TM99A thermometer, courtesy of Cooper-Atkins Corp.

If I were to ask you, “Which instrument or tool best typifies the HVACR industry?” what would you say? I’m sure that the answer most would give is a refrigeration manifold and gages. But is ours a business of pressures or temperatures? It’s really a business of temperatures, so perhaps an accurate electronic thermometer that reads in 10ths of a degree would be far more suitable for our business - but I won’t hold my breath until that happens.

Yet, despite the fact that refrigerant pressures are only occasionally important, gages and pressure readings remain the staple of most service technicians, and many don’t carry or use accurate thermometers.

What is the purpose of refrigerant gages? Manifolds must be used when evacuating and charging, but the gages can give us an idea of system compression ratio (which few people understand); they can provide some idea of internal saturated refrigerant temperatures (but they aren’t very accurate); and they can show the pressure drop across refrigerant lines and filter-driers. And that’s it!

On the other hand, accurate digital thermometers can do almost all of the above, plus check system efficiency and indicate a proper system charge, and they don’t contaminate the refrigerant lines.

Some time ago, I was asked by a top local commercial/institutional/industrial A/C contracting company to put on a series of training classes for their service technicians. And during the class on performing preventive (not preventative) maintenance, when I suggested that the technicians not connect their gages but use thermometers instead, the service manager stopped me and said, “I’ll fire any man here who doesn’t hook up his gages when pulling a PM!”

I explained to him that most refrigerant gages are not that accurate. They carry all sorts of contaminants and after the technician leaves, there is a greater possibility of refrigerant leaks. Also, since all the necessary refrigerant and airflow checks are more accurately performed with a good electronic thermometer, the customer is better served by not hooking up the gages.

Well, he was an old-school service technician, and all these modern ideas didn’t sit well with him. However, the entire refrigeration process in all systems is based on just three things: superheat, sub-cooling, and saturation (which are not pressures but temperatures).

And despite what I wrote in an earlier column about not using wet-bulb readings of the discharge and return air flows to charge air conditioners, they are invaluable when diagnosing system problems. Using the total-heat formula, an air conditioner will show a 6.67-Btu wet-bulb temperature drop (as plotted on a psychometric chart) when the system is working properly and the airflow is exactly at 400-cfm/ton. And this takes all the guesswork out of whether or not a system is working at peak efficiency.

So, what am I suggesting here? That you carry and promote a good line of inexpensive, easy-to-use and accurate electronic thermometers and that you suggest to technicians that they should abandon their old, inaccurate stick thermometers. Also, providing a class to emphasize temperature readings over inaccurate, contaminating gage readings would be a good idea - for the betterment of our industry.