In this short instructional video, HVAC field technician Mike Plezia explains the 80/20 (often closer to 90/10) rule that governs the time spent charging a system. He draws a parallel between charging a cell‑phone battery and charging refrigerant into a condenser, arguing that most of the charging time is consumed by the final portion of the charge because the pressure (or voltage) differential that drives flow diminishes as the target approaches full charge. Mike describes how electrical energy always moves toward lower potential (ground) and how refrigerant flow follows the same principle, making the last pound of refrigerant hardest to add. He gives concrete examples, such as transitioning from R‑22 to MO‑99 and recharging a 5‑pound system, illustrating why the first bulk of refrigerant enters quickly while the final amount requires more effort. The video ends with an invitation for viewers to suggest future topics for new and aspiring technicians.
Chapters
Hey, what's going on everybody? It's Mike again. Just thought I'd make a quick video for you newer techs or aspiring techs out there in the field. I hope you're having a wonderful day and a great fall season. I know in the Midwest here in Illinois, it's been a little slow. Not much work going on, but we're staying steady with the maintenances. So one thing I wanted to ask you guys and discuss today is the 80/20 rule. I don't know if anyone ever told you, 80% of the time you spend charging a system is going to be devoted to the last 20% of the charge. And actually, if you think about it, the same holds true for batteries. You know, the first 80% of your cell phone takes no time. In fact, you put it on the charger, it seems like you blink an eye, it's 80% charged. But that last 20% always, you know, takes a lot longer. Why is that? So the reason is Pressure differential in both electrical flow and in, uh, just the pressure with your refrigerants. Um, the lower— the higher, excuse me, the pressure in the receiving unit, um, or the battery in the case of your cell phone, or in the condensing unit in the case of this air conditioner, um, the longer the time is going to take to actually complete that charge. Reason is, think about Uh, think about ground. When your circuit is energized, any old circuit, whether it be a light switch, a light bulb, your condensing unit, furnace, whatever have you, um, you know, electricity always, always drawn toward ground, because ground is, um, the lowest concentration of energy. So, energy always wants to travel from high To low. So, in order to equalize. So, energy, electricity is always drawn to ground. Well, in the case of a battery, there isn't a true ground, um, as in it's not coming into contact with the actual earth, but, um, you do have an absence, or an empty space, or a vacuum of energy that's quickly drawing all the abundant energy in from the source in order to be stored in the battery. As the battery fills, there's less of a pressure differential drawing energy into the battery. So that way the flow of electrons actually slows down until you get to the last 90-95%. I always notice my cell phone, it takes like 3 years to go from 95% to 100%, but it took maybe a half hour to go from 5% to 80%. Um, the same holds true with your condensing unit. You know, if you're charging— A condenser, you might notice that at first, you know, like especially if you're doing a, uh, uh, transition, say from, uh, you know, R-22 to, to MO-99, or something like that, um, or just recharging a system after, you know, you had to completely remove the charge, um, that first, you know, few minutes, boy, you, you know, say it's a 5-pound system, that first 4 pounds flows in easy, but man, you might, you know, you really need to almost fight to get that last pound in. And that's because the differential between the refrigerant in your jug, in your jug, and the refrigerant in the condenser is so much closer now than when you began. So, the 80/20 rule is absolutely correct. 80% of the time charging a device, i.e., transferring energy from a source to, you know, a different area of low pressure, is going to be spent with the last 20% of the charge. And I would say that number might even be closer to a 90/10 rule. But just a thought, something I wanted to get out there for you guys to chew on. Hey, if you have any other suggestions of topics, ideas, especially for the new and aspiring technicians in the trade, feel free to shoot me a message. And definitely appreciate you guys' support. Have a great day and stay safe out there, guys.
