How to winterize an AC unit (and when not to)

First: is it an AC or a heat pump?

A central air conditioner and a heat pump look almost the same outside. The difference matters: a heat pump runs all winter to heat the house.

• If the outdoor unit runs when the heat is on, it is a heat pump.
• If your thermostat has “Em heat”, “Aux heat” or “Emergency” settings, it is very likely a heat pump.
• The label on the outdoor unit usually names the type; the model number can be looked up with the maker.

Have a heat pump? Skip the cover and the power shutoff, and follow our heat pump maintenance guide instead.

Clear debris from the outdoor unit

Fall leaves, seeds and grass clippings collect in and around the outdoor condenser. The DOE notes that outdoor coils can get very dirty in dusty areas or where there is foliage nearby.

• Pick leaves and twigs out of the top grille and from around the base by hand.
• Trim shrubs back so air can move freely in spring; keep about two feet clear on every side.
• With the power off, you can rinse the fins gently with a garden hose. Skip pressure washers and stiff brushes – the fins bend easily.

Turn off power at the disconnect (AC only)

Next to the outdoor unit is a disconnect box with a pull-out block, switch or breaker. Turning it off for winter keeps the AC from starting on a warm spell or by mistake when the outdoor air is too cold for cooling.

One caution: some air conditioners have a crankcase heater that keeps the compressor oil warm while the unit has power. Check your owner’s manual. Some makers ask you to restore power well ahead of the first cooling day so the heater can warm the compressor before it starts. When in doubt, leave the power on and simply keep the thermostat off cooling.

To cover or not to cover

Outdoor units are built to sit outside in rain and snow, so a cover is optional. Opinions differ, and both sides have a point:

• A top-only cover – a breathable panel or mesh over the top grille – keeps leaves, seeds and ice from falling in while leaving the sides open so moisture can escape.
• A full wrap that seals the sides can trap moisture and condensation inside, which can encourage rust and corrosion, and gives mice and other animals a sheltered place to nest and chew wiring.

The safe rule: follow the maker’s guidance for your model. If you use a cover, make it breathable, top-only, and secured so it cannot blow off. Remove it before the system runs again. Never cover a heat pump.

Snow, ice and roof drips

• Brush heavy snow off the top with a broom after storms. Do not chip ice with a shovel or other tool – a punctured coil means a refrigerant leak.
• Keep gutters above the unit clear so water does not drip and freeze on it.
• Do not pile shoveled or plowed snow against the unit.

Refrigerant lines and wiring

Look at the two copper lines that run from the outdoor unit into the house. The larger one should have foam insulation; if it is cracked or missing, ask about replacing it at the spring service. Check that the wiring conduit is attached and that no animals have nested around the base. Do not open the electrical panels on the unit.

Outdoor faucets and hoses

While you are outside, deal with the water lines. The American Red Cross advises removing, draining and storing outdoor hoses, and closing the inside valves that supply outdoor hose bibs. Drain pool and sprinkler supply lines following the maker’s or installer’s directions. More in our guide on how to prevent frozen pipes.

Spring start-up

Before the first warm day: remove any cover, clear debris, restore power at the disconnect (following any wait time in your manual), and test cooling on a mild day. Our AC maintenance checklist covers the rest, and the HVAC maintenance checklist lays out the year.

Sources

• U.S. Department of Energy, Energy Saver: Maintaining Your Air Conditioner (checked October 2026)
• American Red Cross: Preventing & Thawing Frozen Pipes (checked October 2026)