Routine Maintenance: Residential Systems : Chapter 2
Content
Electrical Components - Part 1
In this module, we will take a look at common electrical inspections. We will look at how to inspect and replace the motor. Skip to quiz!
Inspecting Wiring
Electrical inspection refers to the complete check-up of the electrical components in HVAC systems. This includes inspecting the wiring of the components as well as their working.
Recall that electrical components are connected to each other using wires to form a complete circuit. These wires are made of copper and are covered with an insulating material. If there is no insulation, we might get shocked.
A short circuit is an unwanted connection between two points in the electrical circuit. A short circuit occurs when uninsulated wires touch. This may cause a fire. When current flows via unwanted paths, it can cause electrical fires and many other problems.
We also inspect the system for overloading. Overloading occurs when many electrical components are connected across two points in a circuit. Overloading means excess current passes through a single wire.
Too much current causes heat generation in the electrical circuit. This can melt the wires, with a risk of starting a fire. Compare this to a situation where too many cars go through a thin lane.
This will cause traffic congestion and accidents.
Earthing is the process of transferring unwanted electricity to the earth through a wire. We remain safe as all unwanted electricity is transferred to the earth, We give earthing to electrical systems to protect the system and the user from an electric shock.
We can find green and yellow earth wire that is connected to the metal casing of the air conditioner. The green and yellow wire is the earthing wire. We inspect the earthing of the system using a multimeter.
We check earthing resistance with a digital multimeter. Recall that we insert the black probe into COM and red probe into VΩ of the multimeter to test resistance. As we are performing the earth resistance test, we need to turn the selecting knob to the required range in Ω symbol.
We have to place one of the leads on the electric system body and the other on earth wire.
If the electric system is connected to earthing, it will show less resistance, or it will show infinite resistance. A good electric system should show a resistance value less than 0.5 ohms.
We check for any dust or dirt on the wiring connections. If there is any dust or dirt on them, we need to clean it by blowing air with a blower. Keeping the wiring connections clean will help eliminate any electrical problems.
Recall that the blower motor and compressor in the HVAC system vibrate when they are working. The vibration of the motor causes the wiring connections to loosen.
Loose connections can disconnect the power supply and stop the system. They can also cause a fire hazard. During any routine maintenance, we have to tighten all the wiring connections with a screwdriver.
Inspecting Motor
Recall that a motor uses electricity to rotate. In residential HVAC systems, compressor motor, condenser fan motor, and evaporator blower motor are found. HVAC systems depend on motors to move air, pump water, and run compressors.
Single-phase motors are commonly used in residential HVAC systems. There are several types single phase motors. Common terminals in all motors are:
Start Winding
Run Winding
Common connection
When we inspect motors, we perform:
General inspection,
Earth resistance test,
Power supply test,
Winding resistance test, and
Running amps test.
Let’s dive into the details about these inspections.
General inspections include visually inspecting the motor if it is burnt or damaged. Next, we manually rotate fan blades and observe for smooth and free rotation. Finally, we check the wiring connections if there is any loose or damaged wire.
If the fan blades do not rotate freely, we have to lubricate the fan motor. Lubrication is an action of applying oil or grease to the motor to minimize friction and allow smooth movement.
Let us see how to lubricate the condenser fan motor.
For lubricating the condenser fan motor, we have to switch off the condensing unit and remove the condenser fan motor. We pour the lubrication oil through the hole in the motor.
Finally, we rotate the fan blades with hand for checking smooth and free rotation of the motor.
For further inspection of the motor, we need a digital multimeter. Recall that we insert the black probe into COM and red probe into VΩ of the multimeter to test resistance. As we are performing the earth resistance test, we need to turn the selecting knob to the required range in Ω symbol.
We have to place one of the leads on the motor body and the other on earth wire. A good motor should show a resistance value less than 0.5 ohms. Any value greater than 0.5 ohms indicates that there is a problem with the motor.
As we are performing a power supply test, we need to turn the selecting knob to the required range in V∿ symbol. We have to place red lead on the positive terminal and black lead on the negative terminal of the incoming power supply. We can see the voltage reading in the display of the multimeter.
We need to compare this voltage with the specified voltage on the nameplate. The applied voltage should be within the range of the specified voltage. If it is much higher or lower than the specified voltage, this may be one of the sources of the problem.
