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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4487
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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Ml450: ML 450 AC 1999 no power to compressor, refrigerant checks

Customer Question

ML 450 AC 1999 no power to compressor, refrigerant checks out great. It works every once in a blue moon and is very cold. The switch lights up but no AC
Submitted: 2 years ago.
Category: Mercedes
Expert:  Lou P. master tech replied 2 years ago.
Hello my name is ***** ***** i will do my best to help you , i strive for EXCELLENT service and nothing less.when you say switch do you mean you replaced the AC control panel ? Or what switch are you talking about ?
Customer: replied 2 years ago.
We have changed the air conditioner control panel switch inside the car.
Customer: replied 2 years ago.
Hello...compressor not locked up!
Customer: replied 2 years ago.
Hello are you still there?
Customer: replied 2 years ago.
Hello I would love to get an answer :) it is 95 degrees here, and my car is black 😂
Expert:  Lou P. master tech replied 2 years ago.
Sorry for the delay I was commuting from work to home. The AC compressor is controlled by the AAM (all activity module ) a pink wire to the conpressor. Sometimes the compressor wire gets pinched between the power steering pump bracket and the engine. Check to make sure the wire is free moving and not pinched.
Customer: replied 2 years ago.
No worries I was just afraid my phone was messed up also:-/ hold on let me locate that wire.
Customer: replied 2 years ago.
Found the wire but that doesn't seem to be the problem. No power on the pink wire going to the compressor
Expert:  Lou P. master tech replied 2 years ago.
Ok I had a Ml one time that had a burned solder inside the control head. Did you replace the whole control head or just the AC switch portion ? I can't remember if they can be replace separately it's been awhile
Expert:  Lou P. master tech replied 2 years ago.
I couldn't tell yet from the wiring diagram but there should also be a relay in the fuse box. I won't have access till tomorrow again in the am to my diagrams I quickly looked at the diagram to tell that the AAM controls the compressor and the color of wire.
Customer: replied 2 years ago.
Re palaced the entire switch the fuse has been replaced also but the solder makes sense! My husband a mechanic himself wants to know if you know a way to jump across the switch to determine if he maybe had 2 bad switches
Expert:  Lou P. master tech replied 2 years ago.
Yes , I can give him some ways to test the AC control panel , but it won't be until tomorrow morning if that's ok. I can try to tonight but not 100% sure I can. If this is not acceptable let me know and I will opt out to see if another expert can help.
Customer: replied 2 years ago.
Would it be easier if you talked to him on the phone?
Customer: replied 2 years ago.
I'm so sick of not being able to drive my car because of the heat... I decided to do something myself. Haha
Expert:  Lou P. master tech replied 2 years ago.
If need be we can switch to a phone chat , but fixing this should be easy (fingers crossed ) I'll try and get some info uploaded tonight for you
Customer: replied 2 years ago.
Thank you, ***** ***** says if he had a wiring diagram for the AC he could figure it out . He's a Mopar man and hates my car haha but I love it! Thanks for any help you might give
Expert:  Lou P. master tech replied 2 years ago.
My brother in law has a sweet 71 cuda' not to get off topic, and out wiring diagrams are not like the typical. I can definitely send what I would reference that way he can see what I am looking at for sure. I will do my best , I have a good percentage of fixed over the Internet scenarios lol.
Customer: replied 2 years ago.
Well my husband would love to talk about the '71! But the ML that's a mother story. Thanks for any help or ideas you may have we are not at work all day but Eddie (my husband ) will be Abe to converse back and forth with you today. Thanks in advance, I think the high today here is 95 ! Haha
Expert:  Lou P. master tech replied 2 years ago.
ok im here now gathering the info
Expert:  Lou P. master tech replied 2 years ago.
all of the years are different so i need to make sure of the date on the sticker on your door, it will have the vin and tell the month and year the car was made.
Customer: replied 2 years ago.
ML###-##-####
Expert:  Lou P. master tech replied 2 years ago.
ok thanks
Expert:  Lou P. master tech replied 2 years ago.
what i am going to send you is a diagram, a legend and a diagnosis sheet. the legend will tell you what all the numbers mean (numbers near the boxes are parts designations) all modules are labeled with a "N" solenoids with a "S" and motors with a "M" so if you have any questions let me know these are not like typical diagrams. and the diagnosis will tell you what the pins at the connector and pin number should show when tested.
