My home has 2 zones each with its own heat pump. We have had all new duct work installed and the units cleaned last summer. before this and now when the heat is running periodically this smell will start coming out of all the vents, this happens for both units...cold air will also be coming out of the vents during this smell. I have researched the internet and many answers, all seemingly wrong, are out there. I have taken the top off both units, vacuumed all debris out(both units are outside, these have the blower units internal to them) and sprayed bleach water on the coils inside...let dry and re-assembled.
directly after I am still getting this smell..the problem is, its not all the time and only few times a day, like the smell from your car ac after you have turned the car off then on again after a few hours.
I am not sure the cycles of a heat pump, apparently it will blow some cold air after heating for some time...then smell.
what is it?