Air-Handling Equipment

Air-handling equipment is available as packaged equipment in many configurations using any desired method of cooling, heating, humidification, filtration, etc. In large systems (over 25 m3/s), airhandling equipment is usually custom-designed and fabricated to suit a particular application. Air handlers may be either centrally located or decentralized.

Central Mechanical Equipment Rooms (MER). Usually the type of facility determines where the air-handling equipment is located. Central fan rooms today are more common in laboratory or industrial facilities, where maintenance is kept isolated from the conditioned space.

Decentralized Mechanical Equipment Rooms. Many office buildings locate air-handling equipment at each floor. This not only saves floor space for equipment but minimizes the space required for distribution ductwork and shafts. The reduced size of equipment as a result of duplicated systems allows the use of less expensive packaged equipment and reduces the need for experienced operating and maintenance personnel.

12. June 2019 by Jack
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Air Handling Unit

The basic secondary system is an all-air, single-zone, air-conditioning system consisting of an air-handling unit and an air distribution system. The air-handling unit may be designed to supply a constant air volume or a variable air volume for low-, medium-, or high-velocity air distribution. Normally, the equipment is located outside the conditioned area in a basement, penthouse, or service area. It can, however, be installed in the area if conditions permit. The equipment can be adjacent to the primary heating and refrigeration equipment or at considerable distance from it by circulating refrigerant, chilled water, hot water, or steam for energy transfer.

Figure 1 shows a typical draw-through central system that supplies conditioned air to a single zone or to multiple zones. A blowthrough configuration may also be used if space or other conditions dictate. The quantity and quality of supplied air are fixed by space requirements and determined as indicated in Chapters 27 and 28 of the 1997 ASHRAE Handbook—Fundamentals. Air gains and loses heat by contacting heat transfer surfaces and by mixing with air of another condition. Some of this mixing is intentional, as at the outdoor air intake; other mixing is the result of the physical characteristics of a particular component, as when untreated air passes through a coil without contacting the fins (bypass factor).

pic1 28 Air Handling Unit

All treated and untreated air must be well mixed for maximum performance of heat transfer surfaces and for uniform temperatures in the airstream. Stratified, parallel paths of treated and untreated air must be avoided, particularly in the vertical plane of systems using double inlet or multiple-wheel fans. Because these fans do not completely mix the air, different temperatures can occur in branches coming from opposite sides of the supply duct.

12. June 2019 by Jack
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Temperature Versus Air Quantity

Designers have considerable flexibility in selecting the supply air temperature and corresponding air quantity within the limitations of the procedures for determining heating and cooling loads. ASHRAE Standard 55 also addresses the effect of these variables on comfort. In establishing the supply air temperature, the initial cost of lower airflow and low air temperature (smaller fan and duct systems) must be calculated against the potential problems of distribution, condensation, air movement, and the presence of increased odors and gaseous or particulate contaminants. Terminal devices that use low-temperature air can reduce the air distribution cost. These devices mix room and primary air to maintain reasonable air movement in the occupied space. Because the amount of outside air needed is the same for any system, the percentage in low temperature systems is high, requiring special care in design to avoid freezing of preheat or cooling coils. Also, the low-temperature air supply reduces humidity in the space. Lower humidity during cooling cycles costs more in energy because the equipment runs longer. Also, if the humidity is too low, it may cause respiratory problems.

12. June 2019 by Jack
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Space Heating

Although steam is an acceptable medium for central system preheat or reheat coils, low-temperature hot water provides a simple and more uniform means of perimeter and general space heating. Individual automatic control of each terminal provides the ideal space comfort. A control system that varies the water temperature inversely with the change in outdoor temperature provides water temperatures that produce acceptable results in most applications. To produce the best results, the most satisfactory ratio can be set after the installation is completed and actual operating conditions are ascertained.

Multiple perimeter spaces on one exposure served by a central system may be heated by supplying warm air from the central system. Areas that have heat gain from lights and occupants and no heat loss require cooling in winter, as well as in summer. In some systems, very little heating of the return and outdoor air is required when the space is occupied. Local codes dictate the amount of outside air required (see ASHRAE Standard 62 for recommended optimum outside air ventilation). For example, with return air at 24°C and outside air at -18°C, the temperature of a 25% outdoor/75% return air mixture would be 13°C, which is close to the temperature of the air supplied to cool such a space in summer. In this instance, a preheat coil installed in the minimum outdoor airstream to warm the outdoor air can produce overheating, unless it is sized so that it does not heat the air above 2 to 5°C. Assuming good mixing, a preheat coil located in the mixed airstream, prevents this problem. The outdoor air damper should be kept closed until room temperatures are reached during warm-up. A return air thermostat can terminate the warm-up period.

