Start from the symptom. Read the full diagnostic walkthrough.
Cold Air from FurnaceFurnace runs but supply air is coolShort CyclingRuns briefly, shuts off, repeatsFurnace Won't StartNo ignition, no blower, nothing happeningLeaking WaterWater on the floor near the furnaceAC Not CoolingBlower runs, condenser hums, air is warmStrange or Dangerous NoiseBoom, scrape, scream, or rumble from the unit
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