Before you start cleaning your coils, carefully slide your refrigerator away from the wall and unplug the appliance.

Angie's How To Clean Your Refrigerator Coils
If your refrigerator coils are dirty, they go into overdrive, which can lead to larger energy bills and a shorter refrigerator lifespan. A typical fridge uses about 15 percent of a home's total power, and a machine with soiled coils requires about 25 percent more energy to function properly than one with clean coils. That adds up!
3 pros!
There are a few places your condenser coils can be located. If you have an old refrigerator (ten years or older) the coils are probably going to be along the back of the fridge. Newer models often have their coils at the bottom of the refrigerator. Note: There isn't a set-in-stone place for the coils. If you have trouble locating them, check your owner's manual for help finding them.
Once you've figured out where they're located, it's time to get to the coils! If the coils are on the back of the fridge, you should be able to reach them just by moving the refrigerator away from the wall. If they're under the fridge, access your coils by sliding out the condensate pan. Once it's removed, you should be able to see your coils. If there isn't a tray, you can access your coils and just slide them out. Note: This process will be different for every refrigerator. If you run into trouble, consult your owner's manual for more guidance.
If your refrigerator coils look especially dirty, place a piece of cardboard or an old towel on the floor to gather any falling dust.
With a brush attachment, vacuum as much dust and dirt off of your coils as possible. Tip: If your refrigerator fan is visible near your coils, make sure to vacuum it, too. You don't want dirt and dust on your fan blades because it will decrease airflow!
If the vacuum didn't get all of the gunk, a baby wipe is a great way to pick up the remnants. They work well because they're damp, which helps pick up stubborn bits of dust. Tip: If you don't have any baby wipes handy, a damp cloth works, too.
If you're a perfectionist, then there's one more step. Use a paint brush to reach those nooks and crannies you couldn't get to with the baby wipe or cloth. Tip: If a paintbrush isn't doing the trick alone, pair it with some canned air! Spray the air on any stubborn places and then brush away the loosened dust.