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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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Discussion Starter #1
I’m working on the AC of a 2008 SL 550 I have flushed the evaporator, replaced the expansion valve, receiver dryer, compressor [Denso 471-4117], and condenser.

The system was recovered before the parts exchange, pulled a vacuum for 45 min followed by a leak test and then charge with 2.03 lbs of 134A through the low side port using a Robin Air 34778 AC machine.

The static pressure [ambient 82 degrees] is 90 PSI low and 92 PSI high.
When I first start the car the center vent outlet temperature quickly drops from 82 > about 68 degrees after which it starts climbing back up to 82 degrees.

At that time the low reads 70-85 PSI and the high 350+ PSI

So it appears the compressor swash plate keeps pumping at high volume and not getting the right signals from any relevant sensors.

I have swapped the evaporator sensor from another car that has no ac issues but that did not resolve anything.
At this point I’m kind of at a loss of what to try next any ideas or tips based on past experiences with similar symptoms would be welcome.

Q; how many other sensors are here to check on beside the ones in the AC control unit.

SDS reports no faults.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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low reads 70-85 PSI and the high 350+ PSI
Too high, that's the cut off for the compressor.

Cooling fan runs when you turn on ac?

Check refrigerant pressure via SDS, what is it reporting and compare to gauge reading.
 

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Outstanding Contributor
2003 SL500, 2003 SL55, and four R129s
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My static pressures are typically around 70 PSI.
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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At 82F ambient, R134 should be just under 50psi on the low side, and around 230psi on the high side. Yours seems too high, so I'm thinking the condenser is not getting cooled enough.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #5
Thanks to all of you for your taking the time to reply.

What I had not stated in my original post was that I had left out the SL 550 Rad cooling fan (as I never had heard it run before) and was using a large electrical shop fan (old school method) when I was running my pressure test after charging the AC system with my Robin Air 34788 (2.03 lbs) well Deplore question if my cooling fan was running got me to realize that perhaps there is a feed back from the Rad fan when it's installed to the AC controller.

So I got a fan from another SL550 that is currently in my garage installed it and and indeed the running fan changed the conditions to about 70 PSI on the low side and 135 PSI on the high side. (Which indicates a damaged compressor)

At this time I believe that the high pressure conditions during the time that I was running without a working rad fan has damaged the compressor and it needs to be replaced to get the pressures in the 30-225 PSI range.

I'm attaching the pictures of my SL55 P30 AC pressures that is running just fine and producing 27 degrees from the ctr vents also a picture of the SL550 with the wrong pressures and screenshot of the SDS test that also point to a damaged compressor.

After I get a replacement compressor installed I will report back here and perhaps on the lessons learned here the newer swash plate AC compressor controller require feed back from the rad fan regulator, the old external clutch type compressors don't.

BTW; I did look through my hard copy SL ETM' for a wiring diagram of the rad cooling fan if any of you can point me to where I can find it I would appreciate it.
Also as you may now to get the lower bolts out of the AC compressor is a b**ch so I drill an access hole in the crossbar which makes it real easy (see attached picture)

Again thank for taking the time to assist.

Happy motoring SL55 P30 AC static pressure.jpg SL55 P30 Run pressure.jpg SL55 P30 Vent outlet temp 27.jpg SL 550 Run After FC.jpg
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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M4/7 is the cooling fan.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #7
Well I installed the replacement compressor together with a new dryer (this is the 3rd one) and I'm still having the same problem 80 PSI on the Low side and 155 on the high side I have replaced every darn thing apart from pulling the dash and taking a look at the evaporator.

The system holds vacuum and passes the leak test from the 34778 Robin Air

I have swapped the control unit for a known good one any more ideas what to try next?

This one really got me puzzled.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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How is the ac performing? Not cold anymore?

What is refrigerant pressure sensor showing?
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #9
I have reduced the amount of oil in system (by opening the condenser in and out line and blowing it out with nitrogen) and so far the AC dash vent go from 82 degrees down to 68-70 the refrigerant pressure is at 60 and 200 when I ref the engine to 1800 RPM.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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68-70....too high still. Properly functioning should go down to 45-50f when set to LO LO.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #11
I realize that as on my own SL55 it gets down to 38 f at the ctr vent.

On this SL550 the vent outlet temperature starts to come down when I reduce the amount of oil in the system however so far to get the low side pressure down in the 30-45 PSI range appears to be the remaining issue.

So in my mind I'm thinking that either I still have excess oil lingering in the evaporator or the evaporator fins are packed with dirt (the old carbon filters where really dirty) causing poor heat exchange with the passing airflow (reason that the pressure does not drop to the 30-45 PSI range) however the amount of air coming from the vents is abundant.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Again, lets go back. What does the refrigerant pressure sensor says on SDS? The AC compressor has a cut off point, and it uses the pressure sensor and evaporator sensor as data point to manage the compression ratio.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #13
Ok thanks for keep on pointing me in the right direction.

