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#1
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kickdown switch for AC cut-out
I've got the AC working on my car now and I realize how much acceleration you lose with it on (at least from a stop). Years ago I had a Ford Probe and when you held the gas to the floor the AC compressor would cut out to give you more power. That made me think that it would be pretty easy to use the kickdown switch to do the same thing on the MB instead of having to turn off the AC when pulling out into traffic. Anyone tried this?
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1985 300D 170k |
#2
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You could put relay in the compressor control circuit, actuated by the kickdown switch.
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#3
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It'd be very easy. Tap the throttle kickdown switch, and insert a normally-closed relay right before the A/C compressor clutch (minimum 12V/5A rated). Wire the trigger for the relay to the kickdown switch.
Now, when the kickdown switch is pressed, it'll interrupt the power to the compressor clutch, the A/C will stop, and you'll get your power back.
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1983 Mercedes-Benz 240D Automatic, A/C, Power Sunroof, Power Right Side Mirror 231K Miles FOR SALE MAKE OFFER |
#4
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If you are speaking of your '85 300D, it has that ability built in from the factory.
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#5
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Jeremy,
Really? Guess I need to get out the multitester and trace some wiring cuz its not cutting off the compressor. Do you know where the relay is located off hand?
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1985 300D 170k |
#6
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OK, its the black box located on the fender well, by the firewall and the brake MC booster. So I popped it open and there is just a one-wire jumper... no control or relay of any kind. I'm assuming this is not what is supposed to be there. Can anyone tell me what should be in there?
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1985 300D 170k |
#7
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That's the Klima relay. I just replaced mine--$300+. That's why someone has bypassed it.
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1977 300d 70k--sold 08 1985 300TD 185k+ 1984 307d 126k--sold 8/03 1985 409d 65k--sold 06 1984 300SD 315k--daughter's car 1979 300SD 122k--sold 2/11 1999 Fuso FG Expedition Camper 1993 GMC Sierra 6.5 TD 4x4 1982 Bluebird Wanderlodge CAT 3208--Sold 2/13 |
#8
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does this look like the part? *************** lists it as an ac relay for $133 (but I'll give pull-a-part a shot instead)
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1985 300D 170k |
#9
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That be it. Mercedes calls it "Relay, refrigerant compressor, 001 545 74 05." It takes input from, among other things, a microswitch on the valve cover, which is switched when you floor the throttle (the kickdown switch for the transmission is in the passenger compartment, on the floor where the accelerator pedal pushes on it). This relay was made by the Klima company and so gets that name (even though they make lots of relays). Klima also talks to the temp sensors, the tach signal, and perhaps others (I forget) and "decides" whether you should be allowed to have the a/c compressor working or not. Since it is expensive (US$100+), many people simply bypass it when it fails -- my 123 had a simple relay wired in place of it. I was eventually able to find a used copy for a fair price. Sorry I don't have a spare to offer you. Caveat: other Mercedes cars have similar-looking relays (the 300E comes to mind) but they are not the same. "Accept no substitutes." Search this forum "klima" and get lots of reading material, some of it even true.
Jeremy
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
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