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  #46  
Old 09-15-2010, 03:37 PM
sixto's Avatar
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I assume this is the 85 300D of which I know nothing. MB AC systems of this vintage typically have a refrigerant low pressure switch at the drier. It'll be the switch with contacts directly on it as opposed to the high pressure switch, if so equipped, with two pigtails. One wire at the low pressure switch comes from the PBU, the other goes to the Klima relay. Test for continuity across the pressure switch then use the wires to determine whether a signal can get from the PBU to the Klima relay. One wire should have continuity at one on the pins in the Klima socket, the other should be open across the board. The wire that's open across the board comes from the PBU. I don't know in your car whether the evaporator temp sensor is wired downstream of the PBU or one of the sensor inputs to the PBU. This should tell you whether the problem is in the cabin or under the hood.

Sixto
87 300D
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  #47  
Old 09-15-2010, 03:41 PM
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Join Date: Nov 2004
Location: Denver, CO
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Quote:
Originally Posted by sixto View Post
I assume this is the 85 300D of which I know nothing. MB AC systems of this vintage typically have a refrigerant low pressure switch at the drier. It'll be the switch with contacts directly on it as opposed to the high pressure switch, if so equipped, with two pigtails. One wire at the low pressure switch comes from the PBU, the other goes to the Klima relay. Test for continuity across the pressure switch then use the wires to determine whether a signal can get from the PBU to the Klima relay. One wire should have continuity at one on the pins in the Klima socket, the other should be open across the board. The wire that's open across the board comes from the PBU. I don't know in your car whether the evaporator temp sensor is wired downstream of the PBU or one of the sensor inputs to the PBU. This should tell you whether the problem is in the cabin or under the hood.
Sixto
87 300D
Yes, this is for the '85 300D - wow... this ought to keep me busy for days... thx sixto - I'll give this a try and do some tracking.
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  #48  
Old 09-15-2010, 11:11 PM
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Success...

I got lucky - tonight I drove down to my friend's house. He evacuated the system, pulled the vacuum, recharged it with fresh 134a and we started testing.

Right away I noticed a difference - I started getting voltage at the compressor plug right away. I knew this was a good sign.

We ran the car, clicked the A/C on and sure enough it started to cool and it kept getting cooler and cooler. We continued to recharge the system. It seems to be working great now.

This makes me soooooo happy: Yippie, yahoo, yeah!

Very satisfying. Thanks all for all your suggestions and guidance.

James
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1987 Mercedes 300SDL; SOLD
1985 Mercedes 300D; SOLD
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1995 Toyota Land Cruiser - 3X locked; 182K
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