The other day I was driving my car, which has nearly 128,000 miles on it, with the a/c running. No problems were detected. I stopped to run some errands and when I got back into the car and turned on the a/c, it started making a very loud, obnoxious rattling noise, as if something was loose. Along with the noise was the smell ... awful, like a bad beach smell. I shut off the a/c. I turned on the a/c again when I got home, and the same thing happened. The smell now ranged from bad beach to rotting sauerkraut. Even with the a/c turned off, the smell is still there, but very mild. I also closed all the vents and opened the windows, but I can still faintly smell it. The a/c still emits cool air. Also, for the last couple of weeks, I have been hearing a very slight humming type sound coming from the vents, which I don't know if this was the start of the problem. I'm also going to open the hood and see if maybe an animal didn't get inside. Thank you!
What you may be hearing, is a dead mouse in your blower motor. As silly as this sounds it really is more common than people would think. Especially when it starts to get cooler in the evening, field mice find thier way inside HVAC systems of vehicles. These mice have a way to get in, but with the design of dash HVAC blend doors, they cant get back out and die. If you turn your recirculatory control on, spray OUST or Lysol odor control in the outside vents where your wipers rest. This is something (the smell) that you may have to deal with for a few weeks.
〉 Answered on Oct 15th, 2012 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions