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2003 MB ML350
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Discussion Starter · #1 ·
A few years ago my AC compressor had a catastrophic failure.
I ordered a compressor, dryer, and expansion valve.
I had a shop remove the refrigerant.
I replaced the compressor and dryer.
I noticed the expansion valve turned out to be the wrong part after replacing the compressor and dryer and decided to proceed without replacing the valve :/
I also couldn't determine how much oil to leave in the compressor since my old one threw it's oil everywhere :/
I left all the oil in the new compressor.
I had a shop vacuum the system and charge it.
It worked great for a while, but then started going out from time to time.
It got progressively worse as it would come on and off without anything to relate it to.
I took it back to the shop to have it checked, but ML350 wouldn't misbehave for them.
As I had another vehicle to drive, I mainly only drove the ML during the cooler months.
I am getting back to work on it, and bought a manifold and vacuum pump.
They system is blowing ambient temps all the time now, at idle or on the interstate.
The front two fans aren't running at any time.
I've checked all fuses in the passenger kick panel and under the hood.
Checking the blower flap motor, I can hear it move and feel the heat from the vents when moving the temperature knob to high.
The high and low lines continuously feel ambient to the rest of the engine compartment throughout testing.
Static pressure is about 100 psi on both low and high with ambient temps of about 85 F.
Pressure and vent temperature doesn't change after letting the system run for 10-20 minutes with the blower on high, recirculation turned on, temperature set to lowest point, and vehicle at idle.
Checking this forum, I've removed the AAC and didn't find any scorched circuit board traces or anything abnormal on the board.
With this clutch-less compressor, I guess I'm left checking for 12v on the compressor and then tracing that pink wire back through the fuse box to the AAC.
I've read some variety of things about the pressure switch, so I guess I'll also check for 5v there.
I also read about checking the coolant circulation pump, so I'll check that as well.
I'm concerned that the system wasn't completely cleaned out and debris has clogged the expansion valve open or closed, but from what I understand, neither situation would explain the test results I'm getting.
I'll proceed with tracing the pink wire from the compressor to the AAC, checking the coolant circulation pump, and the pressure switch.
If anyone has any other suggestions or can provide some kind of logic on everything that can disengage the compressor, I'd appreciate it.
 

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Dallas, Texas
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Do you have a scanner that will read faults and actual values from AAC? There is single wire just behind oil filter that leads to compressor control valve. If you have clamp on amp meter measure current.

With engine running take a look at center hex on compressor. Is it spinning?


 

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2003 MB ML350
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Discussion Starter · #3 ·
I don't believe my cheap scanner can. Here is a link to the Amazon page of the one I bought, but that was in 2014. It looks like it may have changed since then.


I did see the scanner you recommended, the Autel AP200M, for $60 on Amazon. I've been considering getting something better and have been looking at Autel's products. I'd like something that can also access ABS, Airbag, and maybe more, so I was considering the Autel AP200 for $10 more, but I still need to look deeper into scanners.


I have a hook meter, but it's not very sensitive, so it didn't pick up anything. I believe I have a clamp meter somewhere I can dig up. I did trace that wire back to the compressor, and I found that plug mentioned in one of your links. Before reading that first link, I figured those wires were the ones I was looking for. I'll check it for 12v.

Oh, and the center nut on the compressor is spinning along with the entire ... pulley? I'm not sure what to call it since I have the clutch-less style compressor.
 

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Get AP200M it will read codes and live data from every W163 module. No coding or component activation.

Signal going to compressor is 12V PWM 100-800 mA.

If center hex is not spinning that means torque limiter broke loose to protect drive belt. That's not your problem.
Fault in pressure/temperature sensor will keep compressor from being activated.
 

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2003 MB ML350
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Discussion Starter · #5 ·
Doh! Neither my hook meter or clamp meter have DC current modes :/

I didn't get 12v at that connector with the AC on. It actually tested ground.

I tested the #1 pink wire on the terminal block on the passenger side of the AAC. I got 12v with the AC on and 6v when fan speed was turned all the way down or the AC button was pressed.
I traced it to the fuse box, which looked like it was right next to the pink wire that goes to the compressor like my wire diagram indicates, but it started to rain so my troubleshooting has come to a halt.

Well I guess I can check out scanners now and maybe clamp meters with good DC current sensitivity.

BTW thanks so much for all the help so far. I tried to disconnect that pressure switch to test, but it's fighting me :/

I at least feel like I'm narrowing this issue down.
 

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Discussion Starter · #6 ·
Everything on the front of the compressor, center bolt to the belt contacting portion of the pulley, is spinning with the belt.

I tested the pressure switch on pink, which looked tan and on terminal #2, and on tan, which looked brown and on terminal #1. I first got 5v with ignition on along with the front fans coming on, but I forgot I had several connectors disconnected. After reconnecting everything, I got 5v at all times, ignition on or off, and no front fan action.

2701365


I tried removing that pink wire and purple wire to do an inline current measurement, but I can't get the wires out of the connectors :/

I've traced the pink signal wire from the AAC to a blue wire in that same large connector in the fuse box, which I'm figuring goes to the compressor. I can't seem to get that connector with the blue wire off at the compressor to test though.

