Packaged Rooftop Units: Routine Maintenance: Chapter 2
Coils and Blower Motor
In this module, we will learn about routine maintenance procedures for different components in a packaged RTU. We will look at the maintenance of coils and motor assembly in detail. Skip to quiz!
Maintenance of Coils
Recall that the evaporator and condenser coils provide cooling and heating to a building. The refrigerant flows inside these coils. Heat is transferred from the refrigerant to the air as it flows over the coils.
Evaporator coils are installed vertically or slanted like a V shape in the RTU. Evaporator coils are always found above the blower motor or behind the dampers.
Condenser coils are generally present on the outer side of the RTU. Condenser coils come in all different types, shapes, and sizes.
Before starting the inspection, we first disconnect the power supply to the RTU. Find the access door on the RTU. Open it by pulling the door handle, or unscrew the bolts, including the fan grille.
After opening the access door, we need to check for debris and dust collected on the fins of the coils. If the dust is present, we will clean it using vacuum machine or brush.
Some of tools that are necessary to during a maintenance are:
Coil cleaner,
Small water pump,
Hose,
brush,
Detergents, and
Disinfectants.
We need to clean the debris collected at the bottom of the coils or inside the unit using a brush or vacuum.
Dirt on the coils is cleaned with the help of a soft brush or a hose with medium-pressure water jet. We use detergents or coil cleaner to wash the coils. Spray the coil cleaner on the coils and leave it for some time to settle down.
We then rinse the coils with a water hose from top to bottom. Use a soft brush to rub out any dirt has not been removed after rinsing the coils with water. Sometimes we would also need to clean the coils from the outside of the unit.
Finally, reassemble all the access doors and sheet panels, including the fan grill. Clean the area around the unit with water. Let us look at the video for cleaning of coils.
After cleaning the coils, we should inspect both the coils to look for any physical damages. The fins on the coils are usually fins are bent. We use a fin tool also called a fin comb to straighten the fins if they are bent.
The next step is to observe the copper tubing for leakage or damage. Also look for damaged insulation covering on the pipe. The refrigerant might leak and the RTU will stop providing cool or hot air if the refrigerant pipes are damaged. Damaged tubing might call for troubleshooting the unit.
Maintenance of Motor Assembly
Recall an electric motor is a machine that consumes electricity to provide mechanical rotation. The main types of electric motors are:
AC motors, and
DC motors
We mainly use an induction motor to drive the blower. It is a type of an AC motor. The motors are connected to the blower fan using different drives. Recall that a blower wheel has blades that are specifically designed to push air into conditioned spaces.
The types of drives used in RTU fans are:
Belt drives and
Direct drives.
A direct drive motor is connected directly to the blower on the same shaft. A belt drive motor is connected to the blower with a belt.
RTUs generally have two motors. One motor for indoor air supply and another for cooling condenser coils. We don’t inspect for direct drive motors, and it needs troubleshooting for any problem.
Inspecting the Motor Assembly
Before starting the inspection, we first disconnect the power supply to the RTU. We need to open the access door using the door handle or unscrew the bolts.
We first need to check for signs of corrosion and overheating. Any discoloration of motor assembly parts is a sign of corrosion. As soon as it is switched off, we need to touch the outer case of the motor to look for overheating of the motor.
Overheating of the motor may be caused due to the following reasons:
wrong voltage supply,
lack of ventilation,
wrong motor for the unit, or
overload on the motor.
All of these problems call for further troubleshooting of the complete unit.
Recall that relays are switches that open and close circuits electronically. They control the working of a motor. During maintenance, ensure that the relays and contacts are dust-free. It is good to clean the terminals with a brush after switching off the unit.
Recall that relay and contactors are checked using a multimeter. We will check the relay if the system is not working. This is a part of troubleshooting the unit. When connected to the relay terminals, the multimeter shows OL (open loop) or 1 when the relay is faulty; else, it should show some voltage.
Some of the processes while inspecting the motor assembly in an RTU include:
Checking for belt tension,
Checking for belt wear & tear,
Checking the pulley alignment, and
Checking the motor base and support.
