ML550 2009, a/c troubleshooting compressor valve
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
ML550 2009, a/c troubleshooting compressor valve
Hey guys,
My a/c was not working. I found a damaged o-ring that I have replaced. System evacuated and filled with the right amount of r134a.
After this everything was good for a while. The a/c then started to work intermittent. I suspect the valve in the compressor. I have the feeling when I regularly drive the vehicle, and it is not standing for more than 10h, the valve closes.
I also checked with a scanner. Refrigerant pressure is at 5bar when the engine is off, and goes to 6,5-7 bar when the engine is running.
Pwm duty cycle 100%, evaporator temp reasonable, same as the environment.
My next step would be to measure the Pwm signal at the valve, and have a new valve ready.
Would you agree to that, or is something leading also to a failed compressor? Pressure is rising minimal when the engine is running.
Also there is no leak, 100% sure. Had a vacuum on the whole night.
Thanks!
My a/c was not working. I found a damaged o-ring that I have replaced. System evacuated and filled with the right amount of r134a.
After this everything was good for a while. The a/c then started to work intermittent. I suspect the valve in the compressor. I have the feeling when I regularly drive the vehicle, and it is not standing for more than 10h, the valve closes.
I also checked with a scanner. Refrigerant pressure is at 5bar when the engine is off, and goes to 6,5-7 bar when the engine is running.
Pwm duty cycle 100%, evaporator temp reasonable, same as the environment.
My next step would be to measure the Pwm signal at the valve, and have a new valve ready.
Would you agree to that, or is something leading also to a failed compressor? Pressure is rising minimal when the engine is running.
Also there is no leak, 100% sure. Had a vacuum on the whole night.
Thanks!
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
Maybe somebody can tell me where to check the PWM signal in the engine compartment. From above, not below the car? Is there a connector available, or straight wired from the sensor to the inside?
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
There is no fault code stored! According to the live data the pwm duty cycle should be 100%. I didn't manage to go below the car and measure it at the connector.
I appreciate any other comment like: continue to replace the valve, order directly a new compressor, sell the car...
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
On my compressor, I was also showing 100%. Replaced the valve, still not cooling. So I went under and checked the voltage - had approx. 12v with the A/C on, 0v with it off. Approximate readings since my meter is analog. My process was a little out of order, and I’m not sure how to separately diagnose the valve, but figured it wasn’t too expensive to just replace and rule it out. Ended up flushing and replacing the compressor, condenser, expansion valve, and suction side valve core. Rock auto has the old Denso compressor part number in stock right now at a good price.
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ML63 W164 A/C Relay location
Hi, can anyone tell me where the aircon compressor relay sits in the 2009 w164 ML63, I want to bypass it to see if the magnetic clutch kicks in/out. At present the a/c switch lights up but the clutch is not responsive. I am unable to recharge it because the pump won’t allow gas to get in. I checked the fuses and all are ok but can not locate the relay. Thanks
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Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
Hi, can anyone tell me where the aircon compressor relay sits in the 2009 w164 ML63, I want to bypass it to see if the magnetic clutch kicks in/out. At present the a/c switch lights up but the clutch is not responsive. I am unable to recharge it because the pump won’t allow gas to get in. I checked the fuses and all are ok but can not locate the relay. Thanks
I would use a scanner to find out.
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
On my compressor, I was also showing 100%. Replaced the valve, still not cooling. So I went under and checked the voltage - had approx. 12v with the A/C on, 0v with it off. Approximate readings since my meter is analog. My process was a little out of order, and I’m not sure how to separately diagnose the valve, but figured it wasn’t too expensive to just replace and rule it out. Ended up flushing and replacing the compressor, condenser, expansion valve, and suction side valve core. Rock auto has the old Denso compressor part number in stock right now at a good price.
How did you flush the system? Nitrogen?
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
Sorry for the late reply. I just ordered some flush from Rockauto where I bought the other parts. Bought a cheap flush canister from Amazon. One tip, since you have to remove the expansion valve to flush anyway - just plan to replace it - mine had a lot of crud in it from the compressor failure. Was better to eliminate it as a potential additional part that might be failed.
And, with the old valve in hand - drill it out and put it back in place so the you can flush out the evaporator and lines all at the same time - and collect the nasty crap in a can in the engine compartment. I didn’t do that, and when flushing the evaporator coil the nasty wash went down the firewall - has taken several washings and two weeks for the chemical smell to go away.
