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Air Handling Unit

Air Handling and Distribution: Routine Maintenance: Chapter 1


Air Handling Unit - Part 1


In this module, we will look at how to inspect, clean, and replace the air filter in an air handling unit (AHU). We’ll also provide an overview of blower maintenance. Skip to quiz!


Introduction


Recall that an air handling unit is a large, rectangular, metal box that’s connected to ductwork. We usually call it an AHU for short.


Recall that an AHU contains an air filter, blower, and heating and cooling components. Let’s look at how to maintain each of these AHU components.


Air filters are usually located at the entrance of the return air in an AHU. When inspecting an air filter, we first need to switch off the AHU. Then, we have to open the respective panel by turning the hand keys or removing screws.


Recall that some air filters are reusable and can be cleaned. We can clean air filters with water. We suggest using a garden hose with a medium pressure water jet to clean reusable air filters.


To clean an air filter, we follow these main steps:

  • Remove the filter and wash it with water,

  • Make sure the filter is dry before replacing it, and

  • Put the filter back.


Recall that we can only clean reusable filters. Other filters must be replaced.


When replacing an air filter, we need to switch off the AHU to open the access panel. Recall that access panels are outer covers of AHUs or any other HVAC system. They can be opened by turning the hand keys or removing screws.


After we locate an air filter, we remove it from the AHU. We’ll need to replace this air filter with a new air filter.



Blowers


Recall that blowers are a type of fan that forces air to move. Commercial AHUs usually have belt-driven blowers.


Blowers are located beside cooling or heating coils to pull or push the air. To locate a blower, we have first to switch off the AHU. Then, we have to open the access panel by turning the hand keys or removing the screws.


We need to inspect V-belts for signs of cracking. If a belt is damaged or looks worn, replace it right away.


After replacing a V-belt, we should assess pulley alignment. Good pulley alignment increases the lifespan and efficiency of an AHU by reducing the wear of pulleys, belts, and bearings.


We can check the tightness of a belt by pushing it down in the middle with a finger. If it goes beyond a half-inch, we should make an adjustment.


Recall that lubrication is the action of applying oil or grease to a motor to minimize friction and allow smooth movement. Grease guns are a device used to apply grease to an electric motor and bearings.


Recall that bearings support loads and also help them to rotate.


Air filters are usually located at the entrance of the return air in an AHU. We can clean an air filter with water. We can only clean reusable filters, while other filters must be replaced.


Blowers are located beside cooling or heating coils to pull or push the air. If a belt is frayed or looks worn, replace it right away. We lubricate blower motors to minimize friction and allow smooth movement.



 

Air Handling Unit - Part 2


In this module, we will look at how to inspect and clean the coil and condensate drain of an AHU. We’ll also look at how to inspect electric heaters. Skip to quiz!


AHU - Coils


Recall that AHUs contain cooling and heating coils. An AHU may contain both heating and cooling coils, or only one of them. Water or refrigerant circulates through these coils.


We need to check for any debris on these coils. We should also check for damaged coil fins, coil leaks, mold growth, and unusual materials on a coil’s surface.


First, we clean coils with a brush. We spray coil cleaner onto the coils and let that sit for ten minutes. We then clean the coils with a water hose in the opposite direction of airflow.


Recall that we have to straighten coil fins with a fin comb if they’re bent. This process is similar to combing our hair. We should straighten the fins slowly, or it could damage the coil.



Condensate Drains


We check drain lines to see whether the water is flowing freely or not. Recall that when air passes through a cooling coil, moisture in the air converts into water. This condensate water is moved out of an AHU using a drain line.


When cleaning drain lines, we first switch off the air handler. We then pour distilled vinegar into a drain line through the opening and let the solution sit for half an hour.


After that, we have to flush the pipe with water to make sure that it is clean and functioning normally. If a drain line is still dirty after this process, we can use a vacuum cleaner to further clean it.


We have to locate the end of a drain line outside a building. We then connect a vacuum hose to the end of the drain line and turn on the vacuum pump. Lastly, we pour water into the drain line to clean it.



Electric Heaters


Recall that we can install electrical heaters in some AHUs in place of heating coils. Electrical heaters serve the same purpose as heating coils but consume more electricity.


First, we have to switch off an AHU and remove the electric heaters from it. We then check the resistance and continuity of the electric heaters with a multimeter. If a multimeter shows the specified resistance value, it means that the electric heaters are working properly.


AHUs may contain both heating and cooling coils, or only one of them. We should check for any debris on these coils. First, we need to clean the coils with a brush. We then clean coils with a water hose from the inside out.


We check drain lines to see whether water is flowing freely or not. Vacuum cleaners are used to pull out clogs from drain lines. We can install electrical heaters in AHUs in place of heating coils. Multimeters are used to inspect electric heaters in an AHU.



 

Question #1: Air filters are usually located at the ________ of the return air in an AHU.

  1. entrance

  2. exit

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Answer: entrance

Air filters are usually located at the entrance of the return air in an AHU.


Question #2: Which liquid can be used to clean an air filter?

  1. Brine

  2. Petrol

  3. Refrigerant

  4. Water

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Answer: Water

Water is used to clean air filters.


Question #3: We have to replace an air filter while the AHU is running.

  1. True

  2. False

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Answer: False

When replacing an air filter, we have to switch off the AHU to open the access panel.


Question #4: We replace the V-belt in an AHU with the _____ size V-belt.

  1. bigger

  2. same

  3. smaller

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Answer: same

We replace the V-belt in an AHU with the same size V-belt.


Question #5: Grease guns are used for _________.

  1. lubricating parts

  2. cutting wires

  3. filling refrigerant

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Answer: lubricating parts

Grease guns are used for lubricating parts.


Question #6: Which of the following is used to support a blower shaft and help it to rotate?

  1. Metering device

  2. Bearing

  3. Grill

  4. Vibration isolator

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Answer: Bearing

Bearings are used to support blower shafts and help them to rotate.


Question #7: Which of the following will happen if we spray a coil with high-pressure water?

  1. Coil fins will bend

  2. The condensate drain will be clogged

  3. The air filter will tear off

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Answer: Coil fins will bend

AHU coil fins will bend if we spray a coil with high-pressure water.


Question #8: How can we stop a rotating blower even after turning off an HVAC system?

  1. Air purifier

  2. Vacuum cleaner

  3. Screwdriver

  4. Bearing

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Answer: Vacuum cleaner

A vacuum cleaner is used to pull out clogs from a drain line.


Question #9: Which of the following instruments is used to inspect electric heaters in an AHU?

  1. Screwdriver

  2. Multimeter

  3. Manifold gauge

  4. Hygrometer

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Answer: Multimeter

Multimeters are used to inspect electric heaters in an AHU.

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