In most RTUs, the motor & blower fan is connected via a belt. The belt is connected to the motor and rotates the blower fan. The condition of the belt decides if the motor can turn the fan blades. A tight belt will damage the motor, and a loose belt will not rotate the fan.
Recall that a belt is a loop of flexible material used to connect two rotating shafts. There are two major types of belts:
V-Belts and
Synchronous Belts.
V-Belts are the most basic belts used in RTU’s.
Use a belt tensioner gauge to check the tension in the belts. A belt tensioner gauge is a tool to check how much the belt moves when a small amount of force is applied. The movement has to be within limits as prescribed in the owner’s manual.
We also usually check the tightness of the belt. We do this by pushing down on the belt with a finger in the middle of the belt. The belt should not be too tight or too loose, but within limits as prescribed in the owner’s manual.
A good measure of tightness is that the belt should not go down more than a half-inch after pushing. If it goes beyond a half-inch, we will adjust the motor base and pulleys.
An old belt will have strings and threads come out of the belt. These are signs that the belt is old or damaged. Old belts will also have cracks on them. If the belt is has cracks or strings coming out, then it needs to be replaced.
The next step after you check the belt is to check its alignment. We need to check the alignment to see if the belt and pulleys are in a straight line. The belts can wear out more quickly when pulleys are not aligned properly.
Recall that pulleys are circular pieces of metal that have the belt on them and are connected to the motor and the blower fan. We should whether both the pulleys are in line. This is done by checking the alignment with a straight wood piece, thread, or long scale.
If the belt is not straight, we adjust the pulleys and the motor base. To adjust the pulley, we loosen the pulley key on the shaft using an allen key to move the pulley. This should loosen the pulley. Now adjust the pulley so that the belt remains tight and straight. If this does not work, we need to adjust the motor base.
The motor base is attached to the base of the RTU by bolts. We can loosen the bolts and align the motor to be in line. The base of the motor is slidable. We can slide the motor back and forth on the base to adjust the alignment.
If the points are not touching or the belt appears misaligned, slide the motor back and forth on the motor base. Now check if the belt and both pulleys are in line with a straight wood piece, thread, or long scale. Tighten the bolts on the base once you find the correct alignment.
Recall that lubrication is a process to reduce friction between two moving parts. Friction is the resistance to motion of between moving objects. Oil and grease are the most common substances used for lubrication. We apply oil or grease to the bearings.
We need to lubricate all the bearings in the RTU. These include the
Motor bearings,
Motor shaft,
Blower bearings, and
Bearing housing
Bearing housing is the outer part that provides support and connects the bearings to the RTUs body.
Inspection of condenser and evaporator coils consist of checking debris, dust, and damages on coils. Coils cleaning includes cleaning, spraying cleaners, and washing with water.
Inspecting the motor assembly in an RTU include:
Checking for belt tension,
Checking for belt wear & tear,
Checking the pulley alignment, and
Checking the motor base and support.
Lubrication of motor bearings help the motor assembly to run smoothly.
Inspecting other components - Part 1
In this module, we will learn about routine maintenance of packaged rooftop unit components. Let us look at inspecting and maintenance of compressor, gas burners, and drain. Skip to quiz!
Compressor
Recall that a compressor is an important equipment that acts upon the refrigerant to increase its pressure. During a routine maintenance, we will first turn off the unit and visually inspect the compressor. We should access the compressor by opening the door lever or unscrewing the bolts.
Look for oil stains around the compressor. If there is a oil stain, it mean that there is a refrigerant leak and troubleshooting might be needed.
We will visually inspect all the all the electrical connections, wires, capacitors, and relay. There should be no loose wires connected to any components. Inspecting the electrical connections will avoid sparks or burning of components.
Refrigerant Pressure
Recall that to check refrigerant pressures, we use a manifold gauge. While checking, we need to make sure that the manifold gauge valves are closed. We connect the blue hose to the high side and the red hose to the low side of the unit.
