Trane Bvent Gas Furnace smells up the whole house. Even when the furnace is off and the AC turns on, the house smells like the basement.?

I have a 3 year old Trane Xr80 BVENT Furnace, uses inside air for combustion. Air condtioner obviously doesn't use any pilot lights. It's in a old basement. When I turn either on the house stinks like the basement. If I blow a match out the smoke sucks inside the air intake and smells the house like smoke. I turned the furnace on and put a CO detector in front of the vents and they didn't detect any gas, so I don't think the heat exchanger is broke, could it be?

I checked all the vents with smoke and none draw smoke in. I also taped and sealed them anyway. My previous furnace never smelled the house and I didn't have AC before. It seems this draws everything in and stinks up the house.

I saw info talking about AC hooked up to a furnace with a condensation pump that molds up and draws air through mold. Mine doesn't have a pump. It has the AC tubing going strait across the ceiling into the top exhaust duct work, then a piece of fountain tubing running across the floor to a drain, should it go this way?

My yearly maintenance, say "Oh your basement is too dirty" When cleaned even if the basement smells, the furnace shouldn't be drawing a smell & sending it through the house. The same yearly maintenance man will be here tomorrow. He put it in 3 years ago, so he will say "Oh it's good, nothing wrong" So any ideas of what issues to tell him, would be appreciated. If I light a match the smoke sucks in. The filter is brand new. I taped over it and any hole I could. Still smells bad.