How to Reduce that Foul HVAC Odor

How to Reduce that Foul HVAC Odor

Is there a bad smell coming from your HVAC vents? It’s nothing new, but unfortunately there’s no cure that completely eliminates the problem. However, there are some easy and inexpensive things you can do to make the odor less offensive.

The source of the foul odor: moldy evap core

The cause is microbiological growth (mold) in your truck’s HVAC evaporator case and ducting, and the odor occurs when you use the air conditioning system on warm or hot days. The HVAC system naturally produces condensation as a byproduct of running the A/C. The problem starts when you turn off the vehicle and the ambient temperature and the radiant heat from the engine make a perfect petri dish for growing mold. The mold is what gives off the foul odor. Fortunately, this odor usually goes away after a few minutes of running the air conditioner.

There are several ways to reduce this odor. First of all, try turning off the A/C compressor about 5 to 10 minutes before you turn the vehicle off, but keep the fan blowing on high on the outside air selection. This will dry most of the moisture in the case.

Second, you can spray some anti-fungal solution (like Lysol) into the intake area. On most vehicles it’s easiest to spray into the recirculation inlet inside the vehicle, usually under the right side of the dash.

This needs to be done while the ignition is on and the HVAC is set to recirculation, with the fan on.

If the recirculation inlet isn’t easy to access, spray into the inlet cowl (usually located on right side of firewall outside) with the fan on vent setting. Spray for about 30-45 seconds, then turn the system off and let it sit for 30 minutes.

About the Author

Dan Kincaid

Dan Kincaid spent nearly 27 years as a dealership technician. He is an ASE Master Technician in automotive, school bus, medium/heavy truck and truck equipment, and A/C certified by both ASE and ESCO Institute. He joined Mitchell 1 in 2001 and is currently a Sr. Technical Editor with the Commercial Vehicle Group.