Expert:  Lou P. master tech replied 2 years ago.
ok apparently this one does not have a diagnosis sheet. not a huge deal. the N10 is the AAM(all activity module) its snapped onto the bottom of the fuse box in the engine bay.here are the links take a look at them and let me know if you understand and can interpret them, that way we can be on the same page, and let me know if its the hubby or the wife lol. just to make sure nothing gets lost in translation.
Customer: replied 2 years ago.
This is Eddie and I will try this when I get home I wish it was on my C USA they were simple plus I could let the top down
Expert:  Lou P. master tech replied 2 years ago.
the diagram shows a scale also, letters up and down on the sides and numbers on the bottom, so i will use these to help us stay on the same page. so at the bottom near number 21 , there is the heater module (s98) , inside there is (S3) which is the ac on switch, so if that switch is on then on connector 2 pin F is a TAN wire that should have power when the switch is pressed. ( the boxes on all the items show a big number (connector number) and letters (pin designations) to assist in diagnosis) so with that being said, remove the ac panel and check the tan wire for power and when the compressor is not engaging see if the tan wire has power. the tan wire is KEY. it goes from the ac head unit to a ac control module, then from the ac control module its pin 4 (orange wire) location 35 at top of page (N19) then to the AAM. so we need to establish first that the power wire is getting power from the ac head unit to the module. hope this helps.Please take a second and click the box and rate my service GOOD OR EXCELLENT SERVICE if you feel I have been helpful and please request me in the future. If you feel I have not been helpful please DO NOT RATE BAD OR POOR AND WASTE YOUR MONEY , I will opt out to see if another expert can provide more or better assistance so you're not wasting your money!!. Thanks for choosing just answer. Lou. also , if you feel i deserve one , BONUSES are GREATLY APPRECIATED ! 😉Keep in mind that rating me does not end the chat, it simply credits me for assisting, i will still be here to help if follow up information is needed , Lou. i will stick with you until we come to a conclusion or until we run into a issue that absolutely needs a scan tool to proceed.
Expert:  Lou P. master tech replied 2 years ago.
Hello, Eddie, just let me know, this tan wire test should hopefully end well without needed to go further, these systems on the ML are barbaric and generic so they are the easiest to diagnose without a scan tool.
Customer: replied 2 years ago.
I do not have power on the tan wire what should I do to get it to there
Customer: replied 2 years ago.
Also when I unplugged the switch the heater started blowing good and hot
Expert:  Lou P. master tech replied 2 years ago.
That should be default for the full heat. Ok if no power on tan wire with it connected to the AC panel then the AC panel sounds to be the issue , if the AC light is on the tan wire should have power
Customer: replied 2 years ago.
The switch lights up but no power out the back is there a way to jump power there to make to compressor come on or will it send power to another relay like the heat default
Customer: replied 2 years ago.
I have another control box that I am going to pick up and see if another box will get me power to the tan wire
Expert:  Lou P. master tech replied 2 years ago.
Ok sorry for the delay man , I'm commuting at the moment I'll be back in about 20. If you can take the unit apart you can trace the pins to a circuit board and solder joint if i remember correctly
Customer: replied 2 years ago.
I changed the control box still no power on the number 4 pin but I have power to the E pin
Expert:  Lou P. master tech replied 2 years ago.
Ok at the moment I will have to opt out , I have a personal emergency that popped up and I do not want to keep you from progress. Sorry. I will check back tomorrow if no one has helped. My apologies. Lou
Customer: replied 2 years ago.
Oh no get me another tech on the line! You have my money sorry for your emergency but like I said its 95 degrees here!
Customer: replied 2 years ago.
We have been ruling out things all day I need some expert advice!!!
Customer: replied 2 years ago.
Hello I need help with my AC first thing in the AM please. Thanks
Customer: replied 2 years ago.
Hello! I need someone to help me figure out my air situation! It's been 48 hours!!!
Customer: replied 2 years ago.
Sad that you say you will help, and then leave me hanging with out air!
Expert:  Lou P. master tech replied 2 years ago.
Sorry I had just seen your replies , not sure why no one else had helped. Have you made any progress ?
Customer: replied 2 years ago.