When a central air-handling unit supplies both perimeter and interior spaces, the supply air must be cool to handle the interior zones. Additional control is needed to heat the perimeter spaces properly. Reheating the air is the simplest solution, but it is not acceptable by most energy codes. An acceptable solution is to vary the volume of air to the perimeter and combine it with a terminal heating coil or a separate perimeter heating system, either baseboard, overhead air heating, or a fan-powered terminal unit with supplemental heat. The perimeter heating should be individually controlled and integrated with the cooling control. Resetting the supply water temperature downward when less heat is required generally improves temperature control.

12. June 2019 by Jack
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Zoning – Exterior

Exterior zones are affected by varying weather conditions wind, temperature, and sun and, depending on the geographic area and season, may require both heating and cooling at different times. While the engineer has many options in choosing a system, the system must respond to these variations. The considerable flexibility to meet such variations enables the greatest advantages from VAV systems to be realized. The need for separate perimeter zone heating is determined by
• Severity of the heating load (i.e., geographic location).
• Nature and orientation of the building envelope.
• Effects of downdraft at windows and the radiant effect of the cold glass surface (i.e., type of glass, area, height, and U-factor).
• Type of occupancy (i.e., sedentary versus transient).
• Operating costs (e.g., in buildings such as offices and schools that are unoccupied for considerable periods, fan operating cost can be reduced by heating with perimeter radiation during unoccupied periods rather than operating the main supply fans or local unit fans.)

Separate perimeter heating can operate with any all-air system. However, its greatest application has been in conjunction with VAV systems for cooling-only service. Care in design minimizes simultaneous heating and cooling. The section on Variable Air Volume has further details.

12. June 2019 by Jack
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All-Air System

An ALL-AIR SYSTEM provides complete sensible and latent cooling, preheating, and humidification capacity in the air supplied by the system. No additional cooling or humidification is required at the zone, except in the case of certain industrial systems. Heating may be accomplished by the same airstream, either in the central system or at a particular zone. In some applications, heating is accomplished by a separate heater. The term zone implies the provision of, or the need for, separate thermostatic control, while the term room implies a partitioned area that may or may not require separate control.

The basic all-air system concept is to supply air to the room at such conditions that the sensible heat gain and latent heat gain in the space, when absorbed by the supply air flowing through the space, will bring the air to the desired room conditions. Since the heat gains in the space will vary with time, a mechanism to vary the energy removed from the space by the supply air is necessary. There are two such basic mechanisms: vary the amount of supply air delivered to the space, either by varying the flow rate or supplying air intermittently, or vary the temperature of the air being delivered to the space, either by modulating the temperature or conditioning the air intermittently.

All-air systems are classified in two categories:

• Single-duct systems, which contain the main heating and cooling coils in a series flow air path; a common duct distribution system at a common air temperature feeds all terminal apparatus. Either capacity varying mechanism (varying temperature or varying volume) can be used with single-duct systems.
• Dual-duct systems, which contain the main heating and cooling
coils in parallel flow or series-parallel flow air paths with either (1) a separate cold and warm air duct distribution system that blends the air at the terminal apparatus (dual-duct systems), or (2) a separate supply air duct to each zone with the supply air blended to the required temperature at the main unit mixing dampers (multizone). Dual-duct systems generally vary the supply air temperature by mixing two airstreams of different temperatures, but can also vary the volume of supply air in some applications.

These categories may be further divided as follows:

Single duct
Constant volume
Single zone
Multiple-zone reheat
Bypass VAV
Variable air volume (VAV)
Throttling
Fan-powered
Reheat
Induction
Variable diffusers
Dual duct
Dual duct
Constant volume
Variable air volume
Dual conduit
Multizone
Constant volume
Variable air volume
Three-deck or Texas multizone

All-air systems may be adapted to many applications for comfort or process work. They are used in buildings that require individual control of multiple zones, such as office buildings, schools and universities, laboratories, hospitals, stores, hotels, and even ships. All air systems are also used virtually exclusively in special applications for close control of temperature and humidity, including clean rooms, computer rooms, hospital operating rooms, research and development facilities, as well as many industrial/manufacturing facilities.

All-air systems have the following advantages:
• The location of the central mechanical room for major equipment allows operation and maintenance to be performed in unoccupied areas. In addition, it allows the maximum range of choices of filtration equipment, vibration and noise control, and the selection of high quality and durable equipment.
• Keeping piping, electrical equipment, wiring, filters, and vibration and noise-producing equipment away from the conditioned area minimizes service needs and reduces potential harm to occupants, furnishings, and processes.
• These systems offer the greatest potential for use of outside air for economizer cooling instead of mechanical refrigeration for cooling.
• Seasonal changeover is simple and adapts readily to automatic control.
• A wide choice of zoning, flexibility, and humidity control under all operating conditions is possible, with the availability of simultaneous heating and cooling even during off-season periods.
• Air-to-air and other heat recovery may be readily incorporated.
• They permit good design flexibility for optimum air distribution, draft control, and adaptability to varying local requirements.
• The systems are well suited to applications requiring unusual exhaust or makeup air quantities (negative or positive pressurization, etc.).
• All-air systems adapt well to winter humidification.
• By increasing the air change rate and using high-quality controls, it is possible for these systems to maintain the closest operating condition of ±0.15 K dry bulb and ±0.5% rh. Today, some systems can maintain essentially constant space conditions.

All-air systems have the following disadvantages:
• They require additional duct clearance, which reduces usable floor space and increases the height of the building.
• Depending on layout, larger floor plans are necessary to allow enough space for the vertical shafts required for air distribution.
• Ensuring accessible terminal devices requires close cooperation between architectural, mechanical, and structural designers.
• Air balancing, particularly on large systems, can be more difficult.
• Perimeter heating is not always available to provide temporary heat during construction.

12. June 2019 by Jack
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AIRFLOW MEASUREMENT IN A FAN COIL WITH ELECTRIC HEAT

StepExpected Result/Action
1. Drill a hole in the return air duct near the fan coil as shown in Figure
SP-15-2. Drill a second hole in the supply air duct out of the line of sight of
the heating elements to prevent radiant heat from affecting the readings.
Holes drilled in the supply and return air ducts in preparation for measurement.
2. Turn on power to the fan coil and set the thermostat to call for heat. Allow it
to run about ten minutes to stabilize the temperatures. Set the thermostat
high enough to cause the fan coil to run continuously during the measurement.
Fan coil on and temperatures stabilized.
3. Using the electronic thermometer, measure and record the return and supply
air temperatures. Make sure the thermometer readings have stabilized for
the measurement.
Supply and return air temperatures measured and recorded.
For our example assume:
Supply temperature = 1 0 0 ° F
Return temperature = 7 2 ° F
4. Using the measured values of supply and return temperatures, calculate the
temperature rise using the formula below:
Supply Temperature - Return Temperature = Temperature Rise
Temperature rise is calculated.
For our example assume:
100° F - 7 2 ° F = 2 8 ° F
5. Set up VOM/DMM to measure AC volts. Select a range high enough to
measure the fan coil input voltage. At the unit disconnect box or unit
terminal board, measure and record the input voltage as shown in
Figure SP-15-3.
Input voltage measured and recorded.
For our example assume:
The measured input voltage is 2 3 0 volts.
6. Set up the clamp-on ammeter to measure current on the highest range scale.
Measure and record the total current of the air handler as shown in Figure
SP-15-3.
Input current measured and recorded.
For our example assume:
The measured current is 4 5 amperes.

pic1 25 AIRFLOW MEASUREMENT IN A FAN COIL WITH ELECTRIC HEAT

Purpose – This procedure describes how to calculate the quantity of airflow in cubic feet per minute (CFM) being delivered by a fan coil containing electric heating elements. Having the correct quantity of airflow is important in order to maintain heating comfort in the conditioned space and for efficient and safe equipment operation. Airflow measurements are normally made when a fan coil is initially installed and when troubleshooting.

Calculating Airflow
The volume of airflow in a fan coil with electric heat can be calculated using measured values for the amount of temperature rise across the heating elements, along with the input voltage and the total (including blower motor) current flow through the air handler. Temperature rise is the difference between the return air temperature entering and the supply air temperature leaving the fan coil. While the measurements are being taken, the system must run continuously. The method for calculating airflow, including a typical example, is provided in the detailed procedure at the end of this section and briefly outlined here.

