FLAME RECTIFICATION CIRCUIT FLAME-PROVING SIGNAL MEASUREMENT PROCEDURE

StepExpected Result/Action
4. Shut off power to the unit. At the main burner enclosure, locate the wire
connected to the flame sensor electrode (FSE). Refer to the unit wiring and
parts location diagrams.
Power to unit is turned off and wire connected to the flame sensing electrode is
located.
5. Set up a microammeter to measure DC current on the lowest microamp
range. Note that the current level expected can be between 0.5 to 4.5
microamperes.
Disconnect the lead from the flame sensor electrode, then connect the
microammeter in series with the flame sensor electrode and the wire
disconnected from the electrode as shown in Figure SP-11-5.
Microammeter connected in series with flame sensor electrode output and flameproving
circuit wire in preparation for measurement.
6. Turn on power to the unit and adjust the thermostat to call for heat. After the
unit has run for about 1 minute, observe the current indication on the
microammeter and compare it to the manufacturer's specifications.
The microammeter indicates a minimum DC current of 0.5 microamperes or a
value stated in the manufacturer's specifications. This indicates that a good
flame-proving signal is being generated.
If a flame-proving signal is low or not being generated, check for the following
conditions:
• Check flame sensor rod position.
• Make sure the furnace is properly grounded per the manufacturer's
instructions. -----
• Make sure that the gas valve is grounded through the gas valve ground wire.
• Make sure that a good electrical contact exists at the flame sensor electrode
connection. ____
• Check flame sensor electrode for an oxide film coating. Clean with fine
abrasive.
If a flame-proving signal is not being generated and none of the conditions listed
above are the cause of the problem, refer to the manufacturer's instructions for
information about the operating sequence of events in the furnace and related
troubleshooting information.

pic1 7 FLAME RECTIFICATION CIRCUIT FLAME PROVING SIGNAL MEASUREMENT PROCEDURE

15. May 2019 by matt
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THERMOCOUPLE VOLTAGE MEASUREMENT PROCEDURE

StepExpected Result/Action
1, Shut off power and gas to unit.
If testing the thermocouple under no-load conditions, disconnect the
thermocouple from the gas valve by unscrewing the fitting.
If testing the thermocouple under load conditions, disconnect the
thermocouple from the gas valve by unscrewing the fitting. Screw the
thermocouple test adapter into the gas valve, then screw the thermocouple
into the adapter.
Power and gas to unit is turned off and thermocouple is disconnected from gas
valve (no-load testing) or connected to the test adapter (loaded testing).
2. Set up the VOM/DMM to measure DC voltage on a millivolt range. Note that
the voltage level expected can be 18 millivolts or higher.
If testing the thermocouple under no-load conditions, connect the one VOM/
DMM meter lead to the end contact (center) of the thermocouple and the
other meter lead to the thermocouple copper tubing as shown in Figure
SP-11-4, View A.
If testing the thermocouple under load conditions, connect one VOM/DMM
meter lead to the test adapter and the other meter lead to the thermocouple
copper tubing as shown in Figure SP-11 -4, View B.
Thermocouple and VOM/DMM prepared for measurement.
3. Turn on gas, then turn gas valve control to the pilot position. While holding
down the gas valve knob/reset button, light the pilot.
Continue to hold down the gas valve knob/reset button while observing the
VOM/DMM reading. As the thermocouple is heated by the pilot flame, the
VOM/DMM reading should begin increasing.
Continue holding down the gas valve knob or reset button for 5 minutes.
After 5 minutes, if VOM/DMM reads at least 18 millivolts (no-load test) or 9
millivolts (loaded test), this indicates the thermocouple is probably good.
If VOM/DMM reads less than 18 millivolts or 9 millivolts, check for one or more
of the following conditions:
• Yellow pilot flame • Pilot flame too small
• Pilot flame misdirected • Pilot flame flickering
• Pilot flame floating • Pilot flame lifting
• Thermocouple bent • Thermocouple lead kinked
• Thermocouple insulator damaged • Thermocouple end contact dirty
If VOM/DMM reads less than 18 millivolts or 9 millivolts, correct the problem
(listed above), or replace the thermocouple.

pic1 6 THERMOCOUPLE VOLTAGE MEASUREMENT PROCEDURE

15. May 2019 by matt
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Flame Rectification Sensor

The flame rectification sensor is commonly used in high efficiency furnaces that use direct burner ignition.

