By October, the air conditioner has finished its real job for the year. Around Chicago that job is only partly about temperature. Summers here are humid. Dew points in the 60s are ordinary, and in a bad stretch they climb into the 70s. The coil spends those afternoons pulling water out of the air, not just dropping the number on the thermostat. That is a longer, wetter runtime than a dry-heat climate, and it is what ages the equipment.
The lake does not cool every house
Lake Michigan still takes the edge off a hot day near the shore. A lake breeze can hold the lakefront in a comfortable range while inland Cook County and Lake County run hotter. Mundelein sits far enough from the water that it often misses that relief. A thermostat setting copied from a high-rise on Lake Shore Drive will not describe a house in the western suburbs. The condenser on that house may have run all afternoon on days when the beach never broke 80°F.
The serious version of this climate is the heat wave of July 12–16, 1995. The National Weather Service counts 583 deaths. O’Hare reached 104°F on July 13, Midway reached 106°F, and the heat index hit 119°F at O’Hare and 125°F at Midway, with dew points in the upper 70s and lower 80s. A lot of those deaths were in homes that could not cool off overnight. Cooling equipment in this region is a safety system in July, which is why it deserves a real look in October rather than a hope that it starts next Memorial Day.
What the season leaves behind
Cottonwood, dust, and a summer of wet coils leave the outdoor unit packed and the drain line film-lined. Restricted airflow makes the compressor run hotter and longer. A drain that is nearly clogged will overflow on the first humid day of the next season, usually into a ceiling or a furnace cabinet. Fall service is a coil cleaning, a drain clearing, an electrical check, and a look at the contactor and capacitor that did the starting work all summer.
Refrigerant is checked when the system is warm enough to give an honest reading, which is one reason the full performance tune-up belongs in spring. Fall is still the right time to find a flat capacitor, a failing fan motor, or a drain that is one month from backing up. Replace the indoor filter before the furnace takes over. The same blower is about to run for the heating season.
How to leave the outdoor unit
Keep the top of the condenser open to the air. A cover made for the unit can shield the sides from leaves and ice. A plastic sheet wrapped over the whole cabinet holds moisture against the fins and gives rodents a sheltered place to nest on the control board. Clear leaves away from the disconnect and the line set so a fall rain does not sit in debris against the electrical cover.
Book spring while the schedule is open
The first hot week of May is when everyone remembers the air conditioner. The useful appointment is earlier, before that week. Zima HVAC can do the fall shutdown and hold a spring tune-up for the same house. Call (847) 323-8314. We are in Mundelein and we cover Lake County. If the heating side needs the same attention, start with winter maintenance before the first hard cold.