mebugayan

Hello, new to the forum, thank you for all info.

I got a 2004 ML500, absolutely love it. I am having an issue with the AC. It seems like multiple things could be going wrong. Not sure.

1) I do not hear a clicking sound when I turn the AC on. Relay is good, swapped it with the windshield water pump relay, works.
But, I do not have an about 13V ready at 2 of the relay plugs like I would have for the windshield water pump relay plugs. Could be a reverse logic thing, but still I think I should have a 13V sitting on 2 of the plugs.
2) I looked at the compressor, I have read about the bolt in the middle in the forum, looked for it whether the bolt starts turning with the AC turned on. Well mine turns immediately when I start the car. It actually does not have a bolt, looks like the tip of a hex/allen wrench.

I could not recharge the system, because it probably had no pressure, which would be the case if the compressor was not working, correct?
So lets say I have a faulty compressor, why don't I see the 13V at the relay plugs? I am guessing because of some fault, so the system does not let the relay have it, I don't know?

Also, ML500, I believe does not have a fuse for AC, ML320's do. Correct me if I am wrong.
Thanks in advance!

Maj. Dundee

There is no relay for the A/C Compressor. Power to the compressor is supplied from the AAC Control Module by way of fuse #5 in the right side kick panel fuse box.

mebugayan

Thanks. I checked the fuse, it is good. I guess I could take the fuse out and check voltage across terminals when the AC is turned on, right?

Maj. Dundee

Yes.

mebugayan

Fuse 5 takes the whole instrument control unit out, so I couldn't check the AC by it self.
I took the vehicle to get an AC recharge, Evacuated and recharged no difference.
The mechanic hooked up the mercedes diagnose tool. Couln't find the fault.

At this point I think I got an issue with the compressor. No rpm changes when the AC is enabled or disabled. I do not see a clutch movement, maybe mine doesn't have a clutch.
How to check a compressor?
Thanks.

Maj. Dundee

There is no outside clutch, it is internally activated.

You must now check the PINK wire that activates the compressor. With the key out of the ign.,remove both covers on the eng. compartment fuse relay box.

Then remove the three screws and pull the fuse/relay module out of the fuse box. Flip it over onto a towel to expose the underside.

Turn the key to pos. #2 and locate the small blower motor and feel it to see that it is running. Is it?

Start the eng. and select A/C. Then locate connector C-F wire #8 PINK and connector MR-E wire #7 PINK.

Test metal contact at #8 wire for 12v and then contact #7 for 12v. Is there 12v at both?

mebugayan

I turned the A/C ON. I tested the terminals C/F #8, MR/E #7. Connectors are plugged in, tested from the crimped metals of the wires, neither of them have the 12V.
I tried to feel the tube on the first picture. It does not feel like activated when ignition is in 2nd position.
What does this show?
Thank you.

Maj. Dundee

I left one thing out that causes this problem.

The next thing to check is the Coolant Circulation Pump. eng. not running, turn the key to pos. #2 and feel with your hand. Does it run?

Feel the pump with your hand and see that it is running. If it is not, it must be replaced along with the E-box blower fan.

Maj. Dundee

M/B made a huge mistake by wiring that small motor/fan with the AAC Cont. Module. Once the motor shorts out, it damages the the circuit board in the AAC and prevents the compressor actuation.

This now means that you must replace the E-box fan and the AAC Control Mod., used will work fine. See photos of the AAC and damaged circuit. Before you start you must have a few tools to do it, so read the PDFs and make sure you have them before starting.

The next step is to remove the AAC Module, take it apart and check the circuit board.

Maj. Dundee

Please stop posting on two separate forums.

mebugayan

What other symptoms would I get if the AAC circuit board is damaged? I am asking because everything else seems to work fine.

Can I provide 12V to the EBox fan and test if it is actually shorted out?

The other thing is, the mechanic supposedly charged the AC, could he charge the AC if the compressor was not actuated?

Thank you.

Maj. Dundee

The only symptom is the loss of the compressor.


And yes, you can recharge the system without the compressor working.

No on the E-box fan, just leave it alone for the time being.

Did you check the pump yet, it takes 10 secs.?

mebugayan

The coolant circulation pump. It ran the very first time this morning, ignition at pos. 2. I tried again, second time, it did not run.

Maj. Dundee

Try it again in the morning, cold start. Leave it running for at least 2 mins.

mebugayan

Tried again this morning, the circulation pump did not run.

Maj. Dundee

Did you remove the AAC to check if the circuit board is burned?

mebugayan

I do not have the tools yet. Is there anything else I should check?
What do you think of the coolant pump?

Maj. Dundee

First check fuse #5 in the right side kick panel fuse box to see if it is blown. If it is, replace it and try A/C. If it is not blown, proceed with instructions below.

Buy this Bosch pump, which is for a VW, 1/2 price of M/.B one and it is exactly the same as the M/B, except for the top cap.

Remove your old pump and remove the 4 screws and the top cap. Then do the same for the new one and put the old cap on the new pump as the size is slightly different

After you do the repair, do not attach the electrical connector until you have replaced the AAM.

slagdemon

How do you charge an AC system without a working compressor? You'd never get a low pressure side and the system wouldn't pressurize accurately enough to put anything in it. If you pulled a vaccum first, let it sit for 30-60 minutes, then hooked up a can of refrigerant, some would go in, yes, but you'd never get an accurate fill without a working compressor and anyone who has filled an AC system would know something was wrong.

Maj. Dundee

Barring any electrical problem which prevents the compressor from working or any other component failure , It is not necessary or required that the compressor be running to accept refrigerant.

No one suggested that single can recharge be used. Evac and recharge machine is always required.

Even after using the correct procedure, previously stored code/s in the AAC Control Module will prevent the compressor from operating.

Dryrotted

Maj. Dundee I have a similar problem on a 2004 ML350. C
an we work off this thread or do you want a new post in W163?

Maj. Dundee

New post and describe your problem. You must scan for codes.in AAC control module.