1996 E300
New: condenser
dryer
expansion valve
evaporator
heater core
all filters
I am in the process of rebuilding the A/C system and have rebuilt the dash and now at last the climate controller on the dash is lit up like a christmas tree.

Will start to tear it all apart again ... any ideas what I missed?

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Did you read and clear codes?
http://www.mbcluster.com/Media_Diagnostics/W210%20-%20Airco%20Sensor%20Reading.jpg

http://www.mbcluster.com/Media_Diagnostics/W210%20DTC%20Codes.pdf

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CENSORED due to not family friendly words

Did you plug both plugs, securely, into the climate control?

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

The controller starts with no LED lights lit and all of the LCD displays lit. Only the fax speed buttons seem to work.

The compressor never starts.

Are there codes to clear with a ODB2 reader?

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Yes both plugs are plugged in. I have removed the unit to verify.

No, read the first link.

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CENSORED due to not family friendly words

The W210 has two CAN buses. The body bus and the power train bus. Neither of which can be read from the OBDII port.

The power train control modules (engine and transmission) use ISO 9141 protocol to the OBDII port over a dedicated wire from the ECU.

The way this car does diagnostics is each subsystem has a dedicated wire back to the 38 pin connector in the left side fuse/relay box. This can only be read with the proprietary Mercedes tools (the HHT or Xentry).

To help with the AC diagnostics there are special diagnostic modes that can be accessed by hidden menus in the AC controller. Unfortunately you may not be able to get to these because if the AC controller is locked up it won't let you get to the diagnostic mode.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thank you for your responses.

The control unit was out of the dash in the backseat for a month for this job. It got a little dusty but no damage. For 30 or 45 seconds after start up the unit has all of the LCD areas fully displayed, total gibberish, then the LED's start flashing and it is not as responsive.

Is there an appropriate cleaner or grease for the contacts on the plugs?

Do these symptoms indicate that something is not plugged in?

Are you sure the connectors are properly seated? Sure sounds like a partially inserted plug. Make sure you don't have a bent pin. Be sure the plug lever gets rotated upward as the connector is inserted and then locked into place (in the up position). The hooks on the bottom of the plug lever need to engage the posts in the sides of the CCU connector socket.

Did you confuse the left and right connectors (can't remember if they are keyed to prevent them being plugged in the wrong places, admittedly I would be surprised if MB did not key the connectors to prevent this).

Did you disconnect the battery before unplugging anything? This car is really sensitive to this and you can set codes that can only be cleared by the Xentry system.

I think you may have to find a dealer or Indy with Xentry to get on the system and see what's not communicating.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

You can pick up a can of Electronics contact cleaner at almost any auto supply store which will ensure that any grease on the contacts will be gone. Just make sure that any plug you use it on is not energized until the spray cleaner can evaporate from the surface.

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96 E300d

I have checked the connections a couple of times and they seem good.

Today the thing almost worked. The lights died down and then for a few moments the screen seemed normal with 72 degrees on both sides but still only the fan speed buttons working so I adjusted the speed down to zero and off and tried to restart the system and got only the disco light from then on.

Ordered a remanufactured controller from Mercedes. Will give that a try tomorrow. They will allow return if its not the problem.

Tried the new control unit and it worked at first, with the readout in celsius and the compressor started up, so I got out of the car and hooked up a can of coolant, got back in the car and the display started acting badly. Restarted the car and now the readout was in fahrenheit and looked good at first but would not respond and spiraled out of control to the gibberish.

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looks like a bad grounding situation here or the can going crazy.

The 2 main grounding bolts in the W210 cabin are located one near the battery behind a plastic cover (its also used as a battery disconnect sometimes) - and one is a clustered ground near the center console on the passenger side.

Remove the carpeting to find it and clean it out very good - its a layered ground so take out each eyelet and clean it.

The other point can be a faulty can service connector, it looks like a harmonica with mini plugs in it, clean that out and recheck it. I have seen one car with a wet connector doing all sorts of idiotic acts like this.

Other than that - you might want to look for pinched wiring

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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)

Installed the old control unit to test and the compressor kicked on and air was blowing out of the vents so I went back to the engine to add more coolant and when I go back to the cockpit the control unit was smoking and hot.
I disconnected the battery again and removed the old unit.
I need a wiring diagram and instruction on how to ohm out the harness.