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2011 Mercedes E550 ac will not start up


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oldmots
Novice

Jul 21, 2022, 1:19 PM

Post #1 of 10 (241 views)
2011 Mercedes E550 ac will not start up Sign In

My Mercedes E550 AC compressor will not start up when the car interior is hot. If I gun the engine, most of the time it will start. I have had it at the Dealer and they could not find the problem. Once it starts, it will cool normally for the rest of that day even if the interior gets hot. It will fail to start again the next day until I gun the engine again.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 21, 2022, 1:42 PM

Post #2 of 10 (228 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

This should have been a very easy thing to diagnose for the dealer.

All they had to do is test for power arriving at the compressor when it wasn't working.

It sounds like what is causing it to finally engage is the additional voltage the system generates when the engine is throttled up.

There are a few possible causes for this

1) Worn clutch pulley causing excessive air gap at the compressor clutch
2) Weak clutch coil
3) Weak compressor clutch relay or corroded contacts



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



oldmots
Novice

Jul 21, 2022, 2:01 PM

Post #3 of 10 (223 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

Thanks for your ideas, I think the dealership was too lazy to let the car sit in the heat and go get it and test it. The only thing I can do myself is to replace the relay, which I will do. This car only has 52,000 miles on it, but if the relay doesn't fix it, I will get it to the shop to look at the clutch.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 21, 2022, 2:33 PM

Post #4 of 10 (211 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

You are probably right about the dealer. The techs get paid flat rate and don't have time for extensive testing.

edit: After looking at the wiring diagram I see this car doesn't use a clutch relay. The compressor is powered by Sam Control module



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Jul 21, 2022, 6:27 PM

Post #5 of 10 (198 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

Oldmots: Bummer they won't help you because it would take time to recreate this.


Try this just for exercise I guess. Wiggle wires to compressor by hand WHEN it's NOT engaging/cooling WHEN it should be. IDK but if that works like "gunning" it, I take as revving it up a lot there's a connection there that's too weak.
IF general wiring shows corrosion focus on that for a fix to last,


Tom



oldmots
Novice

Jul 21, 2022, 8:21 PM

Post #6 of 10 (186 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

I also found out there was no relay. What is the SAM Control module, I have never heard of this.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 22, 2022, 4:47 AM

Post #7 of 10 (165 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

It's what Mercedes calls the Body Control modules. It has a few of them. In this case it is also a fuse box.





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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jul 22, 2022, 4:51 AM)


oldmots
Novice

Jul 22, 2022, 7:33 PM

Post #8 of 10 (140 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

This looks like the end of the search for a guy with just a VOM!


oldmots
Novice

Jul 25, 2022, 6:30 AM

Post #9 of 10 (58 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

I do have a question, does this module with its fuses and relays have a clutch relay or is that built in somehow?


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 25, 2022, 11:54 AM

Post #10 of 10 (47 views)
Re: 2011 Mercedes E550 ac will not start up Sign In

I thought I answered that already. Everything is internal and non serviceable.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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