Running an online HVAC course always lands me the question, “What about the hands-on part?” It’s a very difficult one to answer while on the telephone, but it’s something that is made clear to me all of the time. Let me give you a recent example. We’ll compare the ‘Hands-on’ component to the ‘HVAC Knowledge’ component of this incident


The renters of the home stated, “There was a lot of work done to the air conditioning system (heat pump) before they moved in, in November. It heated “okay” but now it doesn’t cool.”

Upon arrival, the compressor was running and the plug on the defrost control board had been disconnected. After reconnecting the plug to the defrost board and the hooking up gauges, the system started. When it did, I have never heard a system groan, scream, and rattle like this one. My high side gauge immediately rose above 700 psi! Needless to say, I made a mad dash for the disconnect to shut it down.

Since the system had “a lot of work” done on it by another company, I decided it might be a good idea to reclaim all of the refrigerant and weigh the proper charge back in and start fresh. As I watched the reclaim machine do its work, the refrigerant scale started climbing. When all was said and done, I recovered almost 23 lbs. of refrigerant!!!  The system is designed to hold only 7 lbs. 4 oz.

photo 2 (13) photo 3 (11)

After weighing in the proper charge and starting up the system, it began to operate at a normal noise level and somewhat normal pressures and temperatures. Further diagnosis revealed that the indoor TXV had failed. After replacing the TXV, the system operated properly.

Now let’s examine the ‘Hands on’ vs. ‘Knowledge’ components.

Hands on skills required to misdiagnose and grossly overcharge the system:

  • Removal of refrigerant caps from the service ports
  • Hooking up gauges to the service ports
  • Connecting the gauge hoses to the refrigerant tank
  • Overcharging the system with three times more refrigerant than it was designed for – although how this was done, I really don’t know
  • Removing two 5/16″ hex nuts
  • Unplugging the defrost control board

Knowledge skills required to properly diagnose this system:

  • Understanding the pressure-temperature relationship of refrigerants and what they tell you about the system
  • The ability to calculate superheat and subcooling
  • Knowing the refrigeration cycle
  • Understanding the opening /closing forces and operation of a TXV
  • Knowing how to isolate and verify a faulty TXV
  • Following proper charging procedures

The answer is painfully obvious to me, but I will let you be the judge.

The part that really concerns me is, the technician who overcharged the system could be your employee or worse yet the one who works on your air conditioning the next time it fails.

Do you or you technician want to the knowledge to become a great HVAC technician? We can help.

by Ron Walker

Ron Walker
Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.