I'm guessing at this point, I really need to get a scan tool to clear anything in the AAC (thanks to my genius idea of turning on the ignition with multiple connectors disconnected.). I'd like to buy something that works on all my cars and various control modules (ABS, Airbag). I was considering BlueDriver, as I'm not crazy about subscriptions, or the Auxtel AP200 since it supposed to support ABS and airbag control modules versus the AP200M.

I'm also curious if I should just take the SUV by a shop to get the refrigerant recovered to see if I'm low with my ultraviolet pen light and accompanying yellow goggles, but I didn't see anything.
 

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AP200M reads all modules in any MB I connected it to.
 

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Discussion Starter · #9 ·
I managed to get the connector off the compressor, which had a blue wire.
It showed 5v when off, 9v with engine on and AC off, and 13v with engine on and AC on.
Of course that's only half the story, and I found some clamp meters for $40 that may be accurate enough.
I'd rather buy more toys, er, tools ;)
Speaking of which, I'm also going to get that Autel AP200M. I don't want to take any chances with something else not being able to communicate with the AAC.
 

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Discussion Starter · #10 ·
My new toys came in. I'm getting 700 milliamps with the AC on after zeroing. I also had a ton of codes in my AAC that's like from me forgetting that I had stuff unplugged while turning the car on, so I cleared the codes. I'm going to let it run and get more familiar with this new scanner and it's software. I've got my wife's Lexus IS300's AC to also troubleshoot in the mean time. Oh and did I mention the AC system for the second floor of my house is blowing warm too? sigh
 

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Discussion Starter · #11 ·
Reading over this and other posts, it's looks like my compressor is engaging, but with equivalent pressure on both sides, I'm figuring either the expansion valve is wide open or the compressor is bad.

Funny because it looks like my Lexus is doing the same exact thing, equivalent 100 psi pressures on both side with a running compressor. The wife is saying she'd rather get rid of them as is and try to get something without issues just so I can have my weekends back. I'd rather sell a car without issues, unless it's going to someone that knows how to work on cars.
 

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Reading over this and other posts, it's looks like my compressor is engaging, but with equivalent pressure on both sides, I'm figuring either the expansion valve is wide open or the compressor is bad.
Expansion valve has small metering orifice that even when it is stuck open there will be significant pressure difference. 160/60 hi/lo.
Your compressor control valve is stuck and not reacting to current applied. Or compressor shaft sheered internally.

 

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Discussion Starter · #13 ·
I figured there'd still be a pressure difference, but I haven't found anything to reinforce that. I think I read somewhere that equalized pressures could mean an open expansion valve. Thus that incorrect thought has been bouncing around my head.

Well it sounds like my options are to replace the compressor, rebuild the compressor, or forget the whole thing. My wife is wanting me to forget the whole thing and get rid of the car. I'm curious to see if I can rebuild it. I have a vacuum pump, so I'm guessing I need a tank next to recover the refrigerant. I'll have to research that. Considering compressors are $400, and I likely need to get two (one for the Lexus), it sound like a good investment to me. I already have a kitchen digital scale to measure refrigerant.

Witek_M, I really appreciate all your help on this. I'm regretting not posting other stuff on this forum now. I've been able to figure out most of the issues with this SUV on my own, but I have had to guess on one electronic issue before. I prefer to research, learn, diagnose, and save money than guess and possibly waste money, so thank you so much for your advice and time!
 

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Compressor is Denso 7SEU16 type. Denso number specific to MB is 471-1474.
Here is one on Amazon.

Here is control valve for it. Ebay listing shows that it fits 7SEU16. I am not sure. Never done it. If you feel lucky go with that.
 

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I have had very good luck with the Denso purchases made on Amazon.
Got one most recently for the ML320 and the replacement went well.
Used a friends Robinaire to vacuum down and then charge the system.
 

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Discussion Starter · #16 ·
That Denso compressor Witek_M linked is exactly the compressor I bought, I had intermittent problems with it right away, and now looks it to be the issue entirely.
 

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99 ML430, 00 ML320, 05 E500 4matic Wagon
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Mine came with a big sticker on saying it was pre oiled and it was.
I installed it, a new drier with oil added to the drier. Ten minutes later
it was on the AC machine going through the complete charge cycle.
Did you fill it on an AC machine or use suicide cans to fill it? Also
did you add oil? Was it vacuumed down?
Sorry for the questions, but failure of these Denso units so early
is almost unheard of.
 

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When compressor grenades stuff goes up suction line. Unless very thoroughly flushed it makes it back to the compressor.


 

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Discussion Starter · #19 ·
@Noodles I took the vehicle to a shop to with an AC machine.
Oil came with the compressor, and I left all of it in.
The system was vacuumed down.
To Witek_M's point, I certainly wouldn't rule out debris being the true culprit.
I had requested the system be flushed and told the shop how the compressor experienced a catastrophic failure, but I'm not sure how well it was flushed.
 

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Thanks for the clarification.
I reread your first post and should have
realized then what steps were done.
It is hard to know how the shop did the final
steps. I did flush mine so I know it was done.
I do believe that debris may have been the
culprit.
 
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