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1986 420 SEL
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62 Posts
Just to clarify, you must pull the dash to replace the evaporator, not the expansion valve.
Yeah you can replace the valve without pulling the dash if you hate yourself, your car, and life in general. You sure do get better access to everything once the dash is off though. Anytime I see a procedure that requires several crows foot wrenches and an amateur contortionist to complete, I try to look for a way to make it less painful. Also he's going on there to check the evap anyway. Removing the cruise amplifier to get to the brake switch was one of the worst experiences I have ever been through and that was with the seat unbolted. I am really not looking forward to pulling the column because the power adjustment is not working.
 

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1989 300SE 232k miles
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1,448 Posts
Discussion Starter #22
evaporator, expander, condenser, compressor. Gonna have to learn them.

Ok. I’m coming to terms with this being a replacement.

How can I tell what I can keep and what I need to replace in the system? All my repairs are on a super-thin budget. So cost is more important to me than time or work.

Obviously my Hi and Low connectors are r134a. And I assume my compressor. What else do I look at? How do I know if they’re converted to r134a? If they’re converted, how do I know if they’re working right or need to be replaced? Now that I’m aftermarket, how do I know which part to buy to replace things? ...OEM spec is so much easier.

I’m going to pull the evaporator, which means I’m going to replace it. I’m not getting in there and leaving it. ..unless there’s a way to flush it? So how do I track down the right r134a evaporator?

I’ll want to replace the o-rings. I know those are different between r12 and r134a. Will I need to replace hoses if the ones going to the evaporator are original and for r12? And if not, will the hose connections work?

...There’s an ‘87 s-class 300 diesel that just arrived at our salvage yard here. I can pull from that. But I have no idea what’s compatible with what.

Unless someone has an r12 system they’d like to see put to use. Cuz I’d be totally down to put that in.
 

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1989 300SE 232k miles
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Discussion Starter #23
Yeah you can replace the valve without pulling the dash if you hate yourself, your car, and life in general. You sure do get better access to everything once the dash is off though. Anytime I see a procedure that requires several crows foot wrenches and an amateur contortionist to complete, I try to look for a way to make it less painful. Also he's going on there to check the evap anyway. Removing the cruise amplifier to get to the brake switch was one of the worst experiences I have ever been through and that was with the seat unbolted. I am really not looking forward to pulling the column because the power adjustment is not working.
I’ve been meaning to pull the cruise amplifier. I’m getting constant, quick, pulsation at speeds over 45 mph. That’s one of the things I need to look at.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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Yeah you can replace the valve without pulling the dash if you hate yourself, your car, and life in general. You sure do get better access to everything once the dash is off though. Anytime I see a procedure that requires several crows foot wrenches and an amateur contortionist to complete, I try to look for a way to make it less painful. Also he's going on there to check the evap anyway. Removing the cruise amplifier to get to the brake switch was one of the worst experiences I have ever been through and that was with the seat unbolted. I am really not looking forward to pulling the column because the power adjustment is not working.
Hahaha! Your post cracked me up.

It's true that expansion valve replacement is challenging but I've read all the horror stories and went for it anyway. I found it wasn't that hard, really. I just had to use the tricks people mentioned, like removing that brace bar in front of it and loosening the mounting brackets for the hose in the engine bay.

Actually, I wouldn't hesitate to do it again, if needed. Naturally, if the dash is out that's the time to do it, though.
 

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1986/1990 W126
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14,322 Posts
I can say that the dash is actually kind of easy. I swapped my dash with a better one and it took pretty much spot on 5 hours start to finish. It comes out dead quick.

If you were to remove it, probably quite a lot else you could do under there if you wanted.
 

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1986 420 SEL
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62 Posts
You can just flush the evaporator. Brake parts cleaner would be my weapon of choice on that, as it should remove most anything in the system. Some expansion valves mention what refrigerant they are for with a sticker. If not there should be a part number you can reference on it so that you can see if it is for r134-a o-rings are both cheap and cheap insurance since your in there anyway. That link you posted is the one that tells how to change the valve without taking out the dash. It does have some good instructions for removing stuff though, so would be helpful for that purpose for sure. When you have the evaporator out of the car if you have a way to soap bubble test it for leaks with air I would recommend that as well as long is it cleans up inside and out ok. Good luck!
 

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1989 300SE 232k miles
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Discussion Starter #28
Awesome! I like repairs for the cost of O-rings and some cleaner!

