How to Get Your Central Air Ready for a Michigan Summer

Why late April is the deadline

Southeast Michigan summers arrive in a hurry. One week in late May it is 60 degrees with the windows open, and the next week a stalled front parks a 72-degree dew point over the Huron River valley and every AC in Washtenaw County turns on at once. That first humid stretch is when systems that sat idle for eight months reveal what broke over the winter, and it is when every shop's schedule fills. The things below take about an hour of your time, and they are meant to be done before Memorial Day, not after the first night you cannot sleep.

Outside: the condenser

• Take off the cover. If you put anything over the unit in the fall, remove it now. Running a condenser with a cover on will overheat the compressor within minutes.
• Clear the perimeter. Two feet on every side, more on the fan side. Cut back shrubs, move the firewood, rake out the leaves that blew in. Air has to be pulled through the coil and blown out the top; anything in the way raises head pressure and shortens compressor life.
• Look through the top grille. Mouse nests, a dead bird, acorns, a tennis ball. All real finds. If the fan blade is blocked, do not start the unit.
• Rinse the coil. With the power off at the outdoor disconnect, spray the fins gently from the inside out with a garden hose. No pressure washer. If the fins are packed with last year's cottonwood or the gray felt of dryer lint, a proper coil cleaning with chemical foam during a professional tune-up is the better option.
• Check the pad. A condenser that has tilted more than a couple of degrees on frost-heaved soil, which happens on the clay in Van Buren and Sumpter Township, puts stress on the refrigerant lines. We can level it.
• Look at the big copper line. It should be wrapped in black foam from the unit to the wall. Where the foam has rotted away, the line sweats and loses capacity. Hardware stores sell replacement sleeves.
• Confirm the disconnect. The gray box on the wall next to the condenser has a pull-out block or a breaker. Make sure it is in and in the on position. If someone pulled it last fall to winterize, the thermostat will call and nothing will happen outside.

Inside: filter, blower and drain

Install a fresh filter. If you are not sure which one, furnace filter sizes and MERV ratings covers it. Cooling is where a restrictive or dirty filter does its worst, because low airflow across the evaporator coil is what freezes it.

Find the condensate drain. On most furnaces with a coil on top, it is a 3/4-inch PVC line coming out of the coil cabinet, running to a floor drain, a utility sink or a small condensate pump with a reservoir. Pour a cup of water into the drain pan access or the pump reservoir and confirm it empties. Flush the line with a cup of distilled vinegar or a mix of water and a little bleach to kill the algae that grew over winter. If there is a float switch on the drain line, lift it; the system should shut off. A clogged condensate line in June is the reason for water on the floor of a lot of finished basements in Plymouth and Northville, and a floor repair costs far more than a tune-up.

Open every supply register and check the returns are clear. Summer airflow matters even more than winter airflow.

The test run

Wait for an afternoon above 65°F, because refrigerant readings and coil behavior are not meaningful on a cold day, and a system started at 50 degrees outside can actually damage the compressor on some older units. Set the thermostat to cool, 3 to 4 degrees below room temperature, and listen.

Within a minute the indoor blower should start, then you should hear the contactor click outside and the condenser fan and compressor come on. After 15 to 20 minutes, hold a thermometer at a supply register and one at the return grille. A difference of 16 to 22°F is healthy. Go outside: the air coming off the top of the condenser should be noticeably warm, and the big copper line should be cold and sweating.

Call for service if you notice:

• The outdoor fan is not spinning but the unit hums. That is the capacitor, covered in AC capacitor failure signs, and it is a quick fix now and a sweltering emergency in July.
• Air from the vents is cool but not cold, or the split is under 14 degrees.
• The compressor starts, runs briefly and shuts off, or the breaker trips.
• Ice forms on the copper line or the coil after an hour of running.
• Water appears under the furnace.

The Michigan-specific stuff

Cottonwood. From late May through mid-June, cottonwood seed drifts in from the trees along the Huron, Ford Lake, and the older streets in Ypsilanti, Ann Arbor and Belleville, and it mats across condenser coils like insulation. If you live near cottonwoods, plan to rinse the coil again in late June.

Humidity, not just heat. Our summers are about dew point. An air conditioner's job here is as much drying as cooling, and a system that is oversized or running with too much blower speed cools the air without wringing it out. If the house hits 72 but feels clammy, that is a sizing or airflow conversation, covered in lower cooling bill and humidity.

Storms. Summer thunderstorms with quick power blips are hard on compressors. If you lose power while the AC is running, turn the thermostat off and wait five minutes after power returns before turning it back on so the refrigerant pressures equalize.

Age. If the system is from before 2010 it is almost certainly R-22, which is no longer produced and expensive when it can be found. Prepare it for summer, but go into the season knowing that a major repair on an R-22 system is usually a replacement conversation. Repair or replace your air conditioner walks through the math.

What a spring tune-up adds

Everything above is visual and functional. A professional visit adds the measurements: capacitor microfarads against the label, compressor and fan amps, refrigerant charge by superheat or subcooling, static pressure, and a chemical coil cleaning that a hose cannot match. The AC tune-up checklist lists it all. We schedule spring visits for service agreement customers automatically, and for everyone else we strongly suggest booking in April before the schedule fills with no-cool calls.