g/hvac • Posted by u/hvac_hero • 1 months ago

Rooftop package unit changeout on a flat commercial roof — pics from today

Wrapped up a Carrier 48TCA036 to 48TCEA042 changeout today. 3.5-ton to a 3.5-ton, but the old unit was a 1998 and efficiency was in the low 10s. New unit is 15.2 SEER2.

Crane pick was the fun part — the building has no rooftop access for equipment. Had to work with a 40-ton crane from the parking lot and do the pick blind over the parapet. Six inches of clearance on the drop.

Lineset was salvageable (3/8 liquid, 7/8 suction, 65-foot run — within spec for the new unit). Did a triple evacuation to 200 microns. Nitrogen-charged the new unit from the Schrader. Startup temp diff was 22°F. Good install.

💬 4 replies

4 replies

Best New Old Controversial

u/duct_doctor • 1 months ago

Did you have to adapt the curb or was the footprint close enough? Carrier made some dimensional changes around 2010 that make direct curb drops tricky on older builds.

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u/boiler_bill • 1 months ago

What did the electricity bill look like before vs after? SEER 10 to SEER 15 is a meaningful efficiency jump on a commercial building. Did the customer do any kind of energy audit before the changeout?

u/minisplit_mike • 1 months ago

Triple evacuation to 200 microns — that's how it should be done. I still see guys pulling to 500 microns and calling it a day. Good habits.

u/freon_frank • 1 months ago

Six inches of clearance on a blind pick. That's why crane operators get paid what they get paid. Nice install — 22°F temp split on startup is solid. What was your superheat and subcooling on first startup?