An HVAC service manager's one-line job description could read:
"Be there for your guys when they get stumped."
Discussions with several top service managers revealed one diagnostic method that solves from 50%-70% of service techs long-standing problems and helped reduce the service managers weekly workloads up to 30%.
Before training their service techs in this diagnostic method, each service manager told the same story. They said most technicians solve problems using basic electrical and refrigerant troubleshooting. Training on these basic principles carried the technicians into the field, but their diagnostic skills stopped there.
These service managers were concerned that many techs repeated the same repairs, week in and week out. Few knew how to look deeper and permanently resolve customer issues. The resulting a pattern of call backs and warranty issues left many dissatisfied customers.
However, once the service managers personally learned and practiced airside diagnostics, they discovered the missing link. They realized that for years their diagnostics were incomplete because they assumed the airside was adequate, resulting in misdiagnosis.
Once they realized this, he next step was to train their service techs in the basics of airflow. Their diagnostics became more accurate and their solutions solved problems. Each service manager found the airside to be their prescription for personal stress relief.
Assumptions and Misdiagnosis
Much discussion during training centered around the idea that a vast percentage of the mis- diagnosis, warranty claims, and call backs were caused by low airflow.
One service manager talked about the heating Btu formula. If they assume the required airflow of a 60,000 input, 54,000 output, 90% AFUE gas furnace is 900 cfm, and the temperature change through the equipment is 55.5 ᵒF, the equipment works perfectly; 900 cfm x 55.5 ᵒF x 1.08 = 54,000 Btu.
However, if airflow is measured on the same system and found to be 30% low, the diagnosis would be completely different. 600 cfm x 55.5ᵒF x 1.08 = 36,000 Btu. He explained this was the root cause of his service department problems. Once he added the airside to his company’s diagnostics, life got better.
When attempting to diagnose with one essential piece of data is missing, the diagnosis and the recommended solution often fail to produce the promised solution.
Once these service managers got their techs properly trained to assess airflow in the field, they reported help calls declined, warranty costs dropped, and call backs significantly declined.
Because the airside of a system is invisible, unless it is measured and diagnosed, it is easy to assume the airside is performing as it should.
Now let's take a look at how airflow assumptions lead to misdiagnosis in refrigerant and temperature diagnostics.
Refrigerant pressures and temperatures are affected by airflow through the system far more than most professionals will acknowledge. Over the last 10-years, most refrigeration standards or credible industry practice has added airflow verification as a starting point for refrigerant testing and diagnostics. Yet, much of the industry hasn’t caught on yet.
Without airside verification, repair recommendations will normally miss the mark. If an unneeded or incorrect repair is done, system performance deteriorates even further, increasing the need for more complex diagnostics and repairs. Year after year, the downward spiral continues, and your poor customer pays the price.
The failure reported in the recently released HVAC 4 study claims that Utility Refrigerant Charge and Adjustment (RCA) energy savings programs fail to produce the savings promised to ratepayers.
The primary reason for this revelation: the programs assume airflow is correct, when it isn’t. The principles of these programs are correct, but they left out the airflow measurement requirement. Utilities don’t believe HVAC technicians can assess equipment airflow in the field.
This is an example of diagnostics focusing on a single system component, excluding other related testing, that has led to substandard results for decades.
The most commonly used heating diagnostic test on the street is temperature rise over the equipment. Temperature is measured where air enters and exits the equipment. They are subtracted and compared to specifications or industry traditions. If temperature rise falls within specifications, the equipment is considered "good to go."
This test also assumes system airflow is at design. However, since airflow is often found 20% to 40%, low, temperature rise is misleading.
When airflow is 30% below specifications, temperature rise through the equipment will increase.
A very typical diagnosis is an "acceptable" temperature rise over the equipment of, say 40ᵒF, leaving the technician thinking all is well. If airflow were verified to be 30% less than specification, the diagnosis would obviously show the equipment performing almost 30% below specification.
Temperature diagnostics is always tied to the amount of air through the equipment -- period.
How Can I Add Airside Diagnostics to Service Calls?
Assessing the airside of the system on a service call takes about 5 minutes. This quick test requires you to measure the system’s total external static pressure and check the fan speed setting.
With these two pieces of data, you can plot fan airflow on the equipment fan table, which is usually available online. With this added information, your diagnostic accuracy increases, and your ability to permanently solve problems skyrockets.
In fact, your friends at NCI have created a new free app that can be downloaded to your smartphone that will estimate fan airflow for systems five tons or smaller. The app also provides graphics you can show to customers to help them understand the state of their system. Simply go to https://airmaxxlite.com/ and download to your Apple or Android smartphone.
Rob “Doc” Falke serves the industry as president of National Comfort Institute, Inc., an HVAC-based training company and membership organization. If you're an HVAC contractor or technician interested in a free test procedure describing how to plot fan airflow, contact Doc at [email protected] or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles, and downloads.