Moisture in HVAC ducts

Y

Yoyogi71

Newbie
1971 Skylark Custom w/AC - I get an odorless mist/vapor when first turning on the heater or vent. Happens in warm and colder weather. It comes out of the dash vents and collects on the windshield. It clears off the windshield once heating up and using the deicer function. I tried running the vents with cold air for a few minutes before shutting down, but it doesn't help. The heater and AC work well. It's not a big issue but would like to resolve it, if possible. The car mostly sat in a barn before I got it 6 months ago. Could the drain hose from the (AC) system be clogged, and holding moisture? I would try blowing it out with an air compressor if I could find where it is located. Under passenger side?
 
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you don't have a water leak under the dash, do you? that might soak carpets and then the moisture would get blown around when the fan gets turned on.

are you running straight water or antifreeze for coolant? if you've got straight water in the engine, then a heater core leak would be odorless.


here's the 71 Chassis Manual, that will probably tell you where the drain line is:
http://www.teambuick.com/reference/library/71_chassis/index.php
 
Bob - I'm running antifreeze, and no water leak under dash. The mist comes out for about 1 minute then stops. Thanks for the chassis manual. I'm sure it will be helpful.
 
I run coolant in the car but there is no odor to the mist, no leakage under the dash, and the heater and AC both function properly. I also am not losing any coolant. I thought heater core at first too but decided not given these factors. Could it still be the core? Could it just need cleaned off?
 
Hey guys - I just got my head under the dash/glove box, and with a flashlight noticed one tiny drop of coolant, that hadn't made it onto the carpet. It looks like it is indeed a bad heater core after all. Dang.
 
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