What causes a musty odor when heat is turned on in a 1998 explorer?

Answer 1

IT IS USUALLY CONDENSATION FROM YOUR AIR CONDITIONING, IT GROWS MOLD AND BACTERIA. WHICH WILL SIT THERE ALL SUMMER AND WINTER. HOWEVER IN THE WINTER WHEN YOU BLOW YOUR HEAT IT WARMS UP THE BACTERIA AND MOLD. THERE IS A PRODUCT CALLED FRIGI-FRESH MADE BY B.G. WHAT YO NEED TO DO ONCE YOU GET FRIGI-FRESH IS SPRAY IT IN THE FRESH AIR INTAKE. USUALLY LOCATED BETWEEN THE WINDSHIELD AND HOOD. WITH YOUR AC ON FULL BLAST. SPRAY THE WHOLE CAN. THIS SHOULD FIX YOU UP

Answer 2

A musty odor when the heat is turned on in a 1998 Explorer could be caused by mold or mildew growth in the HVAC system. This typically occurs when condensation builds up in the system and creates a damp environment for mold to thrive. It is recommended to have the system inspected and cleaned to remove any mold or mildew buildup.