Before making any measurements, check that the air filter is clean, all supply and return registers are open and unrestricted, and that any zone dampers are fully open. Also, let the system run long enough to make sure the system temperatures have stabilized.

After the system is stabilized, the temperatures entering and leaving the unit are measured with an accurate electronic thermometer (Figure SP-15-1). N e x t, the temperature rise is calculated by subtracting the return air temperature from the supply air temperature. When measuring the discharge or supply air, the thermometer must be out of the line o f sight of the heater elements to prevent radiant heat from affecting the reading.

If the quantity of airflow in CFM is within the range specified by the equipment manufacturer, no adjustment of the airflow is required. If the flow is too low, the blower speed should be increased to increase the airflow. If it is too high, the blower speed should be decreased to decrease the airflow.

12. June 2019 by Jack
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COOLING SYSTEM PROPER AIRFLOW RANGE

StepExpected Result/Action
1. Drill a hole in the return air duct to measure the evaporator entering air
temperature as shown in Figure SP-14-3, View A. Drill a second hote in the
supply air duct to measure the evaporator leaving air temperature.
Holes drilled in the supply and return air ducts in preparation for measurement.
2. Turn on the power lo the system. Make sure that all the supply and return
registers are open. Allow the system to run for about ten minutes to stabilize
the temperatures. Set the thermostat low enough so that the system runs
continuously during the measurement.
System on and temperatures stabilized.
3. Using the electronic thermometer, measure and record the evaporator
entering air wet bulb and dry bulb temperatures. Make sure the thermometer
readings have stabilized for the measurement.
Evaporator entering air wet bulb and dry bulb temperatures measured and
recorded.
For our example assume:
Entering air wet bulb temperature = 6 4 ° F
Entering air dry bulb temperature = 7 6 ° F
4. Using the electronic thermometer, measure and record the evaporator
leaving air dry bulb temperature. Make sure the thermometer reading has
stabilized for the measurement.
Evaporator leaving air dry bulb temperature measured and recorded.
For our example assume:
Leaving air dry bulb temperature = 57° F
5. Using the proper airflow calculator, set the pointer to the indoor entering air
dry bulb °F measured in step 3.
For our example assume:
The pointer is a t7 6 ° F as shown in Figure SP-14-3, ViewB.
6. On the calculator, find the value for the indoor entering air wet bulb
temperature measured in step 3, then read the proper evaporator leavingair
temperature directly below it.
For our example assume:
The evaporator (indoor) wet bulb temperature of 64° F is found on the
calculator. Directly below it is the correct evaporator leaving air dry bulb
temperature, as shown in Figure SP-14-3, View C.
The proper evaporator leaving air dry bulb temperature is 5 7 ° F
and the actual evaporator leaving air temperature measured in
step 4 is 5 7 ° F. This means that the airflow is within the 4 0 0 to 450
CFM per ton range and no adjustment to the blower speed is needed.
A tolerance of ± 3 ° F is allowed.
If the evaporator leaving air temperature measured in step 4 is above 60° F
[proper evaporator leaving air dry bulb temperature of 57° F read from
calculator plus 3° F = 60° F), decrease the blower speed.
If the evaporator leaving air temperature measured in step 4 is below 54° F
(proper evaporator leaving air dry bulb temperature of 57° F read from
calculator minus 3° F = 54° F), increase the bfower speed.

pic1 22 COOLING SYSTEM PROPER AIRFLOW RANGE

Purpose — This procedure describes how to determine if airflow across the evaporator in a cooling system is adequate. For proper operation of a cooling system, the blower should be moving from 400 to 450 CFM of air across the evaporator coil for each ton of cooling capacity. For example, on a 2-ton cooling unit, the volume of air should be at least 800 CFM. Too much or too little air can cause indoor comfort problems as well as equipment problems. The airflow is normally measured when a cooling system is initially installed, being charged with refrigerant, or when troubleshooting.

Airflow Problems

Too much air across the evaporator coil results in poor humidity control. If air moves too fast across the evaporator, moisture is not effectively removed. To correct the problem of too much air, decrease the blower speed.

While too much air can be a problem, the problem of too little air is more widely seen. The usual symptom is a frozen evaporator coil. Refrigerant flooding can result from low airflow and this in turn may cause compressor failures. To correct the problem of too little air, increase blower speed. However, before adjusting the blower speed, always make sure that:
• The system air filter is clean.
• The blower wheel is clean.
• The evaporator coil is clean.
• There are no loose or worn belts on belt-driven blowers.
• The blower is rotating in the right direction.
• The system has the correct refrigerant charge.