Direct Burner Ignition System Flame Rectification Circuit — Direct burner ignition systems light the burners using a hot surface ignition (HSI) or direct spark ignition method. In direct burner ignition systems, the flame sensing electrode (FSE), also called a flame rod, is used to detect that the main burner flame is established across the entire length o f the burners. When the flame rod is encircled by the burner flame, the hot gas-ionized particles conduct electricity, thus completing a circuit through the flame rod to the furnace control or ignition module. Current flow through this circuit applies a flameproving signal to the furnace control circuit microprocessor, signaling the microprocessor to keep the gas valve energized.

Flame sensing electrode operation (Figure SP-11-3) can be tested by measuring the flame-proving current signal applied to the microprocessor. This can be done by connecting an accurate ammeter capable of measuring microamps in series with the sensor input to the microprocessor. With this furnace, the ammeter should indicate a current of at least 0.5 microamps DC. Other furnaces may require a higher or lower flame sensing current. If the flame sensing current is low or nonexistent, check the following:
• Flame sensor rod position.
® The furnace is properly grounded per the manufacturer’s instructions.
• The gas valve is grounded through the gas valve ground wire.
• There is good electrical contact at the sensor connection.
• There is no oxide film coating the flame sensing electrode.
If there is a coating, clean it off by lightly rubbing with fine abrasive and wiping clean.

pic1 5 Flame Rectification Sensor

14. May 2019 by matt
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Thermocouple

Thermocouples are used on residential gas furnaces equipped with standing pilots. A standing pilot is one which burns continuously, whether the main burner is on or off. A thermocouple standing pilot is only used with a 100% shutoff main gas valve. This type of gas valve shuts off gas to the pilot and will not open its main valve if there is insufficient pilot flame to ignite the main burners or if the thermocouple is defective.

The thermocouple (Figure SP -1 1-1) is a safety control device that senses the presence of the pilot flame by generating a small DC voltage (about 30 millivolts) when subjected to the heat of the pilot flame.

pic1 3 Thermocouple

When the pilot is lit, the thermocouple develops the electrical signal that causes a small current to flow through the solenoid in the gas valve, energizing the solenoid. The energized solenoid holds the safety gas valve open, allowing gas to flow through the main gas valve to the pilot.

If the pilot flame goes out, the thermocouple cools and the voltage generated drops to zero. The current stops flowing in the solenoid, causing the safety valve to close, shutting off gas flow to the pilot and main gas valve. If the problem is suspected to be the thermocouple, visually check the pilot flame and the thermocouple for the conditions listed below before testing or replacing the thermocouple. Check for:
• Yellow pilot flame
• Pilot flame too small
• Pilot flame misdirected
• Pilot flame too low
• Pilot flame flickering
• Pilot flame floating
• Pilot flame lifting
• Thermocouple bent
• Thermocouple lead kinked
• Thermocouple insulator damaged
• Thermocouple end contact dirty

The thermocouple can be tested either under load or no-load conditions using a VOM/DMM. The procedure for both methods is provided in the detailed procedure given at the end of this section and is briefly described here.

