I have a 2004 VW Passat that has 75,000 miles. I have 5,000 miles before my next tune-up. Over the past couple of months, when I turn on my A/C, it smells foul for the first minute and then blows fine. I’m wondering what that may be…
The usual cause is a blocked drain. There are two to consider. The first is the one that drains water from the vents in front of the windscreen. Clean out any old leaves etc. Then turn the vent fan on high and spray the area with a Lysol type product. Use a full can. It may also be a condensation drain issue. I believe on the Passat the drain is in the engine compartment on the passenger side. Look for a “U” shaped cut in the aluminum foil insulation. It can be cleared by using compressed air or some string trimmer line. Take it easy with either as you don’t want to pop that hose off or damage it.
Which in turn allows moisture to sit too long causing the mildew which is what you’re smelling.
What position are you leaving the AC controls in when you park? You are not supposed to have it in recirculate (max) or off.