I completed a diagnostic. While checking through system I found the filter was a little bit dirty, and while trying to inspect the indoor coil I found a definitive crack in the heat exchanger right inside the main limit access to the right on the edge of the dimple. Got system running and found system also low on Freon. Running at a 32° superheat, this means system likely has a refrigerant leak as well. Explained this to the customer and provided them with a replacement estimate. Also advised them that the furnace was not safe to operate and should not be used again. I shutoff gas supply to furnace with customers permission. Customer will talk to realtor and get back to us.
