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AC compressor has no power

Tiny
JAMIE LOPEZ
  • MEMBER
  • 2003 MERCEDES BENZ SL500
  • 5.0L
  • V8
  • RWD
  • AUTOMATIC
  • 109,507 MILES
Vehicle has a new AC compressor, pressure/temperature switch, is full of crown (2.09lbs), but still has no power to compressor. Check all fuses under hood, all okay. Checked wires from switch to connector m15, all okay, but no 5 volts reference or no.8v to 1.8v on the other three wires. I cannot find any kind of wiring diagram for this car, AC or other wise. Please help me figure out this nightmare. Thanks in advance.
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Tuesday, October 18th, 2016 AT 2:03 PM

13 Replies

Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
Have you checked and cleared the codes in the HVAC module? If there are any stored codes from the original failure they will inhibit the compressor until cleared.
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Tuesday, October 18th, 2016 AT 3:36 PM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
Yes, all codes are cleared, still no power at compressor.
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Tuesday, October 18th, 2016 AT 4:01 PM
Tiny
WRENCHTECH
  • MECHANIC
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I am not talking about engine codes. I am talking about codes specifically in the HVAC module that can only be access with a very high grade scan tool. If it is resetting any codes, then follow up on that. Other than that it going to be following a wiring diagram by an electrical technician.
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Tuesday, October 18th, 2016 AT 5:03 PM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
I have a high grade scan tool, a Matco Maximus 2.0A, so yes all codes are clear! I have already check the wiring from the left Sam module to the switch and to the compressor, but for some reason I cannot find and electrical diagrams for this car. Do you know of a website that I can access to get these? As you know that tracing done a electrical problem with a diagram is almost impossible.
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Tuesday, October 18th, 2016 AT 6:50 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
I do not know if you have ever tried to follow Mercedes diagrams, but it is not easy.

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294525.jpg

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294526.jpg

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294527.jpg

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294528.jpg

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294529.jpg

http://i1198.photobucket.com/albums/aa448/Wrenchtech/176294530.gif

https://www.2carpros.com/images/external/176294531.gif
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Tuesday, October 18th, 2016 AT 7:01 PM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
Yes I have and you are right they are very hard to follow, but these diagrams are what I have been looking for! Thanks so much! I will let you know what I find. By the way you wouldn't have any idea or guess at what it might be?
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Tuesday, October 18th, 2016 AT 7:28 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
Pressure switches and relays are the most common areas of failure.
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Wednesday, October 19th, 2016 AT 2:33 AM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
Can you possibly post a picture where the AC fuses and relays are? Thanks in advance
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Wednesday, October 19th, 2016 AT 7:43 AM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
In relation to where they sit in the fuse block.
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Wednesday, October 19th, 2016 AT 7:47 AM
Tiny
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It is less work to just test all of them then research which ones are which and location.
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Wednesday, October 19th, 2016 AT 7:58 AM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
Okay, thanks.
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Wednesday, October 19th, 2016 AT 8:32 AM
Tiny
JAMIE LOPEZ
  • MEMBER
  • 8 POSTS
Ok, I've check all fuse and relays, all are good, checked power and ground at the acc module, all good, checked for signal coming out of acc when ac power button is push, signal is good, could it possibly be the left sam/fuse block?
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Friday, October 21st, 2016 AT 7:46 AM
Tiny
WRENCHTECH
  • MECHANIC
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That's what the wiring diagram is for. You need to print that all out, tape all the sections together and mark all the components. I can't tell you much more about the circuit. If you have a high grade scan tool you can read each SAM and see what is going on.
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Friday, October 21st, 2016 AT 8:59 AM

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