I have an old TRANE gas furnace unit, model # BLUL20E936BL / serial # 542600480. We have a leak underneath the unit onto the basement floor. We cleaned out the outside drain tube, but that didn't stop the leak. Maybe the drain pan inside the unit is rusted or has trash in it. Where should I look for the drain pan? Any other suggestions on what to check?

Under the A/C coil

OK, I looked up AC coil to see what that is and where it its located. I have found it & noticed that the coil also needs cleaning. So thanks a bunch...

No problem. Since the coil is inside use a cleaner that will not cause any breathing problems since when you turn the unit back off after cleaning some of the vapors/fumes will go into the home.

Perfect information ! Thank you. I was amazed at the mold and "stuff" we have been breathing. I bleached the filter on the coil to kill the mold. My old AC is kicking butt again.

Glad we coud help