I recharged my A/C recently, and now it's doing what it did back in the day. It's plenty cold when it's on, but it also puts out cold air when it's on defrost even if the A/C is turned off. It also has a slight hissing sound when the A/C is on, or when it's on defrost (with the A/C off).

Why would it feel like A/C is coming out of the defrost vents when the compressor is not running?

 

You might consider looking for a vacuum leak. Check the vacuum lines and controls inside the vehicle as well as under the hood. Depending on whether the vehicle has manual or automatic climate control, door positions and direction can be vacuum controlled.

 

I'm sure it's manually controlled. I do believe they're operated by vacuum. I've looked under the dash and moved the controls. Everything seems to work properly. I might have to do more investigating into a possible vacuum leak under the dash. How would that allow a/c air to come through when the a/c isn't running? Is it just not sealing something, and the residual cold air bleeds through for a while?

 

The system is designed to default to defrost position as a safety measure in the event control is lost during rainy or cold weather.
Control apparently has been lost very possibly due to loss of vacuum to place the doors in the position selected by the operator. If you can hear the vacuum leak inside the vehicle start looking inside. You might need to remove the glove box to get to where it might be leaking or a hose came off. A little detective work pays big dividends.

 

Thanks for the tip about the glove box. Easy enough to remove that 'cause the cabin air filter is behind it. I'll do some detective work soon and let you know what I find.

 

A bit more investigating makes me realize the a/c is turning on whenever I put the climate control in defrost. Is it supposed to come on automatically? I'd rather turn it on when I need it, not have it on a/c any time it's on defrost. Is that a feature, or something I should have checked out?

 

The A/C compressor does come on when defrost is selected. That is so it dries the air to the windshield. There usually is a temp sw in the syst that prevents the compressor from coming on when it is really cold out.

 

OK. I'll have to wait till cold weather to see if that switch is working. I'd still rather have it like my 1997 Accent where I could turn on the a/c to defrost the windshield if I wanted. Thanks for the feedback.