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There is a relatively unpleasant smell in my car's HVAC, AC or heating system.

Failed idea#1: I removed the cabin air filter and sprayed lots of Lysol in there. It did not help much.

Failed idea#2: I asked my mechanic and dealer if they can open the HVAC/AC and clean it. It seems that it is 2-3 days job and costs ~2000$. Not an efficient option.

Idea#3: There are sprays that guarantee to eliminate mold smell from the car AC system; however, I guess it just hides the odor, and I am not sure it removes the actual mold or bacteria.

Idea#4: I am thinking to spray 3% oxygen peroxide (or alcohol) there, but not sure if this idea causes any damage to the system. Should I do this?

Is there any car HVAC/AC cleaning solution or technique that helps with cleaning the HVAC system?

Update1 The car is Camry 2007. Everything other than AC odor is in a decent shape.

  • Describe the odor. I have cars that are over 20 years old and over 300,000 km, I've never had to clean the inside of the HVAC. – tlhIngan Oct 14 '16 at 18:37
  • Knowing what make and model would help. – CharlieRB Oct 14 '16 at 19:20
  • "alcohol" I'd say that's a big no-no seeing as it's flammable and you cannot know there won't be open spark or static. Could end up with a really nice explosion in a closed tube! – justinm410 Oct 14 '16 at 20:19
  • Do not spray random chemicals across radiators! Your heater core is very expensive to replace. Radiators are made out of various sensitive metals that are designed to transfer heat well, tolerate air on one side, and water/anti-freeze/R134a on the other side. That sensitive metal is susceptible to chemical reactions with unknown chemicals. At best, it'll just alter the surface so it transfers heat worse. At worst, your evaporator will get pinhole leaks. – Zach Mierzejewski Oct 14 '16 at 21:48
  • @tlhIngan: it is moisture and mold odor. It depends on living in a humid area as well as how efficiently the car AC system can bypass the moisture. – Allan Xu Oct 15 '16 at 1:58
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If you want to do it yourself i'd suggest the peroxide. First of course double check that it won't harm the interior or trim. The HVAC system is meant to deal with some amount of moisture and peroxide is just that, water (with more oxygen). Don't use alcohol because it's flammable.

To accomplish what you want, first remove the cabin air filter. Then place the HVAC system in recirculate mode. Find the recirculate intake under the dash. Running the fan on high set the knob to full cold and gently mist the peroxide into the vent. I said gently and mist. Don't squirt or spray it in there. Don't do a lot either. Then turn the knob to full hot and do the same thing.

That said there are two commercial services you could find. One uses a special machine to make a mist that is drawn through the HVAC system. The other uses and ozone generator to flood the inside of the car with ozone. Ozone is deadly to live things and will kill any bacterial or fungus or smell causing things in the car. I would recommend the ozone method.

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Taking the vent system apart is rather simple for most vehicles and usually only involves a screwdriver. It is a lot of work, but not difficult by any means and if you have a spot where you can work (garage), you could easily tackle this yourself and give your vent system a good cleaning.

Find a repair manual for your vehicle (Haynes or Chilton), they will have a section on how to take the dash and central console off, that will give you access to the actual vent network.

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    I take it you've never spent 18 hours replacing an evap core or blend door on a car or struck. – vini_i Oct 14 '16 at 19:45
  • @vini_i No I haven't. The original poster just wants access to the vents to give them a good cleaning. – tlhIngan Oct 14 '16 at 20:58
  • I assume it depends on the model. My car is Camry 2007. The way that my mechanic explained, I need to completely open and remove the dashboard. Then open the heater and AC unit. He explained that it is at least two days job and involves many complexities related dashboard disassembly. – Allan Xu Oct 15 '16 at 2:02
  • Removing a dash is not that complicated, I just removed mine this afternoon to diagnose a dead HVAC fan. Your mechanic just doesn't want to do it. If you have the proper schematic from a maintenance manual, it will tell you where the screws are. – tlhIngan Oct 15 '16 at 2:21
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Ozone treatment could help, but if there is excessive mold formation inside, you will need to get the dashboard removed, there is no way out of it. However, in most cars its about a 5-6 hour job. I got it done recently, and it took about 5 hours. Of course, cost was far far lesser as in India labor is very cheap.

If you want to try DIY, I would say remove the vents and keep silica gel there. Run recirculation mode with windows closed for some time, it will pull in the moisture, but may not help beyond a few more days.

  • What model is your car? – Allan Xu Oct 15 '16 at 3:13
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I would suggest you to heat up the entire system before using chemicals or disassembling it. There is no guarantee for success but you won't have costs nor risks and chances are that the heat eliminates the mold. It could be possible that the mentioned practice is not viable with an automatic regulated hvac system.

You just need a place where your car can idle undisturbed (and local laws do not prohibit such things).

Just drive your car until the engine is hot, park it and let the engine idle, turn on the heat and fan to maximum levels, switch on the air circulation, exit the car and close the door. Let it heat up for some time (20 minutes where enough for my car), then ventilate your car thoroughly and check if things got better. This works even better if you practice it in hot weather with full sun exposure.

To prevent further mold make it a habit to turn off the ac some minutes before turning off your car.

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