Before performing this test, we need to disconnect the power supply to the motor. In this test, we check the resistance between the three terminals of a motor. Recall that Start(S), Common(C), and Run(R) are the three terminals in single phase motor.
We have to check the winding resistance, as shown in the video. As a rule of single-phase motors, the resistance value of:
S to R should be the highest,
R to C should be the lowest, and
C to S should be between the above two values.
The resistance value of S to R should be equal to the sum of R to C and C to S.
This test determines how much current is drawn to rotate the motor. We preferably use a clamp meter for this test. Recall that a clamp meter is a type of multimeter that measures current without in contact with the wiring.
We need to check the full load amps (FLA), as shown in the video. The FLA represents the maximum amount of current that should be drawn by the motor. The FLA is written on the nameplate of the motor.
The current drawn by the motor should not be above the specified FLA value. It should be at or slightly below the given FLA on the nameplate. If the motor draws current more than the FLA, it means the motor is damaged.
Replacing Motor
We have seen how to inspect a motor so far. Now we will learn how to replace a damaged motor. Let us look into how to replace a condenser fan motor.
For replacing the condenser fan motor, first we need to disconnect the power to the condensing unit to open the fan grill. Then we disconnect the fan motor wires from the capacitor and contactor in the access panel.
We have to transfer the fan blades from the old motor to the new motor. We have to attach the new fan motor to condensing unit and reconnect the wires, as shown in the video. Finally, we have to check the working of the fan motor by switching on the condensing unit.
Electrical inspection includes inspecting the wiring of the components as well as their working. We check for dust or dirt, insulation, loose connections, and earthing during wiring inspection.
When we inspect motors, we perform:
General inspection,
Earth resistance test,
Power supply test,
Winding resistance test, and
Running amps test.
We have to replace the motor if it is damaged.
Electrical Components - Part 2
In this module, we will look at how to inspect and replace- capacitor, contactor, and relay.
We will look at how to inspect a motor starter. Skip to quiz!
Inspecting Capacitor
Recall that capacitor is a device that stores and supplies electrical energy. It is similar to a rechargeable battery but charges and discharges much quicker. It is attached to the compressor motor, fan motor, or blower motor.
A single run capacitor is connected to a single motor. It has two terminals, HERM and COM.
The two wires that come from the motor can connect to either terminal.
The dual run capacitor is able to support two motors, such as compressor motor and fan motor, in the outdoor unit. It has three terminals:
HERM - connects to the compressor,
FAN - connects to the fan motor, and
COM - connects to the contactor.
Recall that the capacitor stores energy. One of the initial steps during the inspection is to discharge the capacitor. To discharge the capacitor, we connect the two terminals using a screwdriver.
We turn the multimeter selecting knob to the capacitance “-|(- section” for measuring capacitance. Recall that we measure the capacitance by touching the red probe to HERM and the black probe to COM.
The measured capacitance value should be within the range specified by the manufacturer. Any value out of the range indicates a problem with the capacitor. We need to replace such a capacitor.
Replacing Capacitor
We must turn off the power before changing the capacitor. Next, we have to open the access panel and locate the capacitor. We need to pull the wires connected to the capacitor. We have to discharge and remove the old capacitor.
We position the new capacitor in the place of the old capacitor. Then we connect the wires to the correct terminals of the new capacitor. Finally, we turn the power back on and inspect it.
Inspecting Contactor
Recall that a contactor is an electrical component that is used to switch an electrical circuit on or off. Contactors are mostly used for controlling electric motors. They supply power to the motor when the contactor coil is closed.
To test the contactor, we need to take out the contactor from the condenser unit. For that, we have to disconnect the power supply to the HVAC system. Then we have to remove the access panel of the condenser unit and take a picture of the wiring of the contactor.
Then we need to remove the wiring connections of the contactor and unscrew it. Now we have to check the contactor with a multimeter, as shown in the video.
Replacing Contactor
We need to turn off the power supply to the condenser unit before starting the procedure. Then we have to remove the access panel and take a picture of the wiring of the contactor.
We have to remove the old contactor and replace the new contactor, as shown in the video.
Inspecting Relay
Recall that a relay also is an electrical component that is used to switch an electrical circuit on or off. A relay works the same as the contactor, but it is small in size. It is connected to smaller loads like fan motor and blower motor.
We have to check the resistance between each pole of the relay, as shown in the video. When the relay is de-energized, all contacts should read infinite ohms to the corresponding pole. When the relay is energized, all contacts should read zero ohms to the corresponding pole.