In the first attached SDS screen shot you'll see that
B10/6 Evap temp is 19C
B11/4 Coolant is 42C
Compr = 7 Bar

The second SDS screen shot
B10/6 Evap temp is 22C
B11/4 Coolant is 81C
Compr = 12 Bar

The third SDS screen shot indicates;
The Refrig Pres is ok at 12 Bar
The Refrig level is OK I used my Robin Air to charge 2.03 lbs
Coolant is well below > 119C
Evap is well above <2C
Which leaves open the emergency switchoff "ON"

The fourth SDS screen shot has a possible cause that I'll need to check out.

Let me know if you any other suggestions.

Thanks

2662354
2662355
2662356
2662357
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Problem is the evaporator temperature does not move at all. Possible culprit could be a few things.

As you compress freon, the higher the pressure, the colder it becomes (with respect to ambient temp). So at 12bar it should be approximately 5C or so at the evaporator. While driving, the pressure should drop to about 7bar, but provide the same evap temperature due to cooling.

So, from my perspective, it could be a clogged evaporator, dirty freon (especially if you use the off the shelf ones with "sealant" or "oil" or any other addictive -- most AC systems do not like that, not just MB.

How did you flush the evaporator? I'm thinking you might need a evaporator replacement, since any sort of flushing tends to clog either the evap or the condenser.

But all depends on what freon you used.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #15
I flushed the evap by using a quick flush canister from O'Reilly. From my observations I did have good air flow through the evap after the flush.

The Freon is from a newly sealed 30 Lbs container using my Robin Air 34778. (See attached) every other car I have serviced with this unit has excellent AC.
2662432


So now I'm at a toss up get a better flushing system or pull the dash and replace the evap. The system has no problem holding vacuum and the airflow from the vents is good.

I guess I have to search my WIS for the dash removal procedure for the R230 and check it out.







I
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #16
Well I decided today to remove the dash (see attached) and get a new evaporator.

I have spend more time recovering, pulling vacuum and recharging this system than I care to know so I trust that with the new evaporator installed i'll get the low and high pressures in the desired range.

I'll report again when I have more facts.

Thank you - Deplore for helping out much appreciated.

Best HK
2662515
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Jeez, that's pretty impressive. Big job.

I think the evap should do it. When you put in the new evap, pull a vacuum and leave it there as you assemble the dash back together. It should hold vacuum throughout the whole time.

What of the expansion valve? You said you used an aftermarket unit?
 

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Coupe/Convertible Forums Moderator
CURRENT: 2011 SL550 FORMER: C300, ML350, CLK550 Cabriolet, C240, ML320, 300TD
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Not only do Herman's DIY skills make many of use look like bumbling fools he'd probably embarrass more than half of the professional technicians out there.
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #19
Jeez, that's pretty impressive. Big job.

I think the evap should do it. When you put in the new evap, pull a vacuum and leave it there as you assemble the dash back together. It should hold vacuum throughout the whole time.

What of the expansion valve? You said you used an aftermarket unit?
When I have the old evap out I'll clean and run it through it's own vacuum/pressure test on the work bench before I'll pay coins for a new one. I looked yesterday and prices for this model (part # 230 830 06 58) run from $600-$1000 +

Than I found a complete used HVAC unit out of an SL65 (see attached pictures) that looks really good so I went and bought it in addition to buying just another stand alone evap replacement for the old one if it does not pass my bench testing.

2662585


2662586



The after market expansion valve story;
Before ending up replacing the condenser I had replaced the compressor together with an after market expansion valve and dryer as that's kind of the standard thing to do when you're replacing compressor.
As part of my ongoing pressure issues after the compressor install I re-examined this expansion valve and found that the valve operating stem (needle) could slide up and down (using a plastic needle nose pliers perhaps 2-3mm) before it would make contact with the spring loaded valve cap.

The original expansion valve (the one I had removed from the car) than got tested the same way and I found that when properly calibrated ( I put markings on it before unscrewing the spring loaded valve from it's seat) there was zero play between the needle and the valve cap. So I believe my original expansion valve never was an issue.

I'm adding some pictures of the expansion valve testing I did for further clarification.
2662587

After market EXP Valve has play between needle and valve cap

2662588
Original EXP V

2662589
Original marked before removing the valve cap

2662590
Original side view

2662591
Original there's no play between needle and valve cap

2662592
Original looking inside to the seat where the valve cap rests

2662593
Original spring loaded valve cap removed from the "H" block
 

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Premium Member
2007 SL55 AMG P030 -2007 S65 AMG
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281 Posts
Discussion Starter #20
Not only do Herman's DIY skills make many of use look like bumbling fools he'd probably embarrass more than half of the professional technicians out there.
Rodney,

Your to kind I want to be just like you! :D

Best H
 
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