Airflow Measurement
The procedure for measuring airflow given here uses the “Proper Airflow Range” section of the Required Superheat/Subcooling C a lc u la to r p rev iou sly used in S e rv ic e Procedure SP-4- This calculator is designed to provide a quick check to see if the airflow across the evaporator is adequate for proper cooling system operation. It cannot be used to find the actual air quantity in CFM. Methods for measuring actual CFM are shown in Service Procedures SP-15 through SP-17.

A detailed procedure and illustrated example for determining airflow using the Airflow Calculator is provided later in this section. A brief overview of the procedure and the use of the calculator follows.

After system operation has stabilized, the following temperatures are measured:
• Wet bulb and dry bulb of air entering the evaporator coil.
• Dry bulb of air leaving the evaporator coil.

The measured dry bulb and wet bulb temperatures for the air entering the evaporator are used with the calculator to find the proper evaporator coil leaving air dry bulb temperature. This step gives the correct leaving air temperature, assuming the system refrigerant charge is correct and the airflow across the coil is within the 400 to 450 CFM per ton range.

Following this, the actual dry bulb temperature of the air leaving the evaporator is compared with the value indicated by the calculator. Ideally, they should be the same. A tolerance of ± 3 ° F is allowed before any adjustment is required (Figure SP-14-2). If the actual air temperature leaving the evaporator is more than 3 ° F lower than the proper airflow temperature, the evaporator blower speed should be increased. If the actual air temperature leaving the evaporator is more than 3 ° F higher than the proper air temperature, the evaporator blower speed should be decreased.

12. June 2019 by Jack
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TEMPERATURE RISE MEASUREMENT IN A FOSSIL-FUEL FURNACE

StepExpected Result/Action
1. Drill a hole in the return air duct near the furnace as shown in Figure
SP-13-2. Drill a second hole in the supply air duct out of the line of sight of
the heat exchangers so that radiant heat does not affect the readings. This is
especially important with straight duct runs.
Holes drilled in the supply and return air ducts in preparation for measurement.
2. Turn on the power and gas to the unit. Allow the furnace to run about ten
minutes to stabilize the temperatures. Set the thermostat high enough to
allow the furnace to run continuously during the measurement.
Furnace on and temperatures stabilized.
3. Using the electronic thermometer, measure and record the return and supply
air temperatures. Make sure the thermometer readings have stabilized for
the measurement.
Supply and return air temperatures measured and recorded.
For our example assume:
Supply temperature = 128° F
Return temperature = 7 0 ° F
4. Using the measured values of supply and return air temperatures, calculate
the temperature rise using the formula:
Supply Temperature - Return Temperature = Temperature Rise
Temperature rise is calculated.
For our example assume:
128° F - 7 0 ° F = 5 8 ° F
5. Compare the measured temperature rise to the temperature rise range on
the furnace information plate.
If the temperature rise is within the range shown on the furnace information
plate, no adjustment of airflow is required. Ideally, however, the rise should be
slightly above the midpoint of the range. For example, with a temperature rise
range of 40° F to 70° F, the midpoint is 55° F.
For our example assume:
The temperature rise of 5 8 ° F falls slightly above the midpoint (55° F) of the
range of 4 0 ° F to 7 0 ° Fshown on the furnace information plate. This indicates
that the airflow is adequate and no airflow adjustment is needed.
If the temperature rise is too low, decrease the blower speed to decrease the
airflow. If the temperature rise is too high, increase the blower speed to increase
the airflow. Follow the furnace manufacturer's instructions for increasing or
decreasing the blower speed.

pic1 20 TEMPERATURE RISE MEASUREMENT IN A FOSSIL FUEL FURNACE

Purpose – This procedure describes how to measure the temperature rise in fossil-fuel furnaces. Temperature rise is the difference between the return air temperature entering the furnace, and the supply air temperature leaving the furnace. The amount of temperature rise gives an indication of whether adequate air is flowing across the furnace heat exchangers. However, it cannot determine air quantity. Temperature rise measurements are normally made when a furnace is initially installed and when troubleshooting furnaces.