After connecting the hoses, we turn the RTU ON and let it run until readings on the gauge stabilize. We must take both pressure readings in the manifold gauge and compare them with the manufacturer’s specified values. If the RTU has a heat pump, we need to run the unit heat mode and repeat the same procedure.
If the pressure readings are too low, this means that the coil may have a refrigerant leak somewhere. We have to find the leak and repair it. There can also be other reasons for a low-pressure reading. Thorough troubleshooting might be needed to find the actual reason.
If the pressure reading compared to the manufacturer’s reading is too high, the condensing unit might be dirty. We have to clean both the coils and measure the readings again. If the readings are still too high, the RTU may need further troubleshooting.
Condensate Drain
Recall that water vapor condenses to water on all the cold parts of the RTU. Any condensation in the RTU collects in the drain pan located below the evaporator coils. This water offers a perfect environment for the growth of mold and fungus.
The condensate drain consists of a drain pan and a drain line. The water that drips off the cooling coil is collected in the drain pan. The condensate drain line moves the water out of the drain pan into a drain. A p-trap is attached to the drain line before the drain.
Recall that a P-trap is a curved pipe attached to the condensate drain line. Drained water is collected at the bottom of the curve P-trap. This water creates an air seal that prevents outside air from the drain from entering the RTU. P-trap is placed just outside the unit.
When we inspect the drain line, we also inspect the P-trap as it is attached to it. We do not inspect the P-trap separately. For inspecting the drain line, we first need to switch off the RTU.
We need to remove the access panel using the door lever or unscrew the bolts of the evaporator section. We then visually inspect the drain pan for leaks and water trapped due any clogs in the drain line. We also inspect for debris and clean the drain pan if it has any debris.
We first switch off the RTU to clean the drain line. We will clean the drain line using the water jet from the water point available on the roof or nearby. We point the water hose against the normal flow and wait till it clears down.
If the clog is still present, we will pour the distilled vinegar in the drain line. We pour the distilled vinegar through the opening and let the solution sit for half an hour. Distilled vinegar takes some time to react with the debris and mold inside the drain line.
We then clean the drain pan and flush the pipe with water to ensure it is clean and operating normally. Finally, we close the access door of the RTU.
Gas Burners
Recall that the burner is a section of the gas furnace where air and fuel are combined and burned with a flame. It produces the heat that warms the office areas of the RTU. Locate the burner section on the RTU, and open the access door.
While inspecting a burner, the first step is to observe the flames while the RTU is ON. The flames should be burning with a steady blue color flames. Yellow flames mean there are some problems in the heating system. It would call for further troubleshooting.
For further inspection of the burner, we need to turn off the power supply to the RTU. We then need to find the gas supply line that goes to the burner and close its valve. Closing the valve stops the gas supply. We can now safely inspect component without the hazard of a gas leak or fire.
We have to open the burner and check it visually, whether it is clean or not, and if any rust is formed on it. Burners usually clog up with dust, dirt, and lint from the air and block gas from entering the burners. As RTUs are on the roof out in the open, these checks are essential.
Recall that the burners are made of metal. So, rust can form on them. Rusty burners wear much faster and can be costly to replace. We have to clean the dirt and rust on the burners during the maintenance. Let us look at a video to learn how to clean the burners.
For cleaning the burner, we have to first shut off the power to the unit. We access the burner section using the access door or unscrewing the panels. We then need to turn off the gas supply line also, to gain access.
As seen in the video, we then remove the burners from the gas-fired assembly. We use a brass brush to clean the rust and soot from the burner’s face. Next, we blow compressed air to remove any debris stuck inside the burners.
Finally, put back the clean burners onto their places and reassemble everything. We turn the gas valve to an open position and switch on the gas. We make sure that the burners are working properly.
Compressor inspection includes visual inspection for oil stain and refrigerant leak. The refrigerant pressures are measured using a manifold gauge, connecting the red hose to the high side and the blue hose to the low side. Pressure readings are verified with the owner’s manual.
The condensate drain consists of a drain pan and a drain line with P-trap. We clean the condensate drain with any debris or clog, using a water jet or pouring the vinegar solution. While cleaning gas burners, we need to shut off the RTU and gas valve. Burners need to be cleaned and freed from dust and rust.
Inspecting other components - Part 2
In this module, we will learn about inspecting and maintenance of
-Economizer,
-Heat exchanger,
-TXV, and
-Electrical components of an RTU. Skip to quiz!
Economizers
Recall that an economizer is a device used to reduce energy consumption. Economizers use the cool air from outside of a building to cool the circulating air inside the building. Economizer works with the help of a controller which operates the dampers, thereby controlling airflow.
Economizer consist of
Dampers,
Filters,
Sensors, and
A controller.
Let us look at a video consisting of economizer components.
While inspecting, the first step is to access the economizer section by opening the access panel. Next, we will check the working of all the dampers. Recall that we inspect damper actuators and locking quadrant for their operation.
If the filters are filled with dust, they are cleaned or replaced. Recall that reusable filters are cleaned with water. Non-reusable filters need to be replaced if they are dirty. Once the dampers and filters are fine, we finally look at the main controller.
The controller regulates the position of the dampers when it receives the signal from the control board and sensors. The minimum fresh air required into the building is set using the Min Pos switch in the economizer controls.
The minimum position (Min Pos) switch screw is rotated clockwise to open and anticlockwise to close it. We rotate this switch to adjust the fresh air into a building. It is set during installation. We only adjust it in case of any customer requirements.
The exhaust (Exh) switch in the controls regulates the power supplied to the exhaust fan from 2V to 10V. The DCV set switch is used to set the airflow as per the CO2 sensor used in the economizer. The controller’s operation is checked using the owner’s manual and needs to verify the settings provided during installation.
We should visually inspect all the wires for any loose connections. We should tighten all the connections using pliers and screwdrivers if required. The sensors should be cleaned using a dry cloth and properly connected to the economizer controller.
Inspecting Heat Exchangers
Recall that the heat exchangers have hot burnt gases flowing inside them, which transfer heat using coils or plates. Hot air is blown into the coils of the heat exchanger, and outside air flows over it and heats up. The blower sends the heated air to the offices and rooms.
Access the heater section by opening the access door or sheet panel. They are generally located beside the gas furnace or electric heater in an RTU. While inspecting, we should do only a visual inspection of the heat exchanger, or else troubleshooting is required.
The visual inspection includes looking out for any:
cracks,
corrosion, and
vibrations.
We look for cracks on the tubes. Smoke from the burning gas can escape through cracks in the heat exchanger tubes and mix with the building air.
Cracks in the heat exchanger tubes can also fill up with dust particles present in the outside air. Dust particles can damage the coils when heated up. Also, water vapor in the air can stay in the cracks and rust the heat exchanger tubes.
Look out for any corrosion on the coil tubes as it can contaminate the fresh air flowing over them. We finally inspect for any vibrations while running the heater section as it can damage the equipment with time. Damaged heating coils may release the smoke mixing it with the building air.
Thermal Expansion Valve (TXV)
Recall that the common metering devices used in rooftop units are the thermal expansion valves (TXV) and electronic expansion valves (EEV). The TXV is used to control the amount of refrigerant released to the evaporator section.
Before inspecting TXV, we need to make sure the unit has been running for a minimum of 5 minutes. Let us see the inspection of TXV in different scenarios.
As seen in the video, TXV is located near the evaporator coil in the RTU. Remove the TXV sensing bulb from the suction line for inspection. For inspection, refrigerant pressure readings have to be taken in different situations.
Recall that the refrigerant pressure reading is taken using a manifold gauge. Recall that a manifold gauge is used to check the pressure readings and connected as shown in the video. Check the high side pressure while holding the sensing bulb in your palm; the pressure should drop.
Again, check the high side pressure while putting the sensing bulb in cold water; the pressure should increase. If there's no change, that's an indication of a TXV problem, and troubleshooting is needed. Another instance to inspect TXV is checking the amp (current) drawn by the compressor.
