What to check before you call, what the symptoms mean, and when to stop and get a technician out.
When an air conditioner runs but does not cool, check five things before calling: the thermostat is set to Cool and below room temperature, the filter is not clogged, the breakers for the furnace and outdoor unit are on, the outdoor unit is actually running, and the condensate drain is not full. Those five account for roughly half of the no-cool calls we see in Ypsilanti every summer.
An AC coil freezes when the evaporator drops below 32°F, which happens for two reasons: not enough warm air moving across it (dirty filter, weak blower, closed registers, dirty coil) or not enough refrigerant in it (a leak). Thaw it by turning cooling off and running the fan for two to three hours, then fix the airflow problem; if it refreezes, the charge needs to be checked.
A failed AC capacitor usually shows up as an outdoor unit that hums but won't start, a condenser fan that only spins if you push it, or a compressor that struggles to start on hot afternoons. It is the single most common air conditioning repair in Southeast Michigan and one of the least expensive, typically fixed on the first visit.
A furnace that will not turn on at all usually comes down to no power reaching the control board or a safety switch holding it off. Check the thermostat batteries and mode, the light-switch-style service switch on the furnace, the breaker, the blower door being fully seated, and the 3-amp fuse on the board. If you smell gas at any point, leave and call DTE at 800-947-5000.
A furnace blows cold air when the blower runs but the burners are not lit or have shut off. The most common reasons are the thermostat fan set to On instead of Auto, a dirty flame sensor dropping the flame after a few seconds, a cracked hot-surface ignitor, a furnace overheating on a clogged filter, or a condensate problem on a high-efficiency unit.
Short cycling is a furnace that starts, runs for a few minutes, shuts off, and restarts shortly after instead of running a full 10 to 20 minute cycle. The usual causes are overheating from restricted airflow tripping the high-limit switch, a dirty flame sensor, a thermostat mounted in a warm spot, or a furnace that is oversized for the house. Each pattern looks slightly different.
The blinking LED on a furnace control board is a fault code: count the flashes, pause, and repeat, then match the count to the legend printed inside the furnace door. Most codes fall into five families: pressure switch, limit switch, ignition failure, flame sensed when it should not be, and polarity or voltage faults. A steady light usually means normal operation.
A standing pilot is a small flame that burns continuously and lights the burners; it is found on furnaces made before the early 1990s. A hot-surface ignitor is a ceramic element that glows to about 2,500°F for 30 seconds only when the furnace calls for heat. Hot-surface ignitors are more efficient and safer but are fragile and typically need replacement every 5 to 15 years.
An AC breaker that trips instantly on startup usually means a short in the compressor, fan motor or wiring. One that trips after several minutes of running points to an overheating compressor from a dirty condenser coil, a failing capacitor or low refrigerant. A breaker that trips only on 90-degree afternoons is usually a weak capacitor or a tired breaker. Reset it once; if it trips again, stop and call.
Water around a furnace comes from one of three places: the AC evaporator coil's drain pan overflowing in summer, a high-efficiency furnace's internal condensate trap or drain line clogging in winter, or a failed condensate pump. Clear the drain line with a wet-dry vacuum at the cleanout, flush the trap, and check that the pump runs. If the water is from the humidifier, it is a different fix.
A thermostat that is blank or unresponsive is usually not getting 24 volts from the furnace. Check the batteries, then the furnace service switch and breaker, the 3-amp fuse on the furnace control board, and the AC float switch. If the screen works but the system never responds, loose wires on the R, W, Y or G terminals or a missing common wire are the next suspects.
On a gas water heater, no hot water usually means the pilot is out, the thermocouple has failed, or the gas control valve has locked out; check the status light and relight per the label. On an electric tank, check the breaker and press the red high-limit reset behind the upper panel. Lukewarm water that runs out fast points to a failed element or broken dip tube.
Call or text and you reach Al, not a call center. Same-day service whenever possible, flat-rate pricing quoted before any work, and the same rate at 2 a.m. as 2 p.m.
