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1989 300SE 232k miles
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Discussion Starter #1
Hello All,

This regards my 1989 300SE with 234k miles. I’ve owned the car for about a year and put about 3k miles on it.

The AC system was converted to r134a by the PO. She stated it never ran cold afterwards. It was done by a local store of a national chain.

Last year, after much research, I added enviro-safe r134a replacement to it. It would consistently blow about 20 degrees colder than the outside temperature. I then found my recirculation flap wasn’t working (bad pods). I forced that open, and the car blew a little colder. I recently repaired the pods and my recirculation flap works properly.

Recently, the car started blowing warm again. The last two weeks it blew warmer when sitting, and I noted the aux fan wasn’t coming on. I jumped the fan, it works, so I expected the problem to be low pressure in the AC system. Also, my car’s engine has been running warmer, so I replaced the viscous fan clutch this morning.

Today I vacuum drained the AC system using a full gauge set. I then started the car, turned on the AC at its coldest setting, with recirculation on. I added some enviro-safe using a handheld hose and gauge. Then, once the compressor was kicking on, I added some PAG oil. Then I added more ES. At this point, I watched my handheld gauge and sight glass. My gauge read 25 psi, and the sight glass was frothy yellow-ish. I added more ES. The gauge started fluctuating between 35 and 45 PSI. The sight glass looked less frothy. I added more ES. The gauge moved between 45 - 55 psi. (55 psi starts the red zone) The sight glass started cycling between frothy and clear. The cycles of psi and frothy/clear are not in sync.

Inside the warehouse, the ambient temperature was 80 F degrees. The blowing temp was 80 F degrees. The engine temp was 80C degrees. And the aux fan was running.

I then drove the car on the interstate for 25 minutes. The outside temperature was 90 F degrees. The blowing temperature dropped to 60 degrees while on the interstate. Once off the interstate, when stopped, the blowing temp rose to 70 F degrees.

That’s where I am. On the highway, it blows 60 F degrees. On the back roads, it blows 62 F degrees. At a stop, it blows 70 F degrees. My aux fan is working as it should.

The sight glass cycles: 3 seconds clear, then 8 seconds to froth back to clear, 3 seconds clear, 8 seconds to froth back to clear. Yes I did time it. Yes it is that rhythmic.

But I’m unsure on how to proceed. I read that frothy in the sight glass means low on Freon. And to add more Freon. But not too much. Too which. my Low side pressure is reading 55 psi.

My instinct is to add more ES. I barely added a can. And that’s way low by weight, especially with an empty system. And it seems adding more Es brought clarity before. And clarity in the sight glass is what I want.

Suggestions? Input? Ideas?

Thanks,
Bill
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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What's the pressure on the high side? How long did you hold the vacuum on the system before you started adding refrigerant?
 

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Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,516 Posts
John has raised some good points above.

I am joining a little late here, that said.. I have read EnviroSense instructions.. If I am correct, it is recommended one use their proprietary 'stop leak' then charge the system?
Perhaps I am misinformed?

Anyways, here is a charge reference including R-12, R134a.. Ambient temperatures & humidity variants..

One of my cars is still R12

My later car came with R134a from new

Chilling in here New England.

M


Refrigerant Charts.png
 

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1989 300SE 232k miles
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Discussion Starter #4
What's the pressure on the high side? How long did you hold the vacuum on the system before you started adding refrigerant?
I never looked at the high side. I can do that tomorrow. I ran the vacuum for 30 minutes. I had it hold for 10 minutes.
 

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1989 300SE 232k miles
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Discussion Starter #5
John has raised some good points above.

I am joining a little late here, that said.. I have read EnviroSense instructions.. If I am correct, it is recommended one use their proprietary 'stop leak' then charge the system?
Perhaps I am misinformed?

Anyways, here is a charge reference including R-12, R134a.. Ambient temperatures & humidity variants..

One of my cars is still R12

My later car came wit R134a from new

Chilling in here New England.

M


View attachment 2634201
What I read was to only add the stop-leak if there was a leak. Add the first can, add stop leak if there is a leak, and then add from the second can. I do have a can of their stop leak.

This chart is interesting. Because I’m somewhere around 70% humidity, and 90 degrees. Which puts the psi and blowing temps at r12 specs.
 

