INTRO (0:00 to 0:30)
Cold open on a garden hose running full blast, then a thumb pinching the end. Voiceover: the water did not change. The pump did not change. But what comes out changed completely, because something choked the flow. Every air conditioner you will ever touch is this hose. The refrigerant circuit makes the cold, but the air delivers it, and most of the "broken AC" calls you will run are a pinched hose wearing a refrigerant costume. This video gives you the four numbers that let you prove it: CFM, 400 per ton, static pressure, and the fan table.
ON-SCREEN: AIR IS THE CARGO. REFRIGERANT IS JUST THE TRUCK.
MAIN (0:30 to 4:15)
Beat 1: CFM and the 400 per ton rule (0:30 to 1:20)
Define CFM: cubic feet per minute, the volume of air crossing the indoor coil. Show the C12 400 CFM rule SVG. The baseline: 400 CFM for every ton of cooling. Three tons, 1,200 CFM. Then bend the rule on screen: in humid conditions, slow the air to about 350 per ton so the coil runs colder and wrings out moisture. In a dry climate like ours, run up toward 450 per ton, because there is no moisture to remove and faster air means more sensible cooling. Connect to F3: capacity is 1.08 times CFM times the temperature difference. Cut the airflow and you cut the capacity, no matter how perfect the charge is.
ON-SCREEN: C12-400-cfm-rule.svg, with the 350 / 400 / 450 dial highlighted in sequence
ON-SCREEN: BTU/h = 1.08 x CFM x temp difference
Beat 2: Static pressure, the blood pressure of the system (1:20 to 2:20)
Show the C12 static pressure map SVG. Everything the air touches pushes back: filter, coil, ducts, grilles. That pushback is static pressure, measured in inches of water column, the same tiny unit as gas manifold pressure. Total external static pressure, TESP, is the return side pulling plus the supply side pushing, added together. The design anchor: most residential equipment is built to deliver its rated airflow at 0.5 inches of water column. Then the punchline: real houses routinely measure 0.8 and above, which means a huge share of the systems out there are running strangled. Static is the blood pressure of the system. You do not skip blood pressure because the patient looks fine.
ON-SCREEN: C12-static-pressure-map.svg
ON-SCREEN: Designed for 0.5 in WC. Real houses often 0.8 plus. Above 0.8 = find the restriction
Beat 3: Where the pressure hides: filters and blowers (2:20 to 3:20)
Show the filter ladder SVG. Every filter is a deal: more capture, more pressure. The trap on the ladder is the 1 inch MERV 13 pleat, which can spend most of the 0.5 budget by itself, clean. The honest answer is surface area: a 4 or 5 inch media filter captures at MERV 13 for a fraction of the resistance. Then the blower types SVG: three motors, three personalities. PSC droops hard as static climbs. Constant torque ECM droops less. Constant airflow ECM holds its CFM by spinning faster and eating watts, which means it hides duct problems while it quietly works itself to death. On variable speed systems, static and watt draw tell the truth, because airflow will not.
ON-SCREEN: C12-filter-pressure-drop-ladder.svg, highlight the 1 inch MERV 13 rung in red
ON-SCREEN: C12-blower-types.svg, the three curves drawn in sequence
Beat 4: Turning static into CFM, and the rule that orders every diagnosis (3:20 to 4:15)
Screen capture of a real fan table. The everyday field method: measure TESP, find the blower speed setting, read across to your static, and the table hands you actual CFM. Worked numbers on screen: measured 0.82, table says about 975 CFM on a 3 ton system, 325 per ton, below the 350 floor. That system cannot be judged on refrigerant until the restriction is found. Mention the backup method for furnaces: temperature rise, CFM equals output divided by 1.08 times the rise, covered in the demo video. Close with the law: airflow is verified before refrigerant diagnosis, every time, because low airflow imitates low charge on the gauges. Add refrigerant to a starved system and you now own two problems and a callback.
ON-SCREEN: fan table screen capture, finger-trace from speed tap to 0.8 column
ON-SCREEN: 975 CFM / 3 tons = 325 per ton. STOP. Find the restriction first
ON-SCREEN: AIRFLOW FIRST. REFRIGERANT SECOND.
OUTRO (4:15 to 4:30)
Four ideas: CFM is the cargo, 400 per ton bends with humidity, static is the blood pressure, and the fan table turns pressure into proof. In the next video, Darrel drills the test ports, measures static on a live system, and reads the fan table at the panel. Watch his hands. This is a measurement you will take on every single visit.
ON-SCREEN: Next: measuring static pressure on a real system with Darrel