Repeated attempts to fix. AC will quit cooling. Will resume if the car is shut off and restarted. Somtimes will resume if temp control is put in coldest postition. What can this be? I'm told this is a big problem with this car.

try unplugging the aux water pump.located under the hood but not sure where on the SDL.these pumps are known to seize up becoming a larger than normal current draw.can affect the climate control operation.

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon

Welcome to the forum.

It's a fairly lengthy procedure to troubleshoot these systems and isolate the problem, but I can do it with you if you have patience and are a reasonably good electrical technician with a proper voltmeter.

The problem is either the CCU or the Klima relay or one of the input signals to the Klima relay.

It would be of assistance for you to have a spare "ice cube" relay. We may use it to bypass the Klima and see if the a/c will work without it.

Mine would cut the AC out after a few minutes, and it wouldn't kick back on unless I restarted the car.

My climate control head unit was bad, a rebuilt one solved the problem. Used ones are a complete waste of time and effort IMHO.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Welcome to the forum!

As Brian said you will have to do some digging on the system, but can save yourself lots of $$ fixing it yourself.

Start with the basics.

Does your tach work all the time? The Klima wont let the A/C come on if the tach is not working, thinks the engine is off.

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

I don't know much about the 603's, but seems like I heard that the models with the serpentine belt have a rotation sensor in the compressor. Belt slips, sensor doesn't sense rotation, AC shuts down until restarted. Problem could be a bad belt or tensioner.

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Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

Well since misery loves company, I am still having exactly the same problem as "Tagger".
My A/C works perfectly for between 5 mins and 30 mins then shuts off and will not restart until I switch off and re-start the engine. Then the cycle repeats itself. No sign of Belt Slippage (sound or wear) and belt and tensioner are both recent replacements. Freon charge has been checked and is OK - which makes sense since when it is working the air is ice cold.

I am about to start troubleshooting the Klima Relay and CCU. Any suggestions where to start first ?

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown

Pin #10 on the Klima relay.

If the CCU provides a ground to the Klima via pin #10, the CCU is not the culprit. If the CCU eliminates the ground and pin #10 is open........and the temperature of the cabin still demands that the compressor continue to run..........the the problem is in the CCU.

Troubleshooting the Klima is time consuming, but, it can be done. Any signal to the Klima that's not to spec will trip the relay.

Alternately, you can make a very cheap and fast ice cube relay to bypass the Klima.......but........you don't get protection in case the compressor seizes and attempts to take the belt out.

It took me a long time to figure out why mine did that. I finally figured it out when I went to check the clutch air gap. The gap was fine, but the feeler guauge came out covered with oil. The compressor seal was leaking oil onto the clutch causing it to slip, resulting in the speed sensor cutting power to the electromagnet. Cleaning the clutch mating surfaces with brake cleaner would fix it for about 10 days.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

This could be a bad suggestion...but if you have a working ac system except it turns off on you, why not bypass all the bull**** electronics that dont work anymore and hotwire the compressor with a good automotive relay 30 amp and a toggle switch on dash?

Then you could manually click on compressor whenver you wanted. Running comp continuously might freeze up the lines, Im not sure. If so, it would have to be cycled every now and then. Anyone ever do this?

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Paul
Benz-less
I need an SDL !

I second this post. BTDT.

Sixto

I've been following this thread and finally decided to register and wade in. Mine does the same thing--AC works fine around town on short drives in a wide range of rpms, then starts blowing hot air if I try to go on an extended drive, which is highly aggravating in South Louisiana in a dark car with a black interior for nine months of the year. I unplugged the aux. water pump as suggested, I replaced the CCU, I kitted the water valve and checked it for current, sprayed brake cleaner in the compressor gap, and nothing seems to make a difference although that new CCU fixed some other eccentricities. I am considering putting in a new compressor, etc. since I'm not sure when the current one was done last, but would like to explore other options such as the aforementioned KLIMA, if indeed my car has one, before giving up and throwing more money at the problem. Where do I find my klima on an 82 300D and what does it look like? Any other suggestions beyond those already mentioned most welcome. Summer is coming!

Thanks.

An 82 300D doesn't have a Klima relay as such. Check that there is a clear path between the cabin temp sensor (in the dash?) and the aