Interior mold ordor

I have a 2004 Dodge Dakota I bought used. Every time I turn the heater / defroster on I smell a mold odor. I am very alergic to mold and develope a nasty sinus headache and runny nose very quickly.

Question: is their a filter I can change at the air intake point & ( where is it )

could I mist a bleach water mix at the intake area? Hoping that the bleaqch gets sucked up and kills the mold where ever it

is. I am desperate. I thought I heard some where on a show ( maybe yours ) a caller having this same problem but I only caught the tail end of the conversation.

please help, its too cold now to go with out heat. Thank you.