I have a Goodman central heating and air unit and just when the temperature starts dipping into the 30s this thing is failing. Air is blowing through vents, but it is NOT warming up in my home and the auxiliary is on. This unit is just five years old. Argh.. Any thoughts on what could be wrong with it?

Would help to know if its electric or gas furnace

I agree with wmproop. Auxiliary makes me think heat pump with electric backup. Need to know.

It's an electric central heat and air unit. Goodman Central Air & Heat Pump Model #PHKJ042-1C with serial #0407637181 does not warm house. Vents are blowing air, but auxiliary cuts on and Hunter thermostat #42122 -- which was replaced during the summer for ac issues. It is a two-stage pump with NO heating kit. Let me know if this helps? Thanks for your assistance!

I mean two-stage thermostat...