INTRO (0:00 to 0:30)
ON-SCREEN: still photo, flat Phoenix roof at sunrise, single beige package unit, title fades in: C20. Package Units.
VO: In the split system modules, the machine came in two halves connected by a line set. This module, the line set disappears. A package unit is the entire system, compressor, both coils, blower, and the heat source, built into one weatherproof cabinet at the factory, charged, tested, and shipped sealed. In Phoenix, these boxes are everywhere: flat-roof homes, strip malls, mobile home communities. Four and a half minutes, and you will know the whole family.
MAIN (0:30 to 4:15)
[0:30-1:20] One cabinet, no line set
ON-SCREEN: C20-package-unit-cutaway.svg, camera pans across the sections as each is named
VO: Here is a gas/electric pack opened up. Follow the air: return air comes in, passes the filters, crosses the evaporator coil where it gives up its heat, gets pushed by the blower across a gas heat exchanger, and leaves as supply air. At the other end of the cabinet, the compressor and the wraparound condenser coil reject heat to the outdoors, with the condenser fan blowing out the top. Every component you learned in the split modules is here. What is missing is the field-installed line set, and that matters: nobody brazed refrigerant pipe on this job. The factory built and leak-tested the whole circuit. Your connections on a pack are air, power, gas, and water. Not refrigerant.
[1:20-2:10] The three families
ON-SCREEN: C20-three-pack-families.svg, three columns highlight one at a time
VO: Three families, sorted by how they heat. Family one, the gas/electric pack: electric cooling plus a complete gas furnace section, burners, heat exchanger, inducer, and a flue hood right on the cabinet. Everything from the gas heat module applies, including 3.5 inches water column manifold pressure on natural gas. Family two, the heat pump pack: the reversing valve, defrost board, and backup heat strips from the heat pump module, all packaged into one box. Family three, straight cool: cooling only, with optional electric heat strips. Ten-second field ID: gas line and flue hood means gas/electric. Reversing valve and defrost board means heat pump. Neither means straight cool.
[2:10-3:00] The curb and the ducts
ON-SCREEN: C20-curb-and-duct-connections.svg, cross-section with labels appearing: curb, flashing, gasket, supply, return
VO: On a roof, the unit sits on a roof curb: a steel frame anchored to the structure, flashed into the roofing by the roofer, with a foam gasket on its top rail that the unit's weight compresses into a seal. This is a downflow install: supply and return openings face down, and the ducts drop through the roof inside the curb, so the weather never touches conditioned air. Ground-mount packs do it sideways: the unit sits on a pad and ducts run horizontally into the building, the standard setup for mobile and manufactured homes. One retrofit trick to know by name: when a new unit's footprint does not match an old curb, a custom curb adapter bridges them, keeping the existing roof opening. And remember the division of labor: you own the gasket and the ducts. The roofer owns the membrane.
[3:00-3:50] The economizer
ON-SCREEN: C20-economizer-operation.svg, damper positions animate: minimum, free cooling, failed open
VO: Commercial packs usually carry an economizer: linked outdoor and return air dampers that cool the building with outdoor air when outdoor air is cool enough, compressor off. The changeover decision uses either a dry bulb sensor, plain outdoor temperature, or an enthalpy sensor that also weighs humidity. In a dry climate like ours, dry bulb is the right tool. When outdoor air does not qualify, the damper holds a small minimum position anyway, because occupied buildings are required to bring in fresh ventilation air. Now the part that makes you valuable: studies keep finding that around half of installed economizers are broken, and nobody notices, because the unit still cools. Stuck open in summer means the compressor fights 110 degree air the unit invited in, and cooling energy can jump by a third to a half. Stuck closed means no free cooling and no fresh air. Stroke those dampers on every commercial visit.
[3:50-4:15] The crane and the roof
ON-SCREEN: C20-crane-set-safety.svg, exclusion zone highlighted in red
VO: Packs go up by crane, and the lift has rules: the operator owns the crane and the no-go call, exactly one signal person directs it, riggers attach the load at the manufacturer's lifting points, and you own everything else being ready. One rule above all the others: never, ever, under the load. And anyone on site can call the emergency stop.
OUTRO (4:15 to 4:30)
ON-SCREEN: rooftop photo returns, text overlay: Read the article. Take the quiz. Watch Darrel walk a real one in v2.
VO: Read the C20 article, then watch video two, where Darrel walks a live rooftop pack panel by panel. Then get on a roof with us and do it for real. See you up there.