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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #1
A/C has been underperforming recently.
Bubbles in sight glass.

System has been working perfectly the 4 years previous to this since a major overhaul.

Driven relatively infrequently (except lately).

They just leak a bit over time in the real world?
Just a top off? or evacuate and start over (Scares me)>

Tj
 

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several
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23 Posts
Bubbles in the sight glass means that have an under charged condition. When you top off the system with a sight glass, you add right up to where the bubbles go away.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #3
Super.
I am meeting my Indy in an hour for a top-off.

Tj
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #4
Sucked down a 14oz can pretty quick.
Probably wants part of another but will try this for now.

Seems better.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #6
Its marginally better.

Here are the pre-charge readings at idle.
Outside temp was right at 100f.

IMAG1326.jpg

After charging the Low was around 43 and high 260ish with far less bubbles.

its all a bit of a mystery to me.
 

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1985 500sel and 500sec 2012 E63 1989 Porsche 911
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5,340 Posts
whats the max these cars can take


i recently put in 18 oz car gets cold if its in cool environment, but if sitting outside it still wont get cold

do i need more freon
 

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1990 560SEL
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61 Posts
Hot and Cold

My AC seems to want to switch off and on randomly. When it's working, it blows cold, but then it will switch off and blow hot for a while, then all of a sudden start blowing cold again. Does not seem to depend on the engine temp and it's not something I've been able to reliably reproduce, but it seems to work better when I'm cruising on the highway. Strange.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #9
Another pound of R12 added today and now the sight glass is clear and pressures a little better. System now seems to be performing like I remember it to.

The car has been on DD duty this summer by my partner, so I hadn't noticed the decline over the last few months.

Today we noticed the Fan clutch weak too.

Thanks for the moral support.
Tj
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #10
A/C is still weaker than it used to be.
Relatively cool this morning and on the freeway it blows 54f.

R12 recharged, pressures looked good to 2 different techs.
Fan clutch new, electric fan working normally.
Auto-system operating correctly. Fresh air vent working normally.

Whats next?
Verify evap drain?
Check temp sensors?
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,992 Posts
whats the max these cars can take


i recently put in 18 oz car gets cold if its in cool environment, but if sitting outside it still wont get cold

do i need more freon
1.3Kg or 2.9 lbs of R-12 or R-134a is nominal charge.

If you have access to one of those big Snap-On recharge machines, then the best route is to evac and re-charge from zero. Those machines have a leak down where if you have a leak, it will detect it and not let you re-charge. If all okay, then you can inject the exact amount into the system and know it's 'Full'.
 

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'84 500 SEC Euro 040 black Lorinser 2005 sl500
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2,516 Posts
Capacity of freon for 380/500/420/560 is 46 oz. of r-12 and 80% of that for r-134 which is 36.8 oz.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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Discussion Starter #13
Question was:
System filled to proper freon level, all obvoius parts working appropriately..
What next to check?

Drain lines?
Heat Exchanger or R/D sensor?
 

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'84 500 SEC Euro 040 black Lorinser 2005 sl500
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2,516 Posts
Question was:
System filled to proper freon level, all obvoius parts working appropriately..
What next to check?

Drain lines?
Heat Exchanger or R/D sensor?
Expansion valve would be next to check.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #15
I had two different A/C guys both check the pressures and both said pressures looked good. Would they have noticed an expansion valve problem? I hear that job sucks.
 

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'84 500 SEC Euro 040 black Lorinser 2005 sl500
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I had two different A/C guys both check the pressures and both said pressures looked good. Would they have noticed an expansion valve problem? I hear that job sucks.
I believe if the pressure is within spec on both the high and low side then you do not have an expansion valve issue. I have read that if one side is very high and the other very low then you may have an expansion valve issue which does not allow the correct flow of the freon.

I will browse through all my saved ac threads from the auto ac professional forums to make sure that info is correct. There is some really good general info on some of the ac forums that just don't show up on the Mercedes forums. Those forums gave me a really good general knowledge on the ac system.

If you get the correct crows foot type wrenches (about $8.00 for all three) and grind them down for clearance, the expansion valve job is a bit tedious but not horrible to do.
 

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1989 560SEL, 1979 Cressida MX32, 2006 F150 Lariat
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1,510 Posts
I had two different A/C guys both check the pressures and both said pressures looked good. Would they have noticed an expansion valve problem? I hear that job sucks.
I've heard that job was a royal pain and I am about to tackle the expansion valve job myself very soon.
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,992 Posts
Capacity of freon for 380/500/420/560 is 46 oz. of r-12 and 80% of that for r-134 which is 36.8 oz.
Sorry, I don't buy the 80% number. I just did this job on Saturday for the third time this summer, and at 80%, there are still bubbles in the sight glass, and it was operating inefficiently, and still needed the full charge.

I did it the first time in June when summer really hit. I had a slow leak and it leaked all out. Then I fixed the leak, re-charged it at a professional A/C garage here in town. They asked about the capacity because the stickers are removed on the front, and they looked it up in their book which read 2.9 lbs, and matched what the sticker says on my SEL which I told them what it was. They asked if it had been converted to R-134a, I told them it had been. They filled it with 2.9 lbs, monitoring the sight glass the entire time, and the A/C blew cold after they were done.

Then, after I discovered that I needed a new condenser and radiator, I took it over to Mauricio's, who just bought one of those new Snap-On A/C machines. I followed the procedure as indicated on the panel. At 80%, there are still bubbles in the system, meaning it is not filled to capacity. At about 90%, the bubbles went away, and I let it fill the rest of the way (to 100% or 2.9 lbs) and the air blows really cold now.

The temps that day were 105F outside air temp. 105F starting inside temp, and the air temp coming out the center vents was 57F degrees. Nearly 50 degrees cooler. After the car cooled down to mid 70's F, then the vent air temp went down to 47-46F.

My engine core temps have been very low now too since the new rad and cond went in. In city traffic, with 102 outside air temp, the car stays at about 85C, and only sometimes goes to 90C now.

All of my A/C and engine temp problems are solved now.

Maybe in a Gen I it's 80%.
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Discussion Starter #20
Maybe I am being too picky.
I did play with the Evap drains and I think the drive side one is not draining.

I guess its fine. Just seems like I remember numbing cold.
 
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