And I expect I’ll need to buy a set of those crows-feet wrenches. I’ve made it this far in life without them, but that looks tight in there.
 

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1986 420 SEL
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Awesome! I like repairs for the cost of O-rings and some cleaner!

And I expect I’ll need to buy a set of those crows-feet wrenches. I’ve made it this far in life without them, but that looks tight in there.
Once you pop the top off the dash, you might find it easier to get to and be able to use a conventional wrench. I'm hoping you won't as it means I will need them too at some point.
 

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1986 420 SEL
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Once you pop the top off the dash, you might find it easier to get to and be able to use a conventional wrench. I'm hoping you won't as it means I will need them too at some point.
Wow, I'm glad you got the gist of what I said, because reading it back does not make as much sense as I thought it did when I wrote it. :oops:
 

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1989 300SE 232k miles
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Discussion Starter #31
I took it as if I remove the dash, I should be able to use regular wrenches. And that if I don’t need crows feet, that’s good. Because you’ll have to do this at some point. And you’d rather not need the crows feet.
 

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1989 300SE 232k miles
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Discussion Starter #32
Quick q: If I’m flushing the evaporator core, can I remove the expansion valve and flush it from there? Without removing the evaporator from the car?
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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Sadly, I think you do have to pull the dash to get to the evaporator. That's usually why when the systems are converted, it's not done correctly (expansion valve change requires dashboard removal) :)
In 2016, I was able to change both the expansion valve plus access & clean the upstream face of the evaporator without dash removal. It was not an easy job but can be done from under the left under-dash bolster/duct and after removing the blower fan on the passenger side.
 

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1986 420 SEL
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Quick q: If I’m flushing the evaporator core, can I remove the expansion valve and flush it from there? Without removing the evaporator from the car?
I would think you could, It would be impossible to tell if it "feels" clean inside thought. Also it might be a good time if you already have everything to that stage to "refoam" all the flaps and joints and such. make sure the pods hold vacuum, etc. The foam should be pretty cheap. Mainly labor doing the task.
 

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1989 300SE 232k miles
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Discussion Starter #36
I would think you could, It would be impossible to tell if it "feels" clean inside thought. Also it might be a good time if you already have everything to that stage to "refoam" all the flaps and joints and such. make sure the pods hold vacuum, etc. The foam should be pretty cheap. Mainly labor doing the task.
Gotcha. I do have the vacuum pod rebuilds and replacements. So doing the foam and such makes a lot of sense. Thanks
 

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Just to clarify, you must pull the dash to replace the evaporator, not the expansion valve.
I owned a 93 300SE with this issue, Had the AC go out at eight years old, I couldn't believe the cost when the dealer told me so I went out there, the hood was on the roof and the whole dash was on top of that, I believe some of the center console as well. The evaporator was leaking so they put in a new one and expansion valve, they charged 8k for the repair but it worked great for the next 6 years I had the car. It also stayed R12, it was done in 2001.
 

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1986/1990 W126
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W140? I've heard about the W140 air conditioning problems and expense. Luckily the old W126 is a lot quicker to deal with.
 

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1989 300SE 232k miles
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1,448 Posts
Discussion Starter #39 (Edited)
That’s great feedback on the ‘93. Im jealous of the r12.

My car was blowing at 48 F the other morning. It was 74 F outside, and cloudy. I realized (again) that when I put the fan on low, the blowing temp drops from 60 F to 48 F. To me, this is consistent with the evaporator not cooling properly. That it can’t chill all the air on high fan speed.

Also, at idle, it still creeps up to 70 F. Turning on the aux does not affect the blowing temp. However, raising he rpm to 2500 lowers the blowing temp back to 60 F (on low fan). I suspect my expansion valve is locked. And the compressor needs to increase pressure to push the Freon thru.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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Back in the days before W126 (!!) we were taught to test the A/C pressures at engine RPMS approaching or equalling that of 'Road Speed', roughly 18-2400RPM. At idle the values would drop so low that cooling was nearly not there..
This was on new or nearly new cars at the time and there was no ACC at the time.

Your experience of climate control output temperatures at idle ring a familiar tone.

On hot days up here in New England, I will often drop the transmission down a gear or two when faced with a low speed slog on a toasty day.. Ups the revs & drops the AC temp a bit.

Stay safe & cool man.

Good luck.

M
 
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