the resistance of the flame
sensor with the ohmmeter. The resistance of the sensor
without "seeing" a light source (so-called "dark" cell
resistance) should be greater than,
- 20,000 Ohms for the Honeywell cad cell.
4) If the sensor resistances are outside the acceptable
ranges given above, confirm the lens of the cell is clean
and the cell is located correctly in the burner housing. If
the cell is clean and correctly located, replace the flame
sensor.
NOTICE: All resistances are approximate values only and
will vary depending upon the intensity of the light source
(flame or sunlight) and the condition or age of the cad cell.
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