A technician shows how to size conductors and ground electrodes, then walks through diagnosing low airflow in HVAC systems by measuring voltage, amp draw, and temperature rise. A 4-ton mobile home unit pulling only 900 CFM developed coil rust from inadequate air and a 60-degree temperature rise.
So if it's 3/0, we got to come back here and find the— back here in the back it shows you the circumference or the total area of 3/0, and you got to add it together. Where's that at? Is 0.3117 square inches, so you double that, so you're dealing with, uh, 0.6 6.2 square inches and you come down here, that's equivalent to a 400. And you come back over here and your ground and electrode sizing, where's that at? 6.6 right here. So if it's copper, if it's 350 through 600, it's a 1/0. 1/0 ground. See how you did that? We added that together and it come up to 400. If you service size of largest service, um, or equivalent area to parallel conduct, equivalent area. Need some luck. We getting there, you're on the right. This weekend, indoor cold froze so bad you can't even see. Um, we have not checked the airflow with the hood. No, I need to check it with it. I told you, I'm gonna tell you what I told Derek. Go ahead and tell Derek. He said airflow with, uh, running it on heat with the heat strips. Yeah, and he did some kind of funky calculation and figured out from there. Um, well, anyway, uh, We did the load, it gave him 25,000. See, that's 2.5 million. Freezing ain't got nothing to do with the load. First thing we're going to do is the airflow. Before you have any more conversation, you need to go over there, turn the heaters on, give me the temperature rise across the unit, and we can figure out the airflow. Remember the calculation we worked with all the guys on? It's been a couple years. Anyway, I need to know the voltage. I need to know the amp draw on the heaters. And then I need to know the temperature rise from inlet to outlet with the heater running. And from that we can determine the airflow and figure out if we got enough air coming across the coil. Yeah, John Wilson had the same problem last week in Mobile, home. He had a 4-ton unit pulling 900 CFM. That was a problem. Unit— well, his biggest problem was the unit was, uh, the coil was rusting out. It was just staying soaked because there's so little air. He had a 15 kW heater with a 60-degree rise across it. 50 kW heater should be somewhere in the 35-degree rise. Think you going to find the same thing over here?
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