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Air Filter Issues & Thermostat Issues


Troubleshooting Air Handling Units: Chapter 1


Air Filter Issues


An air filter in an air handling unit traps the dust particles and sends us clean air. An air handling unit won’t work well even if there are any air filter issues. By the end of this module, you should be able to troubleshoot the air filters issues of an air handling unit. Skip to quiz!


Introduction


All AHUs contain air filters to clean air in a room. If air filters become dirty, the AHU won’t work properly. Dirty air filters can cause the compressor and blower to fail prematurely.


Air Filter Issues


The main problems that can be caused by troubled air filters are:

  • High energy bills,

  • Overheating,

  • Unhealthy air,

  • Poor cooling or heating,

  • Frozen evaporator coils, and

  • Low airflow from vents.


If an air filter becomes clogged, airflow will be reduced through it. This causes the blower motor to work harder to push air through a clogged air filter. So it will consume more energy, thus higher the energy bills. Eventually blower motor can burn out, resulting in overheating or failure of the entire system.


When air filters get clogged, the air handling unit must work harder to compensate for the blockage of the airflow. Often, this causes the blower motor to overheat and leads to system failures.


Recall that an air filter captures the dust particles in the air inside the room. If the air filter is clogged, unfiltered air can bypass the air filter and circulate throughout the home.


Because clogged air filters cause airflow issues, we may experience hot and cold spots in the home. It can be difficult to reach desired indoor temperature levels.


Recall that AHU’s evaporator coils absorb heat from return indoor air. If a clogged air filter is restricting airflow, AHU’s evaporator coils might not receive enough heat from the return air. This can cause the AHU’s evaporator coils to freeze and shut down the air handling unit.


Recall that an air filter traps dust particles as air passes through it. If air filters get clogged, they restrict the airflow through them. We’ve to make sure that air filters get cleaned or replaced according to the manufacturer’s instructions and AHU usage. That could be as frequently as one month.


Cleaning Air Filters


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 AHU 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 putting it, and

  • Put the filter back.



Replacing Air Filters


Recall that we can only clean reusable filters. Other filters must be replaced. Sometimes, even reusable air filters are also torn off or damaged. We’ve to replace these filters.


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



A technician needs to check air filters in an AHU if there are problems like:

  • Overheating,

  • High energy bills,

  • Unhealthy air,

  • Poor cooling or heating,

  • Low airflow from vents, and

  • Frozen evaporator coils.

He needs to consider cleaning or replacing air filters if an AHU has air filter issues.


 

Thermostat Issues


A thermostat of an air handling unit is placed inside the room. We set the desired temperature and control the operation of AHU through the thermostat. An AHU won’t work well if there are any thermostat issues. By the end of this module, you should be able to troubleshoot the thermostat issues of an AHU. Skip to quiz!


Introduction


Recall that thermostats are devices used to set a system to heating or cooling mode, as well as the temperature, blower speed, and many other settings. Air handling units work as per the inputs set by residents on a thermostat.


Temperature sensing bulbs detect and give feedback to a system about room temperature. For example, a user sets the temperature to 65°F on their window unit. The temperature sensing bulb will tell the system to stop cooling when the room temperature reaches close to 65°F.


The main problems be caused by a troubled thermostat are:

  • AHU won’t turn on, and

  • Air won’t reach the desired temperature.

If the AHU does not get control signals from the thermostat, it won’t turn on.


If we notice that indoor temperature is consistently too hot or too cold, there may be a thermostat problem. Some of the most common issues can be:

  • The thermostat is dusty or broken,

  • has loose wiring or battery issues, or

  • is not in an optimal location.


Troubleshooting Sequence


The sequence of steps to troubleshoot a thermostat are:

  • Check the settings,

  • Change the batteries,

  • Inspect the wiring,

  • Clean the thermostat, and

  • Consider the location.


