i have a w124 with the old r12 system. it's been putting out hot air for a while, and I think its time to fix it. everytime i hurt it on, i hear liquid running behind the center vents. not sure what the problem is. any ideas? thanks

 

I think it's usually the evaporator that fails (unfortunately, it's expensive, especially the install bill, because it's buried in the middle of the car (behind the center vents). I'm not sure about the sound you hear-that doesn't sound like an a/c problem.
Good Luck!

 

if its putting out hot air, it usually means its out of gas.

the water trickling sound is a common thing. it doesnt signify anything in and of itself. if it really bothers you you can go to the dealer and get an anti gurgle kit. but is hideously expensive once you factor in labour. all to make the occasional sound of water trickling go away.
not worth it.

 

I'm guessing that sound is from the coolant flowing through the heater core?