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1986 420 SEL
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57 Posts
You know since you had they system apart you probably should have replaced all the o rings especially if their not green (Viton). I question the quality of the work done for the previous owner. Shops do not charge enough most of the time to cover what should be done to the system to retrofit it properly. (Hence since they don't want to spend too much time on it they half-ass it) People like to take shortcuts like not replacing the expansion valve and that would most definitely make the air temp wrong. Stop leak in my opinion is designed to get you through one summer before you can pull the system apart and find the actual leak. It ends up causing more issues than it fixes most of the time. I'm not sure I would have added oil not knowing what the amount in the system is already. The whole thing probably needs cleaning out completely and making sure it has the correct amount of oil in the system. Then you pull a vacuum for a good hour or so in the heat should get any water out of the system. I wonder how old the compressor is?
 

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1989 300SE 232k miles
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Discussion Starter #7
I have those same concerns, particularly of them not changing all the parts. I’ve had the car for 1 year. She had it for 3. The most we’re looking at is 4 years.

I just added a bit of oil because I have vacuumed the system twice.

We’re coming into hurricane season. And that’s kind of the point of this car. I’d really rather not get into ripping the AC system apart. And, because it’s an “upgrade,” I wouldn’t know what to replace. Or where to get matching parts.
 

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1989 300SE 232k miles
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Discussion Starter #8
I checked the psi this morning. It was 50 psi Low, 225 psi Hi. And I know that’s terrible. So I emptied by and vacuumed the system again. And made sure it held pressure, again.

I refilled it with ES until the aux fan kicked on, and checked the psi. It was at 30 psi Low, 150 psi High.

Because it’s over 80 F degrees here, I went to 40 psi Low, and it stayed at 150 psi High. The sight glass it frothy all the time. That’s where I left it.

It’s 90 F degrees outside, the car’s blowing 60 F while moving, creeps up to 70 F at a stop.

It may be that with this changed system, being in Florida, this is the best I’ll get.

Oh, an I just got all the diaphragms to rebuild the climate control vacuum pods. After I did the recirculation flap, the others blew. Maybe that’s a factor...
 

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1986/1990 W126
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Surely it should get colder than that. I dunno about the Florida bit, my air con guy said the AC in my SE was like 4 times bigger than a normal car.

It was awesome even with r134, until after needing a new compressor. Set up new Denso compressor as per guidelines, it was mediocre at best and the aux fan always ran. And it never used to beforehand unless the motor got hot. It took quite a bit of dialling in actually, it was the pressures not being what he thought they should. He did it by ear as we watched the compressor cycle on and off, adding more gas until it started to behave more normally. Also checking the vent temps. It's been great since.

However that's max ambient temps of about 30 celsius, I imagine way less humidity.
 

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1986/1990 W126
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14,136 Posts
I forget what we got the vent temps to, maybe 8 celsius or something. At idle but at that point not such hot weather.

It's frustrating having shite AC in a car like this isn't it. It should be awesome. Unconverted, they do a proper 'wall of cold' when you start the car.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,516 Posts
On my R12 system I generally see no to a very very few bubbles in the sight glass when the compressor is cycling..

The R134a system, filled by exact weight & blowing ‘ice cold’, presents a frothy view in the sight glass.. One time I added more 134a thinking it was not correct or under-charged due to this foam. Well all I accomplished was to reduce the cooling capacity considerably by for sure over-charging the system.

Once vacuumed out, and the exact amount [by weight] added.. the system preforms as new again.

As an FYI here, another thought comes to mind.. My 560, I had found the cooling output insufficient, using a boroscope I had found the evaporator face nearly 50/60% clogged with a grey fuzz & mouse nest evidence. It seems some time in the past, mice had worked their magic up in there. There was very poor airflow coming through.

That was Summer 2016 & I did a write up on it at the time....

Might it be possible there might be reduced airflow across the evap too? Our youngest W126 example is now close to 30 years old.. When the car is shut off / stored etc. the fresh air/ recirc flap hangs open.. allowing critter access if you will.

My car just can’t be tho only one so affected..

M.
 

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1989 300SE 232k miles
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Discussion Starter #12
Surely it should get colder than that. I dunno about the Florida bit, my air con guy said the AC in my SE was like 4 times bigger than a normal car.

It was awesome even with r134, until after needing a new compressor. Set up new Denso compressor as per guidelines, it was mediocre at best and the aux fan always ran. And it never used to beforehand unless the motor got hot. It took quite a bit of dialling in actually, it was the pressures not being what he thought they should. He did it by ear as we watched the compressor cycle on and off, adding more gas until it started to behave more normally. Also checking the vent temps. It's been great since.

However that's max ambient temps of about 30 celsius, I imagine way less humidity.
This is my kind of reply.👍
 

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1989 300SE 232k miles
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Discussion Starter #13
One thing I did observe this morning: Outside temp was 73 F degrees. The car blew 60 F degrees.

When the outside temp was cold like that, I’ve had it blow colder than that in the past.
 