The amp drawn by the compressor also depends on TXV operation. We measure the amp draw by holding a clamp meter across the compressor wires. The conditions of the TXV are
High amp drawn for fully open, and
Less amp drawn for a stuck, closed, or faulty TXV.
Controls
A control board is an electrical component that receives and sends all the signals through a programmed chip. Control boards differ from one manufacturer to another. All the sensors and actuators work as per the electrical signal sent and received by the control board.
Some sensors used in an RTU are,
Temperature sensor: It measures the temperature of heat or even cold air generated in the system.
Humidity sensor: It detects and measures the amount of water vapor or moisture contained in the air
Temperature control switch: The temperature sensor sends the signal after reaching the desired state then the control switch cuts off the unit from running.
Motorized actuator: These controls the dampers are closed and open upon signals sent through the board.
As seen in the video, electrical parts are needed to check for voltage, amperage, and conductivity. We first visually check all the connections are tight and no loose wires are present. We then check the relay, capacitor, and amperage consumption by using a multimeter.
Recall that a multimeter can provide the current, voltage, and resistance readings across the components. During an inspection, we usually connect the multimeter probes to the
relays,
capacitors, and
contactors.
All these controls and sensors are connected through the control board and need to be in working condition. If the controls and sensors are not working properly, troubleshooting is needed.
The economizer section consists of dampers, actuators, and controls, and these are to be inspected for better operation of RTU. The TXV is inspected by measuring the refrigerant pressure and by the amp drawn by the compressor. The conditions of TXV’s are, High amp drawn for fully open and less amp drawn for stuck or closed.
The visual inspection for heat exchanger includes checking for any:
Cracks,
Corrosion, and
Vibrations.
The electrical components include a control board, sensors, and controls, and these are to be inspected for better connectivity across the unit.
Question #1: Cleaning of coils includes: (Select all that apply)
Cleaning debris.
Cleaning dust.
Cleaning of coils with water.
Cleaning air.
Scroll down for the answer...
Answer: Cleaning debris.
Cleaning dust.
Cleaning of coils with water.
Cleaning of coil includes:
Cleaning debris,
Cleaning dust, and
Cleaning of coils with water.
Question #2: What are the common things that we should look at while inspecting RTU coils?
Leakage
Pipes damage
Fins damage
All the above
Scroll down for the answer...
Answer: All the above
Recall that evaporator and condenser coils are the two main components of RTU.
Coils inspection includes:
Dust on coils,
Fins damage,
Pipe damage, and
Leakage check.
Question #3:How many types of motor drives are used in RTU?
One
Four
Two
Five
Scroll down for the answer...
Answer: Two
Motor drives are two types of drives:
Belt drive, and
Direct drive.
Question #4: During the motor inspection, we check for: (Select all that apply)
Motor drive.
Dust.
Corrosion.
Overheating.
Scroll down for the answer...
Answer: Corrosion.
Overheating.
During the motor inspection, we check for signs of corrosion and overheating.
Question #5: During the inspection of the belt, we check for:
Cracks
Tightness
Alignment
All the above
Scroll down for the answer...
Answer: All the above
During the belt inspection, we check for
Damage of the belt,
Cracks,
Tightness, and
Belt alignment.
Question #6: In an RTU we need to lubricate which of the following parts? (Select all that apply)
Motor bearings
Filter Drier
Refrigerant piping
Bearing housing
Scroll down for the answer...
Answer: Motor bearings
Bearing housing
We need to lubricate all the bearings in the RTU. These include
Motor bearings,
Motor shaft,
Blower bearings, and
Bearing housing
Question #7: What will the pressure readings in the manifold gauge be compared to the manufacturer’s specified values if there is a leak in the condenser coil?
High
Equal
Low
Zero
Scroll down for the answer...
Answer: Low
If the pressure readings are too low, this means that the coil may have leakage somewhere.
We have to find the leak and repair it. Then we have to fill the refrigerant.
Question #8: P-trap in the drain line prevents ___ from outside entering into the unit.