To test the thermocouple under loaded conditions requires the use of a test adapter that allows voltage readings to be made while the thermocouple is connected to the gas valve. First, disconnect the thermocouple from the gas valve. Screw the thermocouple test adapter into the gas valve, then screw the thermocouple into the adapter (Figure SP-11-2). Connect a VOM/DMM set up on the lowest DC millivolt range to the adapter and thermocouple. Connect one meter lead to the adapter and the other lead to the thermocouple copper sheathing tube. Light the pilot by manually depressing and holding down the valve knob or reset button to keep gas flowing to the pilot during the test. After the pilot has been lit for five or more minutes, the reading on the VOM/DMM should be 9 millivolts or higher. This indicates that the thermocouple is good. If the reading is less than 9 millivolts, the thermocouple is defective and must be replaced.

pic1 4 Thermocouple

No adapter is required to perform the thermocouple no-load test. First, the thermocouple is disconnected from the gas valve. Then the VOM/DMM is connected to the thermocouple. One meter lead is connected to the extreme end of the thermocouple lead and the other meter lead to the copper sheathing tube. Light the pilot by manually depressing and holding down the valve knob or reset button to keep gas flowing to the pilot during he test. After the pilot has been lit for five minutes, the reading on the VOM/DMM should be 18 millivolts or higher. This indicates that the thermocouple is probably good. If a reading of 18 millivolts or higher is not obtained, the thermocouple is defective and must be replaced.

14. May 2019 by matt
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MOTOR OPEN, SHORTED, OR GROUNDED CIRCUIT MEASUREMENT PROCEDURE

StepExpected Result/Action
6. Turn power off. Use the capocitor discharge tool (Figure SP-8-6) to discharge
the run capacitor and any other capacitors that may be used in the unit.
Locate the wiring connected to the motor windings. (Refer to the unit wiring
diagram.)
The wiring related to the motor is identified. All high-voltage capacitors used in
the equipment are discharged, including the run capacitor.
7. Isolate the motor from the remainder of the circuit by disconnecting the
motor leads from all the related components, including the run capacitor.
The motor leads are disconnected from other components to measure motor
resistance only.
8. Check the motor for shorted or open windings as follows:
Set up the VOM/DMM to measure resistance on the R x 1 ohm scale. If using
a VOM, make sure that it is zeroed. Connect one lead of the VOM/DMM to
the motor winding common lead as shown in Figure SP-10-8, View A. Touch
the other meter lead to the remaining motor leads, one lead at a time, and
observe the meter indication.
VOM/DMM indicates a measurable resistance for all measurements. When
measuring the motor run winding leads, the highest resistance is normally
measured between the common lead and the low (LO) speed run winding lead.
The lowest resistance is measured between the common lead and the high (HI)
speed run winding lead.
VOM/DMM indicates zero resistance for one or more measurements. This
indicates a completely shorted winding. Replace the motor.
VOM/DMM indicates infinity for one or more measurements. This indicates that
one or more motor windings are open. If checking a motor with an internal
motor protection device, make sure the motor has had adequate time to cool off
so that the protective device has reset. It may require an hour or more after the
motor has been turned off before the internal protection device resets. Replace
the motor if the motor is cool and the internal protection device has not reset.
9. Check the motor for grounded windings as follows:
Set up the VOM/DMM to measure resistance on the R x 10,000 ohm scale.
Connect one Eead of the VOM/DMM to a good ground connection, such as the
motor frame shown in Figure SP-10-8, View B. Poor electrical contact
because of a coat of paint, layer of dirt, or corrosion can cause an inaccurate
measurement and hide a grounded winding. Touch the other meter lead to
all of the motor leads, one lead at a time, and observe the meter indication.
VOM/DMM indicates infinity or high resistance. If a resistance reading is
indicated, it should not be less than 1,000 ohms per volt. For example, on a 230-
volt motor, the resistance should not be less than 230,000 ohms (230 volts x
1,000 ohms/volt = 230,000). This indicates that the motor windings are not
grounded.
VOM/DMM indicates low or zero resistance, or a measurable resistance that is
less than 1,000 ohms per volt. This indicates that the motor windings are
grounded. Replace the motor.