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1989 300SE 232k miles
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Discussion Starter #14
On my R12 system I generally see no to a very very few bubbles in the sight glass when the compressor is cycling..

The R134a system, filled by exact weight & blowing ‘ice cold’, presents a frothy view in the sight glass.. One time I added more 134a thinking it was not correct or under-charged due to this foam. Well all I accomplished was to reduce the cooling capacity considerably by for sure over-charging the system.

Once vacuumed out, and the exact amount [by weight] added.. the system preforms as new again.

As an FYI here, another thought comes to mind.. My 560, I had found the cooling output insufficient, using a boroscope I had found the evaporator face nearly 50/60% clogged with a grey fuzz & mouse nest evidence. It seems some time in the past, mice had worked their magic up in there. There was very poor airflow coming through.

That was Summer 2016 & I did a write up on it at the time....

Might it be possible there might be reduced airflow across the evap too? Our youngest W126 example is now close to 30 years old.. When the car is shut off / stored etc. the fresh air/ recirc flap hangs open.. allowing critter access if you will.

My car just can’t be tho only one so affected..

M.
I was thinking this. I’m going to pull the dash as apart as I can without actually taking it apart when I redo the rest of my vacuum pods. I’ll look.

And that observation on the frothy Freon is interesting. Thanks!
 

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1986/1990 W126
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I've read on here the sight glass is kind of defunct with R134. Malcolm is the man to know, an AC expert really.

I remember that write up, I did buy an expensive foam cleaner after that with a slight improvement in cooling I thought. No rodent nests, just general dirt.

My dual wheel system doesn't see any use of the recirculation flap really, almost never close it. I think the fully automated system most US cars came with make more use of flaps and pods, and revert to defrost mode if challenged. For safety.
 

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1989 300SE 232k miles
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Discussion Starter #16
On my R12 system I generally see no to a very very few bubbles in the sight glass when the compressor is cycling..

The R134a system, filled by exact weight & blowing ‘ice cold’, presents a frothy view in the sight glass.. One time I added more 134a thinking it was not correct or under-charged due to this foam. Well all I accomplished was to reduce the cooling capacity considerably by for sure over-charging the system.

Once vacuumed out, and the exact amount [by weight] added.. the system preforms as new again.

As an FYI here, another thought comes to mind.. My 560, I had found the cooling output insufficient, using a boroscope I had found the evaporator face nearly 50/60% clogged with a grey fuzz & mouse nest evidence. It seems some time in the past, mice had worked their magic up in there. There was very poor airflow coming through.

That was Summer 2016 & I did a write up on it at the time....

Might it be possible there might be reduced airflow across the evap too? Our youngest W126 example is now close to 30 years old.. When the car is shut off / stored etc. the fresh air/ recirc flap hangs open.. allowing critter access if you will.

My car just can’t be tho only one so affected..

M.
I’m thinking this evaporator May be a very real source of my problem. Do I need to pull the entire dash to get at this? What am I looking for when I find it? And how do I clean it?

I mean, if I’m doing the hard to reach vacuum pod stuff, it may be easiest to take the whole dash apart. And I need to look at my odometer. That stopped working recently. So that’s just a step in removing the dash.
 

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1986 420 SEL
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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) You may find the evap weighs more than it should if someone has pumped a ton of stopleak in it before. Good luck and may your car blow cool air sooner rather than later. :)
 

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1989 300SE 232k miles
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Discussion Starter #18
Ugh... I’m leaning toward someone pumping a ton of stop-leak into this, and restricting flow. And I can’t imagine them pulling the dash out to replace that. Just because the car’s properly put together.

I drove it last night. 70 F outside. I turned the climate control to max and let the car idle past normal operating temp. It blew 80 F the whole time idling, even when the aux fan kicked on. I then drove it, and it dropped to 60 F. Stopped at traffic lights it crept back to 70 F.

So, it’s hitting that floor temperature-wise. And creeping up when stopped. But blowing warm at the start, that’s new. Sarcastic Yeah!!
 

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1986 420 SEL
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Yeah if they didn't pull the dash and replace the expansion valve it will never work right. In fact it's surprising that it cools at all considering the very different specs of the two refrigerants. I bet they charged the PO an ass-load (imperial not metric) of money to "convert" the system as well. I'm not sure what actual temperature differential you will get in the end, but it will be better than that awful excuse of an A/C. My Volvo's leaks down right now over a summer, but at least when it's charged it blows ice cold!
 

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1989 560SEC, 1989 560SEL, 1995 E420
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Just to clarify, you must pull the dash to replace the evaporator, not the expansion valve.
 
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