The right tools can make all the difference
By Mark Parliament
If you are not installing air conditioning units, you’re maintaining these machines, which
means ensuring that you have the right tools for the tasks you’ll be performing for your customers.
Thankfully, tool choices are plentiful for our sector, but there are a number of ”must-have” tools that I turn to, since they are designed for ease of use, comfort and accuracy – and ultimately make the task of installing and maintaining this mechanical equipment much easier.
And please note, while you’ll see a number of my tools in these pages, I am not beholden to any particular brand of product on the tools front, but quality is important, so I tend to stick with some of the better-known brands out there when it comes to equipment that I need to be in
calibration with good precision and accuracy.
Check the flow
Before beginning any maintenance on the air conditioning system, it is important to gain a proper understanding of the total system performance. To properly evaluate the system, the first test to run should be for proper airflow.
Without knowing the proper airflow, we cannot be sure that subsequent readings are accurate, no matter the brand or make of tool we use. After all, garbage in (incorrect readings) equals
garbage out (incorrect troubleshooting).
By using a manometer and static tips after the filter and before the air conditioning coil, you can see the external static pressure that the air mover (furnace or air handler) is being subjected to on the duct system.
By consulting the manufacturer’s blower performance charts, you will be able to see the exact
CFM that is being pushed across the coil. Once you ensure that the system is seeing the proper airflow, you can then move on to a more in-depth diagnosis of the system.
How much heat?
The next step is to calculate the enthalpy. Air conditioners are designed to remove enthalpy
(total heat). Without knowing how much total heat the air conditioning unit is removing,
there is no way to know if the system is doing what it is designed to do.
A digital psychrometer placed in the supply and return gives us both wet bulb and dry bulb
readings from the air stream. By comparing these readings to the psychrometric chart, we
can then be able to surmise the system’s enthalpy. The difference in the readings between
the supply and return of the unit equals the total heat, or enthalpy, that is being removed
from the system.
What’s the amp draw?
Another important factor in understanding the performance of the overall system is to learn the amp draw of the PSC motor (and this is really what a compressor is). This will help you see the amount of work that is truly being performed by the compressor.
By clamping on the common wire with a digital clamp multimeter, we will be able to read the current draw of the compressor and compare it to the current draw of the system.
A compressor that has a very low amp draw is technically not doing any work. This is a possible
indication of a system that is undercharged. On the opposite side of the spectrum, a compressor showing a very high amp draw is a warning that the compression is working hard, and that you may have an overcharged system.
Evening out the airflow
Once we know the correct airflow readings, enthalpy and power consumption, we can get a more complete picture of how the air conditioning unit is performing, and that information can now be used as a starting point to troubleshoot the system.
One of the most common customer complaints is temperature fluctuations throughout the house.
You may, for example, find a change in airflow between seasons. There could be uneven airflow
during the summer months while air circulated perfectly during the colder seasons. Since humid air is heavier than dry air, it is harder to move through the system, and this could cause uneven airflow once the outdoor temperatures rise.
A rotating vane anemometer can be used to read the velocity and air volume and to measure unevenly distributed or fluctuating throws through the cooling coils, extract grilles and registers.
Placing the rotating vane anemometer in the air stream as the air exits the register or grille will measure the airflow and calculate its speed. Using the grille manufacturer’s data, you can then
calculate the throw of the register to ensure it is throwing far enough into the room to get a good enough mixture in the air before stratification.
Hooking up the manifold
One of the final things to do in the diagnostic sequence is to hook up a gauge manifold to
the air conditioning system.
Sadly, this is often one of the first things technicians do, which can create incorrect readings on all subsequent tests. This is because any time a conventional hose and dial type manifold is hooked up, there is a small amount of refrigerant removed from the system. A system that was properly charged at installation could quickly become undercharged from all the hose connections and disconnections completed during a maintenance visit.
The nice thing about hose-less and wireless manifolds is that almost zero refrigerant is lost
during a hookup. Some digital manifolds even come with clamp-on temperature probes and
airflow thermostats that will make a technician’s life very easy when calculating things like
superheat, subcooling and temperature drops across a coil.
Gone are the days where a technician had to do manual calculations to learn what a
system is running for superheat or subcooling. With the proper connection of the clamp-on
temperature probes and insertion of the airflow temperature probes into the ductwork air
stream the digital gauges will make all the calculations for you.