FCU and VAV Box & Air Distribution Components

Air Handling and Distribution: Routine Maintenance: Chapter 2

FCU and VAV Box

In this module, we will look at how to inspect and clean FCUs. We’ll also look at the maintenance work needed for VAV boxes. Skip to quiz!

FCUs

Recall that a fan coil unit is a type of AHU that recirculates indoor air only. FCUs provide cooling or heating to a single room only.

The main components of FCUs are:

• Coils,

• Motors,

• Blower fans,

• Air filters, and

• Drain pans.

When cleaning FCUs, we need to turn off the power in order to open the access panel. Then we have to remove the air filter to check for cleanliness. We should clean drain pans, coils, and other accessible spaces within an FCU with a vacuum cleaner.

We must clean blower housings, FCU casings, and other areas with a slightly moist cloth. Moist cloths draw dust particles in, and remove them from an area rather than moving them around. Then, we pour water into the drain pan and check whether the water is flowing freely or not.

We can re-install an old air filter if it’s clean, or replace it with a new air filter. We’ll need to reassemble the access panel of the FCU. Lastly, we turn on the FCU at the thermostat to check that it’s working properly.

VAV Boxes

Recall that VAV boxes are terminal devices, and are installed at the openings of ducts. These regulate the quantity of air entering a room. Let’s look into how to clean a VAV box.

When cleaning a VAV box, we have to switch it off, as well as the AHU connected to it. We have to remove any dust inside a VAV box using a brush or vacuum cleaner. Then, we have to clean it with a dry cloth.

We check for leaks in a VAV box. Air leaks in a VAV box affect the cooling or heating in a room. We also check the tightness of a VAV box’s screws and hanger bolts.

VAV Boxes - Controls

Recall that the main control systems of a VAV box are:

• Thermostats, and

• Damper actuators.

A thermostat connected to a VAV box sends a signal to a damper actuator to change the position of a damper. Let’s look into how we inspect the proper working of these controls.

To inspect a thermostat, we have to check its power connection. Then, we change the batteries of a thermostat if required.

We have to check all of a thermostat’s connections to tighten them. Also, we need to clean inside of it, since dust build up can affect its performance. Dust build up in a thermostat blocks temperature detection, which can cause a thermostat to give inaccurate temperature readings.

Finally, we inspect a thermostat with a multimeter.

When inspecting a thermostat, we should check the voltage between hot, cold, and fan control wires with COM, respectively. A multimeter should read about 24 volts in energized condition, and 0 volts in de-energized condition.

If a multimeter deviates from the noted conditions, it means that a thermostat is not working properly. We have to replace or repair it.

Recall that damper actuators control the opening and closing of a damper. Damper actuators help adjust the airflow in an HVAC system.

We supply line voltage 24V AC and control voltage 0 to 10V DC to actuators. We connect multimeter probes to control voltage terminals and set dials to the ‘V–’ range.

An actuator should be in the closed position at O volts, middle position at 5 volts, and fully open position at 10 volts. If an actuator deviates from the noted conditions, it means that it’s not working properly. We have to replace or repair it.

When cleaning an FCU, we need to turn it off at its thermostat to open the access panel. We should clean drain pans, coils, and other accessible spaces within an FCU with a vacuum cleaner. We can re-install an old air filter if it’s clean, or replace it with a new air filter.

We have to remove any dust inside a VAV box using a brush or vacuum cleaner. We should check the tightness of a VAV box’s screws and hanger bolts. We inspect the performance of thermostats and damper actuators.

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Air Distribution Components

In this module, we will look at how to inspect and clean ductwork. We’ll also look at how to clean air terminal devices. Skip to quiz!

Ductwork

Recall that ductwork are closed pathways made of thin metal sheets. The main types of ductwork are:

• Rigid ductwork - Maintains an exact shape and cannot bend easily.

• Flexible ductwork - Can bend as needed.

Recall the common problems in ductwork that need to be inspected are:

• dents,

• leaks,

• clogs,

• mold, and

• corrosion.

All these problems are inspected visually.

We clean ducts during regular maintenance. Duct cleaning involves cleaning registers, as well as the insides of ducts using a vacuum cleaner. Recall that registers are the grills that we find in the walls at a duct entry.

First, we switch off the HVAC system. Then, we unscrew registers using a screwdriver. We have to clean the insides of ductwork with a brush as far as we can reach. We should collect the loosened dust by inserting a vacuum cleaner hose into the ductwork.

We need to wash all registers with tap water. We have to wash air filters if they are reusable, or replace them. We have to clean any dust that might have come out of the vent and onto the floor. Finally, we screw registers back into place.

Air Terminal Devices

Recall that air terminal devices are where the air is supplied to a room. The main types of air terminal devices used are:

• Grilles, and

• Diffusers.

First, we switch off the HVAC system connected to an air terminal device. Then, we unscrew it and clean it with a brush or vacuum cleaner. We have to clean an air terminal device with water if it’s dirty. We need to place an air terminal device in its original position and screw it in.

Recall that high humidity in air promotes the growth of mold. Mold on air terminal devices can lead to breathing problems. Mold on air terminal devices can’t be cleaned easily. We use detergents or some other chemicals to clean it.

Duct cleaning involves cleaning registers and the insides of ducts using a vacuum cleaner. We have to wash air filters if they are reusable, or replace them. We use detergent or other chemicals to clean mold on air vents.

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Question #1: Which of the following is poured into a drain pan to check whether the drain line is clogged or not?

1. Refrigerant

2. Petrol

3. Water

4. Vinegar

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Answer: Water

Water is poured into a drain pan to check whether a drain line is clogged or not. Vinegar can be poured into a drain line to clean a clog.

Question #2: How can we stop a rotating blower after turning off an HVAC system during routine maintenance?

1. We can stop a blower with our hands

2. We have to wait till it stops rotating

3. We can a use mechanical tool to stop a blower

4. We can insert a screwdriver to stop a blower

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Answer: We have to wait till it stops rotating

We shouldn’t try to stop a rotating blower with our hands or any other mechanical tool. We have to wait until a blower stops rotating.

Question #3: When cleaning a VAV box, we have to switch off the ________, as well as the ______ connected to it.

1. VAV box; AHU

2. VAV box; FCU

3. VAV box; Window AC

4. AHU; FCU

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Answer: VAV box; AHU

When cleaning a VAV box, we have to switch it off, as well as the AHU connected to it.

Question #4: Dust build up in a thermostat blocks ________ detection.

1. refrigerant

2. smell

3. pressure

4. temperature

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Answer: temperature

Dust build up in a thermostat blocks temperature detection.

Question #5: Which of the following affects the performance of a thermostat?

1. Loose wire connections

2. Dead batteries

3. Dust buildup inside the thermostat

4. All the above

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Answer: All the above

Loose wire connections, dead batteries, and dust buildup inside a thermostat can affect its performance.

Question #6: A damper actuator is in the fully open position at ____ of the control voltage.

1. O volts

2. 5 volts

3. 10 volts

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Answer: 10 volts

A damper actuator is in the fully open position at 10 volts of the control voltage.

Question #7: We usually clean the insides of ductwork with a water hose.

1. True

2. False

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Answer: False

We do not clean the insides of ductwork with a water hose. We use a vacuum cleaner or brush to clean ductwork.

Question #8: Mold on air terminal devices can be easily cleaned with _____.

1. dry cloth

2. detergent

3. water

4. brush

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Answer: detergent

Mold on air vents can not be easily cleaned with a dry cloth, water or brush. We use detergents or some other chemicals to clean air terminal devices.