How Much Refrigerant Does it Take to Make the Fan Blow Harder?

My brother Richard sometimes finds himself helping younger technicians who are stumped and need the help of an experienced professional technician. However, they have to really need help because they know Richard is going to twist their tail a bit in the process.

One day a frustrated tech called and told Richard that he was working on a system with a low suction pressure that was frosting up. He further explained that his new digital gauges were telling him that the superheat was 0, so he added refrigerant. However, no matter how much refrigerant he added, the superheat would not increase.

Richard asked him, “how much refrigerant do you have to add to make the fan blow harder?” There was no response, so Richard asked again, “Tell me, I really don’t know. How much refrigerant does it take to make the fan blow harder?” Finally, the tech responds: “Your question makes no sense! There is no relationship between the amount of refrigerant in the system and how hard the fan blows.” Richard then replies “So why are you trying to fix an airflow problem by adding refrigerant?”

While it is true that an undercharge can cause an air conditioning system to frost, the most common cause of a frosting air conditioning coil is actually low airflow. Always look at airflow issues first when trying to remedy a frosting air conditioning system. Common airflow issues include a dirty air filter, a dirty evaporator coil (caused by dirty air filters), closed registers, and poor ductwork.

One tip-off is superheat.  A system with airflow issues will operate with a low superheat while an undercharged system will operate with a high superheat. Note that if the coil is frozen over it will need to be defrosted before any pressures or temperatures are checked. The ice covering the coil makes its own airflow restriction.

Understanding Relationships is Key

During the quiet times between quarters, our team members will often discuss what students are struggling with, what WE are struggling with, and look for ways to address these issues. The other day we were discussing why many students have such a difficult time learning how to identify the common, start, and run terminals on compressors. A few other problem areas came up – reading diagrams, superheat, subcooling, and system charge compared to superheat and subcooling. Then it struck me what all these things had in common – they are all relationships. You have to compare two or more pieces of information to arrive at a solution. Over my years of teaching, I have noticed that the more abstract a concept is, the more students struggle with it. Identifying components is usually not a problem because that is very concrete, just putting a name with something you can see and touch. Memorizing definitions is also fairly straightforward, even if it is not very exciting. Most students can give us a pretty good definition of superheat. But we lose many of them when they have to actually measure it on a unit. We lose even more when they have to use that measurement, compare it to the manufacturer’s specification, and determine if the charge is correct. I believe if you made a list of all the most important things students should learn to do before they leave you would find the most important skills involve understanding relationships. I don’t know of a sure fire way to teach relationships. I think that people who have a good mechanical aptitude readily see relationships. Students that have difficulty understanding relationships need explicit instructions and lots of practice. Teaching something that is “obvious” to you can be difficult because you have to deconstruct your thinking process so you can explain how you accomplish a task that you do innately. For example, suppose you had to teach someone how to use a screwdriver. Do you know exactly how you hold it? How do you get the screw started? What do you do after turning your wrist a quarter turn so that you can turn the screw some more? I have actually had to teach people how to use a screwdriver and it was one of the most difficult things I have ever taught because I really did not know how to explain it. Admittedly, the screwdriver example is extreme. However, the same type of deconstruction process can be used to explain more analytical processes like measuring superheat. My prescription for helping relationship challenged students is to:

Analyze the task in detail – leave nothing out and assume nothing.

Teach the students the process in explicit detail making sure they understand each step.

Practice, practice, practice!

Patience, patience, patience!

Remember, if all the students could do everything easily on their own they wouldn’t need you.