Seasoned technicians experience a time in their careers when experience begins to draw them beyond the numbers on a meter and into a new world of holistic HVAC system problem solving. This change only happens when a technician decides to move beyond the pack and works to excel in their chosen profession. This is a tough yet exciting transition that brings a reward of its own. Let’s look at what it takes to begin this move beyond the rest of the pack.
Measure and Interpret Temperatures
A new technician is diagnosing a system to identify the cause of a customer complaint of a lack of comfort and excessive utility bills. Following an accepted industry practice he measures the temperature drop through the air handler. The equipment entering dry bulb is 74F and the equipment exiting dry bulb is 54F. He subtracts the two temperatures to find an ideal 20F temperature drop across the equipment.
Based on the readings from his temperature meter and a quick calculation, he’s satisfied the equipment and refrigerant circuit is operating perfectly. He reports to his customer that he has found no problems and moves on to his next service call.
Based on the evidence, do you agree or disagree with his diagnosis?
Most experienced technicians will agree that a look beyond the numbers on the temperature meter is needed to solve this customer complaint.
The principle that begs for more investigation is that temperature change through equipment is dependent on the amount of air moving through the equipment. A 20F temperature drop looks good, assuming the fan is moving the proper amount of airflow. However, if the fan is only moving half of its required airflow, a 20F temperature drop indicates a serious issue that needs further investigation.
In this situation, the technician started with temperature, but needed to verify fan CFM first. When low fan airflow was discovered, the logical next step would be to use additional testing procedures to diagnose the problem.
This is a classic example of looking beyond the numbers on the meter to dig to the root of a problem and deliver a complete solution to your customers. It takes extra work, but is the only way to truly solve the problem.
Measure and Solve Air Pressure Problems
Another new technician measures the total external static pressure of a system with a gas furnace. She measures the pressure after the filter and records a pressure of .46-in. w.c. She then reads the pressure before the cooling coil and records a pressure of .45-in. w.c. She adds the two pressures together to find an operating total external static pressure of .91-in. w.c.
The fan is rated at a maximum total external static pressure or .50-in. w.c. The readings on her manometer (pressure meter) and her calculations reveal the fan is operating at a pressure that exceeds the specifications of the equipment manufacturer.
Since she just learned how to measure static pressure and lacks the experience to determine a course of action, she records the static pressure reading on the service ticket and moves on to the next call.
Let’s consider what else should have been added to this call to solve the problem at hand.
When a fan is rated at .50-in. w.c. and total external static pressure is read at .91-in. w.c., it’s clear the equipment is unable to operate as designed and is outside of the published specifications. Airflow will be significantly low and the capacity and efficiency of the system will be drastically reduced.
This calls for the technician to look past the numbers on the meter, and continue to inspect and test the system to identify the solution to the problem. Our job is to make systems work better and provide comfort.
The next step would be to measure the pressure drop over the cooling coil and the filter. These two necessary components of the system are typically the prime pressure obstructions since both are installed in the airstream and create resistance to airflow.
A rule of thumb that can be used to diagnose pressure drops in a gas furnace system is that the coil pressure drop should not exceed more than 40% of the fan rated pressure. (.50-in. x 40% = .20-in. w.c.) Measure the pressure on both sides of the coil and subtract to find the difference in the two pressures. The pressure before the coil is .45-in. w.c. and the pressure after the coil is .12-in. The pressure difference over the coil is .33-in. w.c. The coil pressure drop is more than 150% what rule of thumb indicates and is too restrictive.
An inspection of the coil reveals a ¼-in. blanket of cat hair and other household by-products. It needs to be cleaned. Propose the cleaning to the customer and get the job done right.
The rule of thumb for air filter pressure drops 20% of the fan rated pressure. (.50-in. x 20% = .10-in. w.c) Measure the pressure on both sides of the filter and subtract to find the difference in the two pressures. The pressure after the filter is .46-in. w.c. and the pressure before the filter is .12-in. The pressure difference is .34-in. w.c. The filter pressure drop is three times higher than the rule of thumb indicates it should be. This is a real air stopper.
A discussion with the homeowner uncovers the truth of the matter. The house has been dusty, so the homeowner went to the local big-box store and for $20, bought a “super high efficient air filter.” Now it’s your job to teach the customer the impact of that filter on their comfort and utility bill and offer a solution that will increase their comfort and efficiency. You may also offer additional diagnostic testing to determine the source of the dust in their home.
Does problem solving and solutions require creative thought, investigation and additional testing? Sure they do; that’s the message here. Your decision is to determine what level of technician you want to be and how you will choose to serve your customers.
Do customers want solutions? Sure they do; that’s why they called your company in the first place. Is every customer going to be able to afford the solution? Well, no. But consider it your job to offer the best solution anyway and give them the opportunity to enjoy the benefits of the solution you are able to provide.
Hopefully after reading this article you may have become aware that you stopped short in your testing and diagnosing on some recent jobs. If you did, join the club, nobody is perfect. There has never been a baseball player that batted 1000, but if there was he would still swing and miss from time to time.
Rob “Doc” Falke serves the industry as president of National Comfort Institute an HVAC based training company and membership organization. If you're an HVAC contractor or technician interested in a free test procedure to increase the accuracy of your equipment temperature testing 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.