I had a Trane XV95 gas furnace installed last July. The installer neglected to do the conversion to propane, and it ran that way for a number of weeks before I convinced him otherwise. During that time frame the unit tripped the high limit switch a number of times and the impeller in the vent blower motor failed (all I'm sure due to the excessive heat being generated since it wasn't configured for propane). The blower motor and gas settings have since been replaced at the very beginning of Dec 2012, and all was well for a while...

I'm now getting this acrid (eye irritating), burning smell throughout my house. I'm cleaning out the house for sale/rent, so the only thing running is the HVAC unit to keep the house moderately warm during the winter - all other appliances have been off for weeks. The smell is everywhere, but seems to be more concentrated in certain locations. I can smell it at the registers and return.

There's a CO detector a couple of feet from the HVAC unit, but that hasn't gone off.

I have my suspicions as to what the problem is, but wanted to get some professionals to weigh in on it before I take action. Any help would be greatly appreciated.