You didn't list model , trane has many . If it is a standard model with an AC fan motor ( var. speed motors are DC now ) you have three speeds in most cases . Most run AC on high and Heat on med . You can play with them to compensate for poor duct design or humidity control . In most cases a relay is mounted on the "board " and either works or does not . Several things could be going on .
Dirty filter could be one - you say no
A dirty fan , if it is covered with dust etc it will not move as much air and use more elec. not doing it .
If your return is insulated on the inside a piece of it may have come lose blocking off some of the air.
A supply lead may also be lose or off causing a drop in static pressure .
A capacitor may be going or gone bad ( they last about 5-7 years now due to restriction on how they can be made.
A fan motor could be going ( most often because the cap. has gone and the motor is trying to run with out it .
If you have duct board or flex duct check then as they both tend to fail after time . I have seen both fall apart over years of use . Our code was changed to only allow milar type flex as the other type ( non foil) would fall apart .
one other thing , it has been colder and for longer this year in some places . When your HP goes into defrost the elec heat comes on and keeps the house from getting cold . If you have lost your strip heat you may feel colder air and mistake it for not getting enough heat .
I will be honest here , the tech should have checked all of this .