And, with the old valve in hand - drill it out and put it back in place so the you can flush out the evaporator and lines all at the same time - and collect the nasty crap in a can in the engine compartment. I didn’t do that, and when flushing the evaporator coil the nasty wash went down the firewall - has taken several washings and two weeks for the chemical smell to go away.
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
Sorry for the late reply. I just ordered some flush from Rockauto where I bought the other parts. Bought a cheap flush canister from Amazon. One tip, since you have to remove the expansion valve to flush anyway - just plan to replace it - mine had a lot of crud in it from the compressor failure. Was better to eliminate it as a potential additional part that might be failed.
And, with the old valve in hand - drill it out and put it back in place so the you can flush out the evaporator and lines all at the same time - and collect the nasty crap in a can in the engine compartment. I didn’t do that, and when flushing the evaporator coil the nasty wash went down the firewall - has taken several washings and two weeks for the chemical smell to go away.
And, with the old valve in hand - drill it out and put it back in place so the you can flush out the evaporator and lines all at the same time - and collect the nasty crap in a can in the engine compartment. I didn’t do that, and when flushing the evaporator coil the nasty wash went down the firewall - has taken several washings and two weeks for the chemical smell to go away.
You are amazing!!! Thanks!
Junior Member
Joined: Dec 2020
Posts: 40
Likes: 5
From: New Orleans
2010 ML550
Final unsolicited advice. I replaced all the o-rings - the pack from Rockauto has more than you need. I also wanted to replace the valve core on the suction line to eliminate potential for that to be a weak link (it has really tiny o-rings on it also.). Ordered a generic pack from Rockauto. Unfortunately, the generic ones had a different look about them and I was worried about possibly damaging the older and having to replace that line. Made the mistake of not checking it early in the process, so ended up getting one at the dealership $47 later, I’m wishing I had tried to find an OEM one online. Part number is A 000 832 08 85.
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
Hi,
final feedback: the valve was the issue. It was stucked and moved only a tiny bit. I tested it on the bench with an 12V power supply.
Getting the old out was a bit of a hazzle, I had to loosen the power steering hoses from the flange, and couldn't get them sealed anymore. So I drained this fluid as well, replaced o-rings and filled fresh fluid....
All works fine now.
Thanks to everybody! Awesome forum!
final feedback: the valve was the issue. It was stucked and moved only a tiny bit. I tested it on the bench with an 12V power supply.
Getting the old out was a bit of a hazzle, I had to loosen the power steering hoses from the flange, and couldn't get them sealed anymore. So I drained this fluid as well, replaced o-rings and filled fresh fluid....
All works fine now.
Thanks to everybody! Awesome forum!
Thread Starter
Junior Member
Joined: Aug 2021
Posts: 23
Likes: 3
From: Houston
Ml550 2009
Hi,
unfortunately I need to open this again. Here comes the thing:
The a/c was working for nearly a week now. This morning it stopped. I connected the tester iCarSoft and checked all the values. Refrigerant pressure at 10 Bar, compressor requested 100% no cool air.
I tried around a bit, and switched of the a/c, brought the engine to 2k rpm and switched back on the a/c. Then the valve seems to close and everything went back to normal.
What is your idea: Debris in the system? Voltage not sufficient to close the valve? (Voltage measured with 14,2V)
I dont know what I should do now, beside replacing all parts step by step (Which would be stupid)
Can somebody share with me a wiring diagram. I want to follow the PWM Signal from where it originated to the valve.
unfortunately I need to open this again. Here comes the thing:
The a/c was working for nearly a week now. This morning it stopped. I connected the tester iCarSoft and checked all the values. Refrigerant pressure at 10 Bar, compressor requested 100% no cool air.
I tried around a bit, and switched of the a/c, brought the engine to 2k rpm and switched back on the a/c. Then the valve seems to close and everything went back to normal.
What is your idea: Debris in the system? Voltage not sufficient to close the valve? (Voltage measured with 14,2V)
I dont know what I should do now, beside replacing all parts step by step (Which would be stupid)
Can somebody share with me a wiring diagram. I want to follow the PWM Signal from where it originated to the valve.
Last edited by TammyCutzer; Sep 3, 2021 at 11:33 AM.
