I first lost my fan speeds 1 and 3 and noticed that my heat smelled as soon as I turn it on. Almost smells like manure but it's a plastic or rubber smell. I found out my resistor was causing the loss of speeds and was hoping that could be the rubber smell as well. I
put in a new resistor and the speeds were fixed but I still have the smell. Its weird too because it's worse as soon as I turn on the heat but eventually seems to get better or go away. But if I turn off the heat and turn back on in a few minutes it smells again. Any ideas?

 

If there is/was any possibility a mouse or other small animal got into your vehicle's ventilating system , that could be what you smell. It is one of the most difficult odors to get rid of. I wound up selling a vehicle because a mother mouse and six babies were found dead under the rear carpet. How they got there was a mystery.
If you can or have a shop chase down the source a lot will depend on the cause and just how the cause and odor can be either reduced or eliminated.
Let's hope this is not the case here.