pic1 2 MOTOR OPEN, SHORTED, OR GROUNDED CIRCUIT MEASUREMENT PROCEDURE

14. May 2019 by matt
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Baxi Kingston 2 Cleaning the Burner and Injectors

1. Undo the screw retaining the spark electrode to the burner tray (Fig. 40).
2. Undo the screw retaining the burner to the burner tray (Fig. 41).
3. Slide the burner to the left to disengage from the injector. Rotate the electrode slightly and lift the burner out of the tray.
4. Using a soft brush remove any dirt from the burner and ensure all ports are free from obstruction.
5. Undo the union nut connecting the gas pipe to the injector (Fig. 40).
6. Undo the injector locknut and remove the injector from the burner tray by disengaging the gas pipe from the injector (Fig. 42).
7. Examine and clean the injector. Do not use any hard tools such as pins or wire. Renew if necessary (Fig. 42).
8. When re-tightening the gas feed pipe nut, hold the injector body with a suitable spanner to prevent misalignment of the injector.
9. Reassemble in reverse order.

Baxi Kingston 2 Cleaning the Burner and Injectors Baxi Kingston 2 Cleaning the Burner and Injectors

Applicable Models:

Baxi Wentworth PCF Classic
Baxi Kingston 2 PCF Classic
Baxi Belmont 2

13. May 2019 by admin
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Bent Tube Boilers

Bent tube boilers usually have three drums. The drums are usually of the same diameter and positioned at different levels with each other. The uppermost or highest positioned drum is referred to as the STEAM DRUM, while the middle drum is referred to as the WATER DRUM, and the lowest, the MUD DRUM. Tube banks connect the drums. The tubes are bent at the ends to enter the drums radially.

Water enters the top rear drum, passes through the tubes to the bottom drum, and then moves up through the tubes to the top front drum. A mixture of steam and water is discharged into this drum. The steam returns to the top rear drum through the upper row of tubes, while the water travels through the tubes in the lower rear drum by tubes extending across the drum and enters a small collecting header above the front drum.

Many types of baffle arrangements are used with bent-tube boilers. Usually, they are installed so that the inclined tubes between the lower drum and the top front drum absorb 70 to 80 percent of the heat. The water-tube boilers discussed above offer a number of worthwhile advantages. For one thing, they afford flexibility in starting up. They also have a high productive capacity ranging from 100.000 to 1,000,000 pounds of steam per hour. In case of tube failure, there is little danger of a disastrous explosion of the water-tube boiler. The furnace not only can carry a high overload, it can also be modified for tiring by oil or coal. Still another advantage is that it is easy to get into sections inside the furnace to clean and repair them. There are also several disadvantages common to water-tube boilers. One of the main drawbacks of water-tube boilers is their high construction cost. The large assortment of tubes required of this boiler and the excessive weight per unit weight of steam generated are other unfavorable factors.

12. May 2019 by admin
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Vertical-Tube Boiler

In some fire-tube boilers, the tubes run vertically, as opposed to the horizontal arrangement in the Scotch boiler. The VERTICAL-TUBE boiler sits in an upright position, as shown in figure 1-3. Therefore, the products of combustion (gases) make a single pass, traveling straight up through the tubes and out the stack. The vertical fire-tube boiler is similar to the horizontal fire-tube boiler in that it is a portable, self-contained unit requiring a minimum of floor space. Handholds are also provided for cleaning and repairing. Though self-supporting in its setting (no brickwork or foundation being necessary), it MUST be level. The vertical fire-tube boiler has the same disadvantages as that of the horizontal-tube design—limited capacity and furnace volume.

Before selecting a vertical fire-tube boiler, you must know how much overhead space is in the building where it will be used. Since this boiler sits in an upright position, a room with a high ceiling is necessary for its installation.

The blowdown pipe of the vertical tire-tube boiler is attached to the lowest part of the water leg. and the feedwater inlet opens through the top of the shell. The boiler fusible plug is installed either (1) in the bottom tube sheet or crown sheet or (2) on the outside row of tubes, one third of the height of the tube from the bottom.