We should not overlook the simplest solution like the settings on the thermostat if the air handling unit is not working. We’ve to check the settings on the thermostat. The thermostat settings can be changed by other members or changed accidentally if the thermostat gets touched when people walk by.


Verify that the thermostat to ‘heat’ or ‘cool’ mode depending on the outside temperature. We also have to verify the temperature setting on the thermostat to check whether it is set to the desired temperature or not. We should try adjusting the temperature setting higher and lower to see if the AHU starts running.


Sometimes the screen of the thermostat goes blank if the batteries are dead. We should try new batteries to see if that resolves the problem.


We should remove the cover of the thermostat to inspect the wiring. We have to look carefully at each wire to ensure it is secure and does not corrode. If there is any issue, we can remove the wires with a screwdriver, strip the sheathing and reattach them to get a secure and uninterrupted connection.


Sometimes thorough thermostat cleaning is all it needs to run AHU smoothly. Mechanical type thermostats’ sensors, contact points, levers, and other parts inside need to be cleaned carefully. We can use a brush or compressed air to clean the debris.


A bad location of the thermostat can affect the working of the AHU. We have to place the thermostat on the wall in a central position away from direct sunlight and drafts. These affect the accuracy of a thermostat and cause the AHU to run incorrectly. We should consider replacing the thermostat if it is in a bad location.



A technician needs to check air filters in an AHU if there are problems like:

  • AHU won’t turn on, and

  • Air won’t reach the desired temperature.

He needs to troubleshoot the thermostat issues and resolve them.


The sequence of steps to troubleshoot a thermostat are:

  • Check the settings,

  • Change the batteries,

  • Inspect the wiring,

  • Clean the thermostat, and

  • Consider the location.


 

Question #1: How does a clogged air filter cause ice formation on evaporator coils?

  1. by adding cooling

  2. by allowing airflow

  3. by restricting airflow

  4. by removing dust

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Answer: by restricting airflow

If a clogged air filter is restricting airflow, AHU’s evaporator coils might not receive enough heat from the return air. This can cause the AHU’s evaporator coils to freeze and shut down the air handling unit.


Question #2: Which of the following problems can be caused by a clogged air filter?

  1. High energy bills

  2. Unhealthy air

  3. Frozen evaporator coils

  4. All of the above

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Answer: All of the above

The main problems that can be caused by troubled air filters are:

  • Overheating,

  • High energy bills,

  • Unhealthy air,

  • Poor cooling or heating,

  • Low airflow from vents, and

  • Frozen evaporator coils.


Question #3: We have to make sure that the air filter is _______ before putting it back into the AHU.

  1. dry

  2. wet

  3. moist

  4. clogged

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Answer: dry

We have to make sure that the air filter is dry before putting it back into the AHU.


Question #4: If reusable air filters media is torn, what should be done?

  1. we have to clean and reuse it

  2. the filter must be replaced

  3. we have to run the AHU without air filters

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Answer: the filter must be replaced

Sometimes, even reusable air filters are also torn off or damaged. We’ve to replace these filters.


Question #5: Which of the following device sends control signals to switch on the AHU?

  1. Multimeter

  2. Compressor

  3. Thermostat

  4. Cooling coil

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Answer: Thermostat

A thermostat sends control signals to switch on the AHU.


Question #6: Which of the following devices are used to tighten the thermostat wires?

  1. Cutting pliers

  2. Wire stripers

  3. Screwdrivers

  4. Adjustable wrenches

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Answer: Screwdrivers

Screwdrivers are used to tighten the thermostat wires.


Question #7: What can we use to clean the debris inside the thermostat?

  1. water

  2. brush

  3. coil cleaner

  4. compressed air

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Answer: brush

compressed air

We can use a brush or compressed air to clean the debris inside the thermostat.


Question #8: We can place the thermostat anywhere in the room since location does not affect the working of AHU connected to it?

  1. True

  2. False

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Answer: False

A bad location of the thermostat can affect the working of the AHU. We have to place the thermostat on the wall in a central position away from direct sunlight and drafts.


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