Outdoor Unit Placement, Mounting, and Defrost/Drainage
This domain tests outdoor unit location, clearances, mounting, vibration control, and defrost water management. Expect questions on recirculation, snow and ice, service access, and how placement affects defrost and drainage.
Core rules and concepts
- Follow manufacturer clearances, commonly 12–24 inches at sides, 18 inches for service access, and 60 inches above the fan. Two units need adequate spacing to avoid recirculation.
- Avoid recessed walls, deck enclosures, dryer vents, and prevailing-wind pockets that cause discharge air to recirculate.
- Raise the unit above the expected snow line and keep the drain path clear. In cold climates, a elevated stand or wall bracket is common.
- Mount on a level, stable pad or bracket with vibration isolation. Coastal installations need corrosion-resistant fasteners and coils.
- Defrost water must drain away from the foundation and not pool under the unit. Heat tape or a heated drain pan may be needed where freezing occurs.
- Maintain access for service panels, electrical disconnects, and coil cleaning.
Worked example
A unit is installed 10 inches from a solid wall because the space is tight. The manufacturer requires 24 inches at that side. Discharge air will recirculate, raising head pressure and causing repeated defrost or high-pressure trips. The correct response is to relocate the unit or use a bracket that meets the clearance, not to trim the fan blade or remove the service panel. Verify the new location also meets top clearance and drain slope.
Traps that cost marks
Installing under a deck or in a wall alcove; blocking service access; letting defrost water drain onto a walkway and freeze; placing the unit below snow level; and ignoring wind-driven recirculation.