Hello. First you want to make sure you don't have any codes in the climate system. Scan it with an appropriate obdII reader and once you eliminate that part of it, you can troubleshoot your vents, fan, module, etc. Fastest way for you to get a layout of what you're looking at is to get a printout from your dealer, for you vin vehicle, the layout of your system. Call the parts department or better yet stop by your parts dept at the mb dealer and tell them that your lower tube broke and you need to replace it. Depending who you run into, it might turn into a quick trip or a long one with the person asking a million questions. Reply accordingly.
Here comes the bad news... Those units in the GLs are 'one-part' units. If anything internally is bad, for ex., your heater core, blockage, etc., then you will need to replace the whole thing, not just the one part. More bad news, your whole dashboard will need to be removed in order to facilitate the removal/swap of the part/unit(s).
The good news is that I saved a bunch with Geico Car Insurance...
JK, I think you need a laugh at this point...More good news, your local indy or any MB specialty shop will do it for half the price then your local MB dealer.
Once you figure out the codes, post here and we'll go forward, until then it's just guess work. Hope this helps. GL. Happy Holidays.
