Keeping ants out of your air conditioning unit can be difficult. Removal is critical though. Nesting ants will corrode and eventually destroy your air conditioning unit. By the time ants have nested in a home, or unit, their pheromone trail is strong. Even if you eliminate the ants, you'll need to eliminate that odor trail that tells other ants there's a great homestead in your unit.
Step 1 - Determine Extent of Infestation
If you're seeing ants come and go from your air conditioning unit they may be nesting, or just feeding on something inside the unit. Determine which it is by opening your unit. Exterior air conditioning units have two basic parts—the outdoor unit with the compressor/condenser. This usually sits outside your house. And the indoor unit, which is usually located near your furnace and contains the evaporator part of your air conditioner.
Shut off the electrical power to the unit. Some units simply unplug at the unit, others need to be turned off at the main breaker. Remove any exterior housing or cover to the outdoor unit. Unscrew or unbolt the grill on top of the unit and lift it off. The fan motor and fan may come with it, so be careful not to stretch or pull electrical wires loose. Lift the fan and motor out if they don't come out when you remove the grill. Once this is done you should be able to see inside the unit and determine how serious your ant problem is. If ants are simply feeding on dead insects, ants or debris in the unit, remove the food source and proceed to Step 2.
Step 2 - Kill the Nest
If you have nesting ants inside your unit you can kill them immediately by pouring boiling water over the nest. Or you can use a commercial ant spray to spray the nest. If you want to take a longer, less messy approach, sprinkle borax around and inside the unit. Wait a week to 10 days, then return and clean out the dead ants. If ants aren't nesting, but are simply feeding, remove the food source and kill the remaining ants. Kill them with ant spray, borax (takes a week to 10 days), or boiling water.
Step 3 - Clean out Dead Ants
Once you've killed your ants, you'll need to remove all scent trails, as well as the nest or any debris in the unit. Remove the fan and fan motor and protect them from water spray by placing a plastic trash bag over the motor and any exposed electrical wires. Spray down the inside of the unit, the cooling fins, and all non-electrical parts with your sudsing ammonia and allow it to sit for 15 to 20 minutes. Using your hose and attachment spray from the inside of the unit out to force dust, dirt, debris, ants out of the unit to the outside of the unit. Wash until clean. Replace the fan, fan motor, grill and protective unit and turn your power back on.