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How often should you winterize your air conditioner?

Updated

Short answer

Winterize the air conditioner once a year, after the last use in fall. The job is small: clear out what's collected in the outdoor unit over summer, shut off the power so it can't start in a warm spell, and protect the top from what falls on it over winter. It takes 15 to 30 minutes and costs $0 to $40, depending on whether you buy a cover. If your outdoor unit is a heat pump, skip the cover entirely, because it runs all winter.

Why it matters

The outdoor unit sits exposed from the last cool night in fall to the first hot day in spring. Leaves blow into it and settle on the bottom pan, where they hold water against the metal. Ice builds up on the fan blades and the coil. Mice and squirrels find the sheltered box an inviting place to spend the winter, and they chew on wiring while they're there.

None of that shows until spring, when you turn the system on and the fan is bent, the pan has rusted through, or the wiring is damaged. Debris that rotted in the unit all winter also blocks the fins you'd otherwise have cleaned before cooling season. A few minutes in fall spares you the surprise, and the repair bill, in spring.

When to do it more often

Winterizing happens once, after the last use. The thing to watch for is doing it too early. A warm week in October can bring the cooling back on, and if the unit is covered, the fan will pull the cover into the blades or run with no airflow. Wait until you're sure cooling season is over, and if a late warm spell comes, take the cover off before anyone touches the thermostat.

The one case where the whole job changes is a heat pump. It looks like an air conditioner but it heats the house in winter, so it must stay uncovered and powered. For a heat pump, winterizing means only clearing debris and keeping snow from piling against it.

What you need

  • A garden hose, to rinse out summer's grime before it sits all winter
  • A top cover or a piece of plywood, sized to the unit

Steps at a glance

  1. Run the AC on a mild day to be sure it still works, so a problem gets fixed now rather than found in spring.
  2. Shut off the power at the disconnect box beside the unit.
  3. Pull out leaves, twigs and grass from inside and around the unit, and rinse the fins with the hose.
  4. Let the unit dry completely.
  5. Lay a cover or a board over the top only, leaving the sides open to breathe, and weigh it down.
  6. Keep the power off until spring, and put a reminder on the thermostat so nobody runs the AC with the cover on.

You're done when the unit is dry, the top is covered, the sides are open, and the disconnect is off.

Signs it's overdue

  • Leaves and debris inside the unit when you look through the top grille.
  • Ice built up on the fan after the first freeze.
  • Animal nests, droppings or chewed insulation inside the unit in spring.

DIY or pro

This is an easy job for anyone who can pull the disconnect and lift a board. Nobody sells winterizing as a separate service, so there's no professional price to compare. A technician doing a fall furnace tune-up will often cover the AC if you ask, but it's quicker to do it yourself the weekend after the last warm day.

Whatever you do, cover only the top. A full wrap that seals the sides traps moisture inside, which rusts the coil and invites mice looking for a dry, dark home. A board held down with a brick does the job better than a snug fitted cover.

Safety

  • Electricity: pull the disconnect before you reach into the unit to clear debris. The fan can start without warning if the thermostat calls for cooling, and a running blade will take off a finger. Leave the power off through winter and restore it in spring before the first use.

FAQ

Should you cover your air conditioner in winter?

Cover only the top, to keep out leaves and ice. Leave the sides open so moisture can escape. A full wrap does more harm than good.

Can you run the AC with the cover on?

No. The fan pulls the cover into the blades, or runs with no airflow and overheats. Take the cover off before the first warm day.

Do I need to winterize a heat pump?

No cover and no power shutoff, because it runs all winter. Clear debris around it and keep snow and ice from piling against the sides.

Is it bad to leave an air conditioner uncovered all winter?

The unit is built to live outside, so an uncovered one will usually be fine. The cover protects the fan and coil from ice and heavy debris, and it keeps the unit cleaner for spring.