HVAC in Indianapolis spans a real winter and a humid summer with a short gap between. Older basements often hold the furnace beside the water heater, with weak upstairs ducts. Newer attics hold ducts that bake. A few blocks still heat with radiators. Say no-heat or no-cooling before the brand. One cold room over a garage is not a whole-system failure.
Filters, a collapsed return, and a buried outdoor unit imitate bigger failures. Snow here melts and refreezes around the condenser instead of sitting all season, and ice still blocks the fan. Salt from the street drifts into side yards. Ask what was ruled out. A flue that has not been looked at is not a thermostat story. Heavy upstairs air while the thermostat is satisfied shows up the first real summer week.
Replace for this house, not for the label on the old box. Attic ducts and tired windows change the load. New outdoor equipment on an old coil is not a matched pair. People delay in the short mild weeks and then call on the worst night. Say forced air or radiators. A tight basement still has to give combustion equipment air and a sound flue.
A clogged condensate line can stain a ceiling and imitate a roof leak. Upstairs window units drip into plaster and become a wall problem. Clear ice from the outdoor unit only if you can do it safely. Do not open gas compartments. If a freeze may turn into a claim, say so when you describe the equipment.
Say old basement system or attic ducts, and which floor fails. Have the model plate only if it is easy. Salt slush refreezing around the outdoor unit is a winter habit here, not a fluke. The weather will swing back to the other extreme before you are ready. Call the number on this page.