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A/C Compressor Engagement Issues
Ok. Why does the ac compressor clutch not engage on initial start or after CCU was turned off to on, until rpm's are raised above 2k??? Someone said it has to see 750 to engage. This is well above. Once engaged it stays cold inside and seems to cycle normally. It's just the initial on command that's an issue. The KLIMA has been replaced with no change. This thing is driving me nuts.
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Thanks, Mark in NC "Spark plugs?...We don't need no stinking spark plugs!" 1985 300SD "Der Silberne Schlitten" 420,000 mi Wish these were diesel: 2003 Ford Club Wagon 130,000 mi |
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On my Mercedes there must be a pressure transducer that only allows the AC pump to be engaged if the pressure is within the allowable range. If there is not enough refrigerant, it will not engage. If there is too much refrigerant, it will not engage.
I am not an expert, but my AC does work well and I service it myself.
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1991 350SD (updated rods) Biodiesel B100 when I can find it. Dino when really cold outside |
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Does engine rpm affect the refrigerant level?
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/showthread.php?threadid=10414 http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
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If the CCU in the SD models (W126) is like those in the 123 and 124 models of the mid-80s (which I am familiar with), upon startup, Klima looks at the tach signal and requires a minimum of 600 RPM for 10 seconds before it will energize the clutch. Is the car's tach working normally? If Klima doesn't get the right signal (in '84 or '85 Mercedes started running the tach signal through the EGR electronics) it won't turn on the compressor.
That's the only thing I can think of that is RPM-dependent. 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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Early 124 Klimas have a 10 second compressor delay. Heaven knows why. IIRC later Klimas are a direct replacement and don't have this delay. Maybe your 123 Klima has a similar delay. Does the compressor not engage even 10 seconds after starting the engine?
Sixto 87 300D |
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Another example of why I am glad I have a 'type one' MB AC...
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/showthread.php?threadid=10414 http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
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Quote:
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Thanks, Mark in NC "Spark plugs?...We don't need no stinking spark plugs!" 1985 300SD "Der Silberne Schlitten" 420,000 mi Wish these were diesel: 2003 Ford Club Wagon 130,000 mi |
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Hardly blame you for that lack of patience under those conditions.. the same time warp happens when people are sitting and waiting for their glowplugs to go the longer FSM time in really cold weather.. .. the 45 seconds.... that is why I always tell them to " time it with your watch '..
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1980 240d , chain elongation, cam marks reference: http://www.peachparts.com/shopforum/showthread.php?threadid=10414 http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html evap fin cleaning: http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator A/C thread http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html |
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My SDL waits 5 sec or so after starting. Probably a good idea to not load the engine down right after starting. The logic is slightly flawed though because the HVAC head cranks the blower up to high.
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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket Tesla Model 3. 205,000 miles. Been to 48 states! Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels. 2014 Cadillac ELR 2013 Fiat 500E. |
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Quote:
Sixto 87 300D |
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85 is on the flywheel only IIRC.
-J
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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket Tesla Model 3. 205,000 miles. Been to 48 states! Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels. 2014 Cadillac ELR 2013 Fiat 500E. |
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The "starter union" had it put in their contract.
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I also have one on the crank pulley IIRC. It looks to be a hall effect sensor. It also has one on the bell housing. And its the 85 W126, not a W123
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Thanks, Mark in NC "Spark plugs?...We don't need no stinking spark plugs!" 1985 300SD "Der Silberne Schlitten" 420,000 mi Wish these were diesel: 2003 Ford Club Wagon 130,000 mi |
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300SD. Starting to need reading glasses . I'm not aware of a front sensor on an 85 SD either. Are you sure it isn't the holder for the dealer rpm tool? If there are wires, where do they lead?
Sixto 87 300D |
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