Replacing Relay
Recall that relay is similar to the contactor but small in size. The replacement of relays follows the same procedure as we did for a contactor.
Inspecting Motor Starter
Recall that a motor starter is an electrical device used to start and stop a motor safely. It is also similar to a contactor, but it provides low voltage and overcurrent protection. It is usually connected to large three-phase motors.
First, we have to inspect the supply line voltage and control voltage with a multimeter.We have to reset the overload by pressing the red button on the starter. The overload is designed to protect the motor if the current exceeds the full load amps(FLA).
If resetting the overload does not work, we must disconnect the power and check the continuity between the two normally closed (NC) terminals. If the multimeter shows infinite resistance, there is no continuity, and the current does not flow through it. This means the overload is bad and should be replaced.
If the overload shows continuity between the two NC terminals, we’ll have to dig in a bit further. We have to measure the FLA and compare with manufacturer’s specified value.
FLA should be within range of the specified value.
Lastly, we check continuity across fuses of motor starter with the multimeter. If any fuse is blown, we have to replace it.
We have to discharge the capacitor before inspecting it. The measured capacitance value of the capacitor should be within the range specified by the manufacturer. To test the contactor, we need to take out the contactor from the condenser unit.
We have to remove the old contactor and replace the new contactor if it is damaged. The relay works the same as the contactor but it is small in size. A motor starter is also similar to a contactor, but it also provides low voltage and overcurrent protection.
Question #1: What reduces the risk of electric shock?
Earthing
Short circuit
Overloading
Loose connections
Scroll down for the answer...
Answer: Earthing
We would get an electric shock if the live wire inside the HVAC system came loose and touched the metal casing. However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock.
Question #2: In which test we measure the voltage applied to the motor?
Earth resistance test
Power supply test
Running amps test
Winding resistance test
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Answer: Power supply test
We measure the voltage applied to the motor with multimeter. This voltage should not much higher or lower than the specified voltage on the nameplate.
Question #3: What is the first step for the replacement of the condenser fan motor?
disconnect fan motor wires in the access panel
transfer the fan blades from the old motor to the new motor
disconnect the power to condensing unit
open the fan motor grill
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Answer: disconnect the power to condensing unit
Before starting the procedure, we have to disconnect the power supply to the condensing unit. Otherwise, it can cause electric shocks.
Question #4: A dual run capacitor is connected to two motors.
True
False
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Answer: True
The dual run capacitor is able to support two motors, such as compressor motor and fan motor, in the outdoor unit.
Question #5: During capacitor inspection, what do we measure with the multimeter?
current
voltage
resistance
capacitance
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Answer: capacitance
During capacitor inspection, what do we measure capacitance of the capacitor with the multimeter.The measured capacitance value should be within the range specified by the manufacturer. Any value out of the range indicates a problem with the capacitor.
Question #6: What do we need to open to locate the capacitor?
Fan grill
Access panel
Disconnect box
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Answer: Access panel
We have to open the access panel and locate the old capacitor while replacing it with new capacitor.
Question #7: What instrument is used to unscrew the contactor?
Cutting plier
Screwdriver
Hammer
Wrench
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Answer: Screwdriver
A screwdriver is used to unscrew the contactor from access panel.
Question #8: During relay inspection, what do we measure with the multimeter?
current
voltage
resistance
capacitance
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Answer: resistance
During relay inspection, we have to check the resistance between each pole of the relay. When the relay is de-energized, all contacts should read infinite ohms to the corresponding pole. When the relay is energized, all contacts should read zero ohms to the corresponding pole.
Question #9: Replacing relay follows same procedure as _______ .
Capacitor
Contactor
Fan motor
Compressor
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Answer: Contactor
Recall that relay is similar to the contactor but small in size. The replacement of relays follows the same procedure as we did for a contactor.
Question #10: Motor starter provides low voltage and overcurrent protection.
True
False
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Answer: True
A motor starter is an electrical device used to start and stop a motor safely. It is also similar to a contactor, but it provides low voltage and overcurrent protection. It is usually connected to large three-phase motors.
Question #11: What is connected to large three-phase motor to start and stop it safely?
Contactor
Motor starter
Relay
Capacitor
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Answer: Motor starter
Recall that a motor starter is an electrical device used to start and stop a motor safely. It is also similar to a contactor, but it provides low voltage and overcurrent protection. It is usually connected to large three-phase motors.