Vertical Tube Boiler Vertical Tube Boiler

11. May 2019 by admin
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RUN CAPACITOR MEASUREMENT PROCEDURE

pic1 1 RUN CAPACITOR MEASUREMENT PROCEDURE

StepExpected Result/Action
1. Turn off all power to unit. Use the capacitor discharge tool {Figure SP-8-6) to
discharge the run capacitor and any other high-voltage circuit capacitors that
may be used in the unit.
All high-voltage capacitors used in the equipment are discharged, including the
run capacitor(s).
2. Locate and disconnect the wires from the run capacitor to isolate it from the
remainder of the circuit. {Refer to the unit wiring diagram.) Inspect the
capacitor for any visible signs of damage, such as bulging or leaking.
The run capacitor is isolated from the remainder of the circuit and prepared for
measurement. If the visual inspection reveals a bulged or leaking capacitor, it
should be considered bad and must be replaced.
3. Set up the VOM/DMM to measure resistance on the R x 1,000 or R x 10,000
ohm scale. Connect the VOM/DMM across the capacitor terminals and
measure the resistance as shown in Figure SP-10-7.
VOM/DMM reading first indicates zero or a low resistance, then slowly rises
toward infinity or some high value of measurable resistance. This indicates that
the capacitor is most likely good. If it is necessary to find out the capacitor's exact
capacitance value, it must be tested further using a capacitor tester per step 5.
VOM/DMM reading goes to zero or a low resistance and stays there. This
indicates that the capacitor is shorted. Replace the capacitor.
VOM/DMM reading indicates infinity. This indicates that the capacitor is open.
Replace the capacitor.
4. If testing a run capacitor enclosed in a metal case, check for a grounded
capacitor. Set up the VOM/DMM to measure resistance on the R x 1,000 or
R x 10,000 ohm scale. Connect the VOM/DMM between each one of the
capacitor terminals and the metal case and measure the resistance.
VOM/DMM reading indicates infinity. This indicates that the capacitor is not
grounded to the case.
VOM/DMM reading indicates a measurable resistance. This indicates that the
capacitor is grounded to the case. Replace the capacitor.
5. To measure a capacitor's exact capacitance MFD value, test the capacitor
using a capacitor tester. Follow the tester manufacturer's instructions to
perform the test.
The measured value for a run capacitor should be ±10% of the value shown on
the capacitor. If the value is not within these limits, replace the capacitor.

01. May 2019 by matt
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Electric Motor Capacitor Checks and Replacement

Capacitor Checks and Replacement Start and run circuits on single-phase motors use capacitors. Capacitors affect the wattage, amperage draw, torque, speed, efficiency, and power factor o f a motor. Figure SP-10-6 shows a typical run capacitor used with a PSC motor.

pic1 Electric Motor Capacitor Checks and Replacement

Ran capacitors are connected in the PSC motor circuit at all times and are therefore referred to as continuous-duty capacitors. Older run capacitors are usually larger in physical size, but have lower capacitance ratings than start capacitors. Newer ones may be smaller in physical size and encased in hard plastic shells. Because run capacitors are in the circuit at all times, they are typically filled with a dielectric fluid that acts to dissipate heat. If a capacitor is found to be defective, it should always be replaced with one specified by the manufacturer.

A run capacitor may be bulged and/or leaking, giving a visual indication of its failure. Testing of capacitors to determine if they are good or bad is commonly done by making resistance checks using a VOM/DMM. This method is described in the detailed procedure given at the end of this section. A capacitor analyzer should be used when accuracy is required in checking the electrical condition of the capacitor, especially when it is necessary to measure the actual capacitance MFD value of a capacitor. Note that some DMMs also have a capability to measure the actual capacitance MFD value of capacitors.

01. May 2019 by matt
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