I just had the a/c compressor replaced in my 1999 E300TD. I posted in the diesel discussion and didn't get a response so that is why I am posting here. My old a/c compressor clutch was making a loud noise and I was replacing a lot of my belt components so I decided to replace the compressor at the same time. My old compressor was still engaging (slowly and loudly) and was blowing cold air. The mechanic who installed my new compressor called me today and said that he after he pulled a vacuum on the new system he then charged it to the correct pressure before turning the key on and turning on the a/c button so he could complete the initial charge to the correct pressure. He said that new new compressor will not engage. I have heard of some weird electrical glitch that can cause this. Does anyone have any idea what may have gone wrong, and what can be done to fix it? Thank you in advance for any advice.

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2006 E320CDI- current dd
1999 E300TD - retired
Wilmington, NC USA

Most AC systems utilize a low pressure switch that prevents the compressor from engaging if the refrigerant pressure is too low. Given that your mechanic has charged the system already I would suspect a faulty low pressure switch. Your mechanic should be able to jump across the switch - if the compressure engages, then the switch is faulty. THe other possibility is a blown fuse. I am not familiar with your model but many Mercedes after 1984 used a Klima relay that controls the electrical engagement of the compressor. Ask your mechanic if your car has such a relay.

It was working and blowing cold air, albeit a bit loud, and now is kaput? Is he a professional or a shady mechanic. Changing compressor is easy and it seems he has all the tools. Ask him how he charged the system and got all the pressure 'correct'? How could he do it without the compressor ever engaged? It does not make sense.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

The AC system can be given an initial charge without the compressor being engaged. This is a common procedure especially if the system has a low pressure (binary) switch. The low pressure switch will not allow the compressor to engage unless there is some refrigerant pressure in the system.

I don't do A/C everyday. It is not my trade but I have done enough to know what I am talking. I would doubt any professionals would charge the system to the 'correct' pressure, as per the OP, without the compressor running/engaging.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

You are correct, I also seriously doubt that the system was charged to the correct pressure without the compressor engaging. I too, would look for a new mechanic. Unfortunately, I have done a lot of AC work, and have needed to minimally pressurize the system in order for the low pressure switch to allow the compressor to engage. The danger in not doing so and getting the compressor to engage by jumping the low pressure switch without refrigerant in the system is that quite often the refrigerant also contains compressor oil to lubricate the compressor (more often than not the compressor is pre- filled with the proper amount of oil - but you never know). As I explained I am not familiar with his car and therefore suggested several possibilities including the low pressure switch, a fuse, or if so equipped, the Klima relay.

Is the EC lamp lit on the panel?

You said the pulley was noisy - you can just buy the pulley/clutch assembly and swap it out on your old one.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Thanks for all the replies. The mechanic who did the job is not shady, he is a friend of mine. He mostly works on big trucks but he gives me a really good deal on labor so I use him. I probably explained his initial charge procedure incorrectly. He did claim that the next day the compressor started right up and it has worked perfectly ever since. He told me he thinks the sensor needed to acclimate over night. I think he was to embarrassed to admit the ec button was on

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2006 E320CDI- current dd
1999 E300TD - retired
Wilmington, NC USA

210 compressor will set a code if low on freon,that code must be cleared before the compressor wiil engage to finish the charge.
You can read the a/c codes on the a/c control panel,do a search its not hard to do.


Try this http://www.eclassbenz.com/2010/02/how-to-diagnose-air-conditioning-malfunctions/ Don

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Red Green "This is only temporary,Unless it works!"

97 E300D 157000 miles
87 300TD ?141k? miles