A skilled technician should recognize when the root cause of component failure is related to improper equipment sizing and airflow. At a minimum, there are three tools that service technicians should be familiar with that can help them solve some underlying issues. Those tools are ACCA Manual J, Manual D, and Manual S. 

First, Manual J estimates heating and cooling loads for almost all types of residential buildings. However, Manual J does not tell you which size equipment should go into the house; it only assesses the heat loss and gains on a home. Second, Manual S provides procedures for selecting and sizing residential cooling and heating equipment based on Manual J with the help of the OEM performance data. Finally, Manual D is used to design residential duct systems. 

Before jumping to the conclusion that incorrectly sized, selected, and ducted equipment is the culprit, do your due diligence by thoroughly inspecting the HVACR equipment. 

Manual J 

Let's start with some common complaints by clients that could result from an improper load calculation. Occasionally, you may get a complaint from a customer: "It doesn't feel comfortable to me in here. It feels hot and sticky, even though I have my a/c set to 68°." As you know, this is just one of many complaints that may lead you to conduct a load calculation. Here are other common complaints that lead you to do a Manual J: 

• Clients are complaining of discomfort during design weather days 

• The client is complaining of the inability to control indoor humidity 

• The equipment is short-cycling 

• Repeated parts failures, such as capacitors and compressors. 

It is vital to understand that Manual J is the foundation. It is the first step in diagnosing a potential issue resulting from client complaints about comfort and system performance. 

Manual S 

Next, Manual S is the procedure to ensure the home has the correctly sized equipment that will meet the sensible and latent loads of the house. Manual S emphasizes the importance of using OEM performance data that connects sensible and latent cooling capacity with the loads that affect home comfort. As with incorrect load calculations and incorrect ducting, incorrectly selected equipment has a list of issues that can arise. A home with the wrong HVACR equipment can cause: 

A home with the wrong HVACR equipment can cause: 

• Failure to maintain indoor temperature 

• Insufficient indoor humidity (optimum range is 40-60% RH for health and comfort) 

• Excessive short cycling (leading to wear and tear on the equipment) 

• Unmet sensible and latent loads at design conditions 

Not only can incorrectly sized and selected equipment lead to the above issues, but it can also contribute to health issues for the home's occupants. For health and comfort, 50-60% RH is best. When it comes to Manual S, think of it as fitting the house for 'shoes.' You wouldn't buy shoes that were too big or too small, because that would lead to sores or discomfort; you would buy shoes that fit just right. The same principle applies to selecting the correctly sized HVACR equipment for the home. 

Manual D 

Next are some common issues related to inadequate airflow and poor duct design. For example, when a duct system is not sized to handle the airflow requirement of the system efficiently, your client's equipment may experience: 

• Excessively loud equipment (if your client must turn the TV up when the HVAC comes on, that's called a clue) 

• High static pressure 

• Premature equipment and parts failure 

• Inadequate comfort 

When considering diagnosing and solving ducting and airflow issues, please do not use 'rules of thumb.' There are false ideas that the required CFM equals the floor area multiplied by some magic number or that a particular size duct always delivers a specific CFM. When in doubt, consult Manual D. If you suspect airflow/ducting issues, Manual D should be your next tool to diagnose the problem. 

When it comes to diagnosing, there are so many avenues that must be explored. However, load calculations, equipment selection, and duct designs are the foundation to ensure the home's HVACR equipment will work correctly and efficiently. 

As a technician, you are called to work on the entire system, not an isolated part. All system components depend upon each other. In truth, it is difficult to examine any single aspect of system performance while ignoring the rest of the system. That said, the savvy technician can recognize when the equipment issues will not be resolved by throwing parts or making adjustments. Instead, they will articulate to their client the need to perform a Manual J, Manual D, and Manual S to drill down to the root cause of their issues and provide meaningful and valid remedies, not Band-Aid fixes. 

If you are not comfortable performing the Manual J, D, and S calculations, it is okay to request help and send someone to your client's house to execute these calculations. You may want to consider reading ACCA's 'Bob's House.' 'Bob's House' is a case study that discusses the residential design process from start to finish, using Bob's house as an example. (Although it provides a comprehensive solution for this example, it does not cover every scenario or investigate every possible solution.) 

Your job as a technician is to educate your clients while at the same time being thorough and honest in your diagnosis and recommendations. Be sure to lay out all the facts so that your client can make an informed decision on how they want to proceed to remedy their HVACR system issues.