No Progress, eliminated every option we could think of. Still no power to the control head switch has power. I'm at a loss
Customer: replied 2 years ago.
We worked on it all day Saturday 😩
Expert:  Lou P. master tech replied 2 years ago.
Ok providing you don't rate me negative for having a family issue arise I can opt back in and try to help you figure this out if that's ok with you ?
Customer: replied 2 years ago.
Sure I just want my air to work, I'm not mad with you, up set because 96!hours late and no response. I would appreciate any help you might give
Customer: replied 2 years ago.
I will give you a great rating if I can get air in the car I love :)
Expert:  Lou P. master tech replied 2 years ago.
I'm guessing others seen this chat and steered clear from the hard diagnosis. Ok so let me opt in and see what we can do.
Customer: replied 2 years ago.
Thanks
Expert:  Lou P. master tech replied 2 years ago.
How do you know the refrigerant is full let's start there
Customer: replied 2 years ago.
I put a set of gauges on it
Customer: replied 2 years ago.
Also when it come on it was blowing cold
Expert:  Lou P. master tech replied 2 years ago.
Ok what pressures did the gauges read ?
Customer: replied 2 years ago.
I don trembler the exact number but I know the level was good also my brother is a ase ford tech he also saw the gauges were good
Expert:  Lou P. master tech replied 2 years ago.
Ok fair enough. So at this point when is the last time the ac worked ?
Customer: replied 2 years ago.
It worked two weeks ago for about fifteen minutes after I pulled the control switch out and put it back in
Expert:  Lou P. master tech replied 2 years ago.
Ok so let's start at the compressor. Can you unplug the compressor and turn the ac on and check for power at the connector ? If you can't do tonight that ok I will check back in the morning also , I'm not leaving you im just saying that I will also be on in the morning.
Here's what I want to do.
Expert:  Lou P. master tech replied 2 years ago.
Turn the ac on like normal , switch pressed with the light on , then check for power at the compressor wire , if power then compressor is bad , if no power we need to access the intermediate connector x22 on the diagram that should be under the fuse box/AAM just follow the same color wire from the compressor then check for power at that connector , if power then the wire is broken between the connector and the compressor if no power then need to make sure the connection is good at the fuse box /AAM ON connector M/A PIN number 2.
Expert:  Lou P. master tech replied 2 years ago.
Per the diagram the wire from the compressor is brown with a violet stripe up until the connector x22 then it's pink up to the M/A connector pin 2 on the bottom of the fuse box.
Expert:  Lou P. master tech replied 2 years ago.
If there ends up being no power up to the fuse box you need to separate the AAM from the fuse box and make sure there's resistance or continuity from the M/A connector pin 2 to the 28th pin where the AAM snaps onto the fuse box. Please take a second to read through what I said and review the diagram so we are on the same page.
Expert:  Lou P. master tech replied 2 years ago.
The compressor is labeled a9 on the diagram just above the 13/14 numbers on the bottom row
Customer: replied 2 years ago.
I checked the wire from the compressor to the ma connector it is good how does the Adam come loose so I can check the 28 th pin
Expert:  Lou P. master tech replied 2 years ago.
It snaps on and off you will see a single release hook and a few tabs to depress if memory serves me. So you will need like 2 or 3 small flathead screwdrivers and maybe a second pair of hands. Was there power on the compressor line ?
Customer: replied 2 years ago.
I just checked continuity and it was good on that pin
Customer: replied 2 years ago.
Is there a way to check from the relay side of the fuse panel to see if there is power the board did not want to split apart but nothing looks burnt
Expert:  Lou P. master tech replied 2 years ago.
Ok let's make sure we are on the same page. Take the front fuse block assembly out of the big black plastic housing and when you turn the fuse block upside down the AAM is the module the is snapped into the side with more connectors and a black antenna wire also. Also I have taken my time to answer your question the best i could and i will continue to help if you need follow up information , all i ask is that you PLEASE take a second to rate my service so i may recieve my credit for assisting you. Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information until we get to a point that may require other outside help. I understand we have not completed your repair yet but we experts do not get paid until rated and a problem like this I would have normally charged 200$ for at the shop since you can see the difficulty in the diagnosis. And the time I spend with this inhibits me from helping other customers which does affect me. Hope you understand.

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