HVAC guys question - mildew smell when turning on heat

[sh00ter]

Home heat was on for several months and fine. Then yesterday I got hot so I switched over to AC for a day. Then today back to heat and there was a strong moldy smell that came though the vents and I coudl smell it as long as the heat was running (enough to warm house 1 degree). Was there moisture in the ducts from running the AC or something? Seems like it would take longer than a day for mildew to build up? What would you do?

 

[THE JOKER]

I would take a look at the evaporator.

 

[sh00ter]

I would take a look at the evaporator.

Is that typically in the attic or outside? I am thinking the condenser is outside?

 

[THE JOKER]

It’s located inside the interior unit.
If it’s not draining properly, it could mold inside

 

[Bocephus123]

View attachment 335588
It’s located inside the interior unit.
If it’s not draining properly, it could mold inside

they mold when dirty

 

[sh00ter]

Is the canned spray the best way to clean for a do-it-yourselfer?

 

[Bahick71]

You can use the canned sprays, but proceed with caution. Make sure it is not highly acidic.
some say you don't Have to rinse it off, but I would if you can. I have heard of them causing
Serious damage to fins if not rinsed off. I would check your drain and make sure it is not
Plugged up

 

[THE JOKER]

Is the ductwork in the attic or under the floor?

 

[Rustytigwire]

I took my fan blower out and cleaned half a Folgers can of crud from it. The evaporator coil is reasonable. I do need to address it though. Fan runs half as long now.

 

[birdhunter1980]

We call that smell the dirty sock syndrome. Basically it's tiny particles on your evaporator coil that dry out after using your air conditioner and running your furnace. When you use the air conditioner again it gets moist and you smell it for a little bit. Like others have said clean your evaporator coil with some foaming cleaner, this usually takes care of it. Ultraviolet lights have become a great long term solution for this issue. I have a Premier One system on my house and have definitely noticed that the house smells better and my son's allergies are better.