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1983 300SD
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781 Posts
Discussion Starter #1
My 83 300SD restoration is coming along more quickly than anticipated. I just bought a crack free dash and hopefully will be installing mid December.

While I have the dash out I want to replace everything back there that can go bad or become less effective over time. The vacuum actuators are obvious and IIRC the heater core is there as well. What other parts should I be purchasing?

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1991 560Sec
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68 Posts
I just pulled my dash few days ago and was going to make a post like this. Just commenting to get updates.

How do I know if I need to replace the actuators? I didn’t drive it too much before the full tear down.

Let me know if you have questions with removal I can try to help.
 

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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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1,731 Posts
Unfortunately, three of the 6 vacuum pods are now NLA. You will have to rebuild those 3 or transfer actuator parts to make this happen. Heater core for sure and A/C expansion valve for sure.
 

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1983 300SD
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781 Posts
Discussion Starter #4
Unfortunately, three of the 6 vacuum pods are now NLA. You will have to rebuild those 3 or transfer actuator parts to make this happen.
That's the impression I've been getting. But I'm only seeing two available. Is one of those used twice?

Regarding rebuilding the pods, is the consensus that this guy is the best source for the diaphragms? http://www.perfanalysis.com/climate-control/acc-version-ii/.

Ilyad, from what I've read you definitely replace or rebuild the vacuum actuators. It's a question of when they fail, not if. If it's cool I will 100% be pinging you about the removal. Some people have made it sound easy, others make it sound like major surgery.
 

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1983 300SD
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781 Posts
Discussion Starter #5
Went to the junkyard to practice removing a dash and do some shopping generally. Dash wasn't that bad. However, when we got to the HVAC / Heater box... that's big ol' nope right there. We couldn't even figure out how to get the damn thing out.

Couple of questions if anyone has answers.

How bad of an idea is it to not take this thing out, rebuild and replace the heater and evap core? I'm planning on keeping this car forever.

Is it really as bad as I'm thinking? The service manual makes it seem straightforward. That tangle of vacuum lines though...

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1989 SEL 560
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565 Posts
Went to the junkyard to practice removing a dash and do some shopping generally. Dash wasn't that bad. However, when we got to the HVAC / Heater box... that's big ol' nope right there. We couldn't even figure out how to get the damn thing out.

Couple of questions if anyone has answers.

How bad of an idea is it to not take this thing out, rebuild and replace the heater and evap core? I'm planning on keeping this car forever.

Is it really as bad as I'm thinking? The service manual makes it seem straightforward. That tangle of vacuum lines though...

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Removing the HVAC box is time consuming and intimidating but it can by done if you are well organized. Take lots of pictures from many angles, put screws and parts into marked baggies. Keep good notes during disassembly to help with reassembly.
I had a problem getting the box back into place with the flexible vent tube on the driver side. I didn't have it lined up correctly at first so it took extra time but it did work out. Having someone willing to help would be a bonus, especially to see obstacles and points of resistance.
The tangle of vacuum lines is not that bad. They are color coded. Take pictures and adhere notes to the various tubes.
I did partially screw up the flapper cable that works the passenger side vent. I have too much resistance to slide the lever more than half way. Fortunately I never use that vent control slider so it will sit in a half open or closed position. Make sure you know exactly where those cables are placed.
 

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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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1,731 Posts
R&R the dash and HVAC box is, IMO, an 8.5/10 on the difficulty scale. I would put rebuilding a W126 V8 engine higher. I have done this and it took two of us an entire weekend - about 20 hours for 2 people = 40 hours, and both of us know what we are doing with tools. And I had a complete HVAC box already rebuilt before we started (all new pods, heater core replaced, evaporator replaced, expansion valve replaced), so add another 20-30 hours for the HVAC box rebuild.
 

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1985 MB 500sel (Euro)
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153 Posts
My A/C has been stuck with only the defroster and the back seat outlet blowing air into the car. It works fine although takes a bit longer to cool the car. Luckily in Florida I rarely need the defroster and am tired of the outside windshield fogging up with the cold defroster air.

So, can I simply close some of the defroster vents and open the center and side vents? There is probably a good reason why not, since I can't find this "solution" in any of my searches.
 

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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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The pods, the A/C push button unit and the aux water pump are the 3 most likely issues you have, in order. If you have coolant leaking into your cabin, the heater core is bad. If you don't have A/C freon in your system and the compressor and expansion valve are good, your evap core is probably bad. Heater cores and evap cores don't fail that often. The pods will fail - especially if they are original. If you are taking the dash pad off to put a pad with no cracks, replace every pod you can and the expansion valve. If you really want to ruin a month of weekends and want piece of mind for many years, then take out the HVAC box and replace the cores. If it were me, I wouldn't take out the HVAC box unless I knew a core was bad - its a ton of work. Your pods need to be replaced. You should have Programa check your A/C push button unit or just send them your unit and get a rebuilt PBU - they fail regularly.

If you are taking the dash out, replace every pod with new and rebuilt pods. Don't jerry-rig the vents. Let the system work.
 

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1983 300SD
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781 Posts
Discussion Starter #10
Yeah, after playing with all of this on a car at the JY there's no way I'm pulling that HVAC box out. I'm just going to clean it up the best I can and replace whatever seals possible. It looks like some people are having decent results just pointing a garden hose at the evaporator. My main thing is getting all the mildew out.

I got an entire set of pods while I was in there and the new diaphragms are OTW. Expansion valve and PBU duly noted. Those didn't occur to me. Appreciate the input.

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1986/1990 W126
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13,419 Posts
There are good evaporator cleaning products out there, the type that foam up in there and then run out of the drain hoses. If yours has mildew it might take a few goes I guess.
 

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1983 300SD
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Discussion Starter #12
Do you have any thoughts on what would be too much on cleaning the evaporator? Basically, I'm planning on hitting it with the kitchen sink. I want to be 100% sure I've killed the mold, then clear all the gunk, then de-smell. At the same time, I reaaaally don't want to harm the evap coil or heater core.

Tentative plan is CLR mold/mildew, a biocide mildew bomb paired with biocide 100. To clear it out alternate between hose with soapy water and evap coil foam. Finally, chlorine bomb concentrated in that area of the HVAC system. Possibly pump full of ozone for 24 hours if I get access to a power outlet.

I'm tempted to hit it with a power sprayer at a car wash. That seems like it's asking for trouble though.

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1986/1990 W126
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13,419 Posts
Definitely not a power spray. I've heard people use a hose from a tap, but I was too scared so just went with a one shot product that foams out.
I didn't have any smell issues, was just trying to keep the performance good.
 

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1983 300SD
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781 Posts
Discussion Starter #14
Hmm. Based on the rest of the interior, mine is probably pretty rough. I'll get a diagnostic inspection camera, see what type of biohazard I'm up against. If it's as bad as I suspect (if I can even see it from the accessible side) I'll go really light with the hose, take some good pictures, try to provide a decent write up. I haven't seen many threads on battling a lot of mildew on a 126 evap.

That's going to be a few weeks though. Car is going in for paint in two days! Pretty excited.

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