Two facts for reference
Wet-bulb hours. For the station NOAA's engineering weather data names Jackson/Reynolds, NOAA counts about 261 hours in an average year with the wet-bulb temperature above 73°F, and about 980 hours above 67°F.
Federal minimums. Michigan is in the Department of Energy's North region. There, split-system central air conditioners installed on or after January 1, 2023 must be rated at least 13.4 SEER2, and split-system heat pumps at least 14.3 SEER2 and 7.5 HSPF2.
A list that follows the thermostat
Calendars drift from year to year; the day you flip the thermostat from heat to cool, or back, is easier to remember. This checklist hangs its tasks on those changeover days and on the stretches of running in between. Items marked Tech need a technician with gauges, meters or a combustion analyzer. The rest is owner work. Before opening a panel or touching the outdoor unit, turn the system off at the thermostat and cut power at the furnace switch or the outdoor disconnect.
Habits for any month the system runs hard
- Look at the filter, and swap it when it turns gray. Write the date on the frame in marker.
- Keep supply registers open and return grilles free of rugs, furniture and curtains.
- Listen at start-up. A new rattle, squeal or bang is worth a note with the date.
- Glance at the floor around the furnace or air handler for water.
- Keep paint, solvents and laundry piles away from gas equipment.
Changeover day: heat to cooling
- Before the first warm spell, walk around the outdoor unit and pull out leaves, twigs and anything stored against it.
- With power off, rinse the outdoor coil gently with a garden hose, from the top down. A pressure washer can fold the fins.
- Check that the unit still sits level on its pad and that the foam on the larger copper line is whole.
- Find where the condensate line ends and make sure nothing blocks it. If there is a condensate pump, pour in a little water and watch it cycle.
- Switch to cooling on a mild day and feel the supply air after several minutes of running.
- Tech: refrigerant readings written on the ticket, the capacitor and contactor, electrical connections, and the indoor coil if it shows dust or growth.
The cooling stretch
- Notice which rooms stay warm in the late afternoon, and add them to your notes.
- Watch for frost on the copper lines or the indoor coil. If you see it, shut cooling off, run the fan alone and call.
- Check the pan under the indoor coil for standing water.
- Trim plants back so the outdoor unit has the clearance listed in its installation manual.
Changeover day: cooling to heat
- Run the heat on a cool afternoon, before you depend on it. A brief dusty smell can be normal; a smell of hot plastic or wiring means turn it off and call.
- Test smoke and carbon monoxide alarms, and replace their batteries if they use them.
- Clear leaves from around the outdoor unit if it is a heat pump, and from any intake and exhaust pipes on an outside wall.
- Replace the thermostat batteries if it takes them, and review the heating schedule.
- Tech: for a gas furnace, burners, flame sensor, ignitor, heat exchanger inspection, gas pressure and a combustion test; for a heat pump, the reversing valve, defrost control and backup heat.
The heating stretch
- After a heavy snow, brush the plastic intake and exhaust pipes clear by hand.
- Keep snow from drifting against a heat pump, and let its defrost cycles run their course.
- Note how often the thermostat shows auxiliary or emergency heat, and when.
- Keep setbacks modest on a heat pump if a large swing calls up backup heat when you raise the setting.
After a power outage or a storm
- Wait for power to settle before restarting, and reset the thermostat if it lost its schedule.
- Walk around the outdoor unit for bent fins, a shifted pad or debris in the cabinet.
- If water reached the furnace or air handler, leave it off and have it looked at first.
When to call a technician
- A breaker that trips again after a reset.
- Short bursts of heating or cooling that stop within minutes and start again.
- Water on the floor around the indoor equipment.
- A yellow or flickering burner flame, or soot near the furnace.
- A carbon monoxide alarm. Get everyone outside first, then call for help.
Questions before a replacement
When a repair estimate runs large, ask the same company to price a replacement too, and put these to anyone quoting one:
- Will you run a room-by-room load calculation and give me the report?
- What is the AHRI reference number for the exact indoor and outdoor pairing, so I can look up its rating?
- Are duct testing and sealing in the price, or separate?
- What state license or registration, if any, covers this work, and what is the number?
- Which city permits will the job need, and who pulls them?
- Can you show proof of liability coverage and workers' compensation?
A one-page history
Keep a sheet in a plastic sleeve beside the furnace. List the filter size and each change, every service visit with what the technician found and measured, refrigerant added, parts replaced, and the model and serial numbers of the indoor and outdoor equipment. The next technician starts from your record instead of from scratch, and a warranty claim has dates behind it.