Install the Air Handler / Coil

Mount level, build the drain + P-trap + float switch, and seal the plenum transitions.

Approx. 90 min

Before you start

•Coil/air handler matches the condenser (AHRI) and the metering device (TXV/piston) is correct for the system.
•Return/supply plenum and transitions sized to the unit's airflow (CFM) — undersized ducts starve the coil.
•Drain route planned to an approved termination with the correct pitch; secondary drain or float switch path identified.

Tools & materials

Hanging strap / stand / brackets · Level · PVC pipe, primer, cement, P-trap fittings · Float / overflow switch · Mastic or UL-181 foil tape, sheet-metal screws

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Mount the unit

Set the unit level in its orientation
Mount the air handler level (or pitched toward the drain pan as the maker specifies) on a stand, platform, or hanging straps rated for the weight. A coil that isn't level won't drain and will overflow the pan.
Target: Level (or per-spec pitch toward primary drain)
Leave service access to coil and blower
Keep clearance to pull the coil, change the filter, and service the blower without dismantling duct.

Condensate train

Build a proper P-trap at the primary drain
On a draw-through (most residential) coil the drain is under negative pressure, so it needs a trap deep enough to break the suction or it won't drain. Build the trap, then pitch the line to the termination.
Target: Trap depth per maker (often ≥ 2 in); line pitch ≥ 1/8 in per ft
Install a float / overflow switch
Wire a float switch in the primary drain (and/or secondary pan) into the low-voltage circuit so the system shuts off before a clog floods the space.
⚠ Skipping the float switch is the #1 cause of ceiling/water-damage callbacks. Always install one.
Prime and test the drain
Pour water into the pan and confirm it flows freely to the termination with no leaks at the joints, then prime the trap.

Plenum & transitions

Connect and seal supply/return transitions
Fit the plenum and return transitions, fasten, and seal every joint with mastic or UL-181 tape. Leaky transitions at the unit are the worst place for duct loss.
Target: All joints sealed; transitions sized to rated CFM
Confirm a filter rack with correct size/MERV
Provide an accessible filter slot sized to the unit. An over-restrictive (high-MERV, undersized) filter chokes airflow and freezes the coil.