Temperature Rise
The correct temperature rise range for a particular furnace can be found on the furnace information plate (Figure SP-13-1). The correct amount of temperature rise is critical in highefficiency furnaces. If too much air passes over the heat exchangers, condensing can take place in the heat exchangers or vent, causing corrosion and failure. If too little air passes over the heat exchangers, the resultant overheating may cause premature failure of the heat exchangers. If the temperature rise is too low or too high, the furnace’s blower speed must be changed to bring the rise into the desired range. Before making temperature rise measurements, make sure that:
• The furnace is fired at its full rated input.
• The furnace air filter is clean.
• All supply and return registers are open and unrestricted.
• If equipped with a bypass humidifier, the damper in the bypass duct must be closed.

Temperature Rise Measurement

The method for measuring temperature rise is provided in the detailed procedure at the end of this section and briefly outlined here.

Temperature measurement holes are drilled in the return air duct near the furnace and in the supply air duct out o f the line of sight of the heat exchangers (Figure SP-13-2). The furnace is turned on and o p e rate d for ab o u t ten minutes to allow the temperatures to stabilize.

The supply and return air temperatures are measured with an accurate thermometer, then the temperature rise is calculated by subtracting the return air temperature from the supply air temperature. Ideally, the temperature rise should be slightly above the midpoint of the range shown on the furnace information plate. If the temperature rise is too low, decrease the blower speed to reduce the airflow; if too high, increase the blower speed to increase the airflow.

11. June 2019 by Jack
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FAULT ISOLATION OF NON-REPAIRABLE ELECTRONIC CONTROLS

StepExpected Result/Action
1.
With power applied to the furnace, use any built-in component test feature
(if so equipped) to help isolate the cause of the problem. Refer to the
manufacturer's service instructions.
Many units are equipped with some form of indicator on the electronic control
that displays the unit's operating status and/or fault codes. Normally, a label is
attached to the unit that defines the operating status or fault associated for each
of the fault indication codes. Many units also are equipped with a built-in
component test feature to aid the service technician in isolating problems. When
the unit being serviced is so equipped, follow the manufacturer's instructions for
the use of the built-in diagnostic features and for troubleshooting the unit.
For our example assume:
You begin troubleshooting the unit based on your observation that the inducer
motor failed to run during the component test.
2.
Set the VOM/DMM to measure AC voltage. Note that the voltage level
expected is 24 volts. Connect the VOM/DMM meter leads across the
thermostat connection R and COM terminals as shown in Figure SP-12-4.
If the VOM/DMM indicates 24 VAC, this indicates that the 24 VAC control voltage
input to the electronic control is good. Proceed to step 3.
If the VOM/DMM reads 0 VAC, use the hopscotch method to isolate any open or
failed component or wiring. Check for the following:




Is power applied to the furnace?
Is the interlock (ILK) switch closed?
Is the fuse (FU1} on the control board good?
Is the flame rollout switch (FRS) or main limit switch (LS) open?
For our example assume:
The VOM/DMM indicates 24 VAC
3.
Connect the VOM/DMM meter leads across the thermostat connection W and
COM terminals as shown in Figure SP-12-4.
If the VOM/DMM reads 24 VAC, this indicates that the 24 VAC "call-for-heat"
input to the electronic control is good. Proceed to step 4.
If the VOM/DMM reads 0 VAC, use the hopscotch method to isolate any open or
failed component or wiring. Check for the following:



Is the thermostat function switch set in the heating mode?
Is the thermostat temperature set high enough?
Is the thermostat defective?
For our example assume:
The VOM/DMM indicates 24 VAC.
4.
Set the VOM/DMM to measure 115 VAC. Connect the VOM/DMM meter leads
across connector PL3 terminals 1 and 3 as shown in Figure SP-12-4.
The VOM/DMM reads 115 VAC but the inducer motor does not run. This indicates
that the 115 VAC output from the electronic control is good; therefore, the control
board is good. Use the hopscotch method to isolate any problem external to the
electronic control. Check for the following:




Are the electrical connections tight?
Is the inducer motor capacitor defective?
Is there some mechanical defect such as a jammed inducer wheel preventing
the motor from turning?
Is the motor hot, indicating the internal overload may
be open?
If the VOM/DMM reads 0 VAC, replace the control.
For our exam ple assume:
The VOM/DMM indicates J 15 VAC, indicating that the electronic control is good
Further, assume the problem is found to be a loose connection between the
electronic control and the inducer motor.

pic1 8 FAULT ISOLATION OF NON REPAIRABLE ELECTRONIC CONTROLS

10. June 2019 by Jack
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