Trane TUE080 blowing lukewarm air

[anjp]

My Trane electric ignition gas furnace (TUE080A936K2) is blowing lukewarm air into the home. I noticed that when it kicks on, the air coming out of the vents isn't really hot. The metal ductwork in the basement (that carries the air to the vents) is barely warmer than room temp. But the exhaust chimney gets pretty warm...

The filter is clean, the air returns are from the main floor living room, and all 4 horizontal burners ignite when the furnace kicks on.

Surely the air should be hot hot, not just a pathetic lukewarm, right? Sometimes I actually feel colder when the furnace runs.... thoughts?

[heatseeker]

You could have an improper fan speed or dirty evap coil or leaky ductwork.

[anjp]

Good thoughts. I already tried to check for leaky ductwork. Basically I cranked up the furnace and went around the basement ductwork with a feather to check for leaks. There are a couple small ones that I will seal up later with foil duct tape....but nothing that should drastically change the heat output.

As for the evap coil, I'm not sure that this furnace has one. I did some online research and determined that this is a Trane XB80 model. It doesn't appear to have an evap coil but an aluminized heat exchanger. I suppose it could be dirty but I don't know how to get at it to clean.

Fan speed seems like a likely culprit. The XB80 manual tells me this furnace has 4 fan speeds (but it doesn't have a wiring diagram or say how to adjust). I know it has something to do with the fan wiring on the control board. Right now the jumpers are set - *, *, *, *. I've heard black is high, blue is med, yellow is med/low and red is low. So is my current fan speed at medium? I don't really understand what COOL-H and HEAT-H are. This furnace doesn't provide a/c, only heat.

[heatseeker]

Well no ac and only heat you would not have a coil then. My other thought is that changing the fan speed does not improve the situation, which would be changing the red or yellow from park and exchanging with the one that reads heat, then you might have a gas pressure issue which can be adjusted by a professional. This is not a dyi project.