Water
Rain
Wind
Air
Scroll down for the answer...
Answer: Air
P-trap is a curved pipe attached to the condensate drain line. Drained water is collected at the bottom of the curve of the P-trap. Water in P-trap creates an air seal that prevents air from entering the unit.
Question #9: After pouring distilled vinegar into the drain line for cleaning, then
Immediately flush with water.
Let the solution sit for half an hour.
No need to do anything.
It will clear automatically.
Scroll down for the answer...
Answer: Let the solution sit for half an hour.
Distilled vinegar takes some time to react with the debris and mold inside the drain line. If flush with water immediately after pouring vinegar, it will not clean the drain line.
Question #10: The flame of the burners should be in _______ color.
Red
Blue
Yellow
Orange
Scroll down for the answer...
Answer: Blue
The flame of burners should be in blue. When the flame turns yellow or orange, it means that the burners are dirty.
Question #11: For cleaning the burners, the power supply should be____, and the gas supply should be____ to the RTU.
ON, ON
ON, OFF
OFF, OFF
OFF, ON
Scroll down for the answer...
Answer: OFF, OFF
Before cleaning the burners, we should switch off the power supply and close the gas supply line. The power to the RTU provides electric shock, and gas supply to the furnace may cause a fire hazard.
Question #12: Economizers consist of ____. (Select all that apply)
Dampers
Motors
Filters
Cooling coils
Scroll down for the answer...
Answer: Dampers
Filters
Economizer consist of
Dampers,
Filters,
Sensors, and
A controller.
Question #13: The economizer controller in an RTU regulates the position of ____.
Dampers.
Filters.
Sensors.
Airflow.
Scroll down for the answer...
Answer: Dampers
The economizer controller regulates the damper's position when receiving the signal from the control board and sensors.
Question #14: If the filters are filled with dust, they are _______. (Select all that apply)
Cleaned
Left alone
Replaced
Removed
Scroll down for the answer...
Answer: Cleaned
Replaced
If the filters are filled with dust, they have to be cleaned or replaced.
Question #15: The visual inspection of the heat exchanger includes checking for any:
(Select all that apply)
Cracks
Coils
Loose wires
Vibrations
Scroll down for the answer...
Answer: Cracks,
Vibrations
The visual inspection of the heat exchange includes checking for any:
Cracks,
Corrosion, and
Vibrations.
Question #16: Before inspecting TXV, we need to make sure that;
The unit has been running for one full day.
The unit has been running for at least 5 mins.
The unit has been shut down for at least one full day.
The unit has been recently installed.
Scroll down for the answer...
Answer: The unit has been running for at least 5 mins.
TXV is used to control the amount of refrigerant released to the evaporator section.
Before inspecting TXV, we need to make sure the unit has been running for a minimum of 5 minutes.
Question #17: While inspecting a TXV, if the pressure on the manifold gauge does not change, then the TXV is
Open
Working properly
Having a problem
Closed
Scroll down for the answer...
Answer: Having a problem
TXV is used to control the amount of refrigerant released to the evaporator section.
If there's no change in pressure, that's an indication of a TXV problem, and troubleshooting is needed.
Question #18: The clamp meter reading for the amp drawn by the compressor is high, then the TXV is
Open
Closed
Operating
Stuck
Scroll down for the answer...
Answer: Open
The amp drawn by the compressor depends on TXV operation.
The conditions of TXV’s are
High amp drawn for fully open, and
Less amp drawn for stuck or closed.
Question #19: An electrical component that receives and sends all the signals through a programmed chip is
Relay
Multimeter
Control board
Actuator
Scroll down for the answer...
Answer: Control board
A Control board is an electrical component that receives and sends all the signals through a programmed chip.
Question #20: While inspecting electrical parts we use a _______.
Manifold gauge
Multimeter
Connecter
Anemometer
Scroll down for the answer...
Answer: Multimeter
Electrical parts include relay, capacitor, and switches, which are needed to check for voltage, amperage, and conductivity. We need to check the relay, capacitor, and amperage consumption by using a multimeter