I have a frtliner fld 120 and today when I had the heater switch on I hear air from the dash. This happens in the vent , heat, position but not in the defrost position. The heat still work in both position but you hear air. Put it in the defrost position and the air stop. Any suggesstion what might be the problem.

Thx in Advance

Vontrial

 

Does it sound like a mule braying??? We use to have one of those Freightliners, and the same exact thing happened in it... It drove me nutz!
If I remember hearing right, the air ducts were stopped up. (with what, I don't know.) The shop told me not to worry about it. (In other words...they weren't going to fix the problem. ) In our truck, there was no air coming from the heater. Just defroster. They finally got rid of that sorry piece of junk.

 

A fellow driver had that exact same problem. I forgot what it was. I know he had it fixed. seems like it was a air line, or a coupling in the line, but it needed to have a peice replaced to stop the leak. exact same symptoms though.

 

The peoblem was found behind the vent. in the dash. where the air was heard. sorry I cannot be more helpful.

 

Perhaps one of the vent lines is loose or not properly connected.

 

Had the same problem and I opened the dash and the switch had a loose connection, I just tightened the connection. Over the years I have heard several air leaks behind the dash and corrected them all by opening the dash and checking it out. If you can hear it you should be able to find it.

 

Would like to say thanks to each and everyone, will check behind dash this weekend. The temp suppose to be around 50 .

Vontrial