I got a ccall today and as luck would have it (and many layoffs) i was the only tech still on the clock and everyone elses phones were off.
The call was a complaint about smelling gas right after start up.
so up i go to the roof. The unit was a trane. With a huge single burner that reminded me of a mobile home furnace. And right below the gas valve and inducer fan area was a 3/8 copper tube coming out of the heat exchanger.
I've never seen this before. There was a rubber tube stuck on it leading out of the chamber through a hole to fresh air. The tube was dry rotted and crumbling apart and basically venting out (?) into the compartment.
So what was it?
Being that it looked like it needed a tube there i swagged 3/8 copper and fit it over the tube and ran it out side of the unit.