Humidity while running the heater

[vanhaaren]

2002 Montana. Regardless of the temperature or season, when I run the heat, the cabin is instantly humid and the windows are fogged up within a minute. The floors are dry. The heater core is DRY.
Here's the strange part; with the temperature set high I can stop the humidity by hitting the AC switch on. It will then blow warm DRY air.

[mastertech1964]

there has to be water getting into the car somewhere somehow, turning on the a/c does dry out the air in the interior thats why most cars automatically switch on the a/c compressor in defrost mode to help with defogging the windows

[vanhaaren]

o.k., let's say I have a very slow leak in the heater core (slow as in maybe it's just releasing some steam). Would it make sense then that the a/c control turned on would remove that 'steam'.
The thing I don't like about that theory is that when the heater is on and the air is humid, I don't smell antifreeze and there is no greasy film on the windows.

[3100]

Originally Posted by vanhaaren

o.k., let's say I have a very slow leak in the heater core (slow as in maybe it's just releasing some steam). Would it make sense then that the a/c control turned on would remove that 'steam'.
The thing I don't like about that theory is that when the heater is on and the air is humid, I don't smell antifreeze and there is no greasy film on the windows.

Is your antifreeze level decreasing slowly? This still sounds like a heater core.

[vanhaaren]

yeah, a slooooww leak is present. But I can't smell anti-freeze in the 'humid' air. My mechanic's been at the heater core twice and it's been DRY. That's why I'm thinking that maybe it's just a steaming leak once it's hot and under pressure.
The A/C switch still confuses me though. The A/C can't really be running when I have the temp set to HOT and it's cold out....can it?