Dash off isn't a completely terrible job in my opinion- the more you do it, the better you'll get. But you're 100% right. It's not fun and something stupid will likely break. 124 is better than the 126 at least 😂 The vents are the PITA part with those stupid clips. Almost all of those tabs broke so I had to replace all 3 vents. For the pods themselves, I was able to 3 of part number 1248003075 and got them new. You can throw the rod out, re-use your existing rod, and then take off the top pink part and re-clock it to match the old one. Good luck!
Another helpful video, thanks! I'm all functional at the moment & finally tuned in (after 5 yrs) to the very distinct sucking, squeezing, slapping sounds coming from behind the dash. :) Just before winter I pulled the blower motor & wiper arm for essential lubrication & thankfully both have been given a completely new lease on life. I noticed at the time the awful deterioration of the foam on the fresh air flap so cleaned it up quickly & now it makes a clear "slap" when it shuts. I will strip everything down again & replace all the foam insulation & foam stripping etc during the summer. One question I hope you can answer - the AC module, I have the EC version. I believe my recent "stuck on" despite the settings AC issue is the module (given the clutch is fine, plenty of refrigerant etc). Are these supposed to remember their previous "power on" setting - I believe my AC unit used to always come back on with EC engaged if that's how it had been set now it only does it 50% of the time. Prior to removing & cleaning/some re-soldering, the EC button stopped engaging at all, I got it working again but it seems to only be 1 part of the issue. Fortunately plenty of used & NOS AC modules for sale here.
The dash is not as easy as a W201 or W123, but it's not awful. I would consider replacing the evaporator while the dash is apart, a common failure on these W124s, as well as the o-rings for the heater core. I did the job a few years ago and even then, the vacuum pods were difficult to source. A hint is there are only a few versions of the pods and the mounting of the pod itself and the arm is the same, so some of the pods can be sourced from other Mercedes or other German cars using the Behr vacuum pods. I also think some of the pods from later Mercedes (w202, R129, etc) could be modified to work, I've considered that for the long NLA defrost flap vacuum pod for the automatic climate control systems the W201s had. Another potential would be to figure out how to use motors like more modern cars, I suspect it could be done with some clever engineering but probably not a huge hassle.
note that this isn’t my first rodeo. I have done this job before when restored the red w124 i have also. On that car i bought the remaining NOS double diaphragm pods for the 126 you could still buy. One only required the rod changed, the other side required the bottom cap rotated as well as the rod. 1990 tempmatic cars without the heated central nozzle literally only have these 2 pods fortunately on the recirc flap. All other controls are manually operated via the right side knob.
With regards to your coolant temp differences between the two cars. There are different colour thermostat switches that open thermostat at different temperatures. I’m sure you know this but it’s something I discovered trying to find a cooling solution problem on my 2.5-16
If you do end up taking the dash off, please make a video about it. I am afraid this dreadful job is going to have to be done on my 300D at some point, as I think my heater core is on its last breath... When I turn the heat on, it works fine, and there are no leaks that I can notice, but after working for a while the cabin fills with a fog which I suspect is probably burning coolant... At least these cars were made so that they can be taken apart and put back together without any major hassle (relatively speaking).
My w124’s previous owner just duct taped the outside blower flap shut so its forced to recirculate permanently, and i believe he also blocked the vacuum to the pods, but hey it works so i’m not complaining, this is the blower box without the cabin filter , might be worth a try for your car?
I’ll think about it 😅 Though I have been informed someone is still making the diaphragms so might try a rebuild prior to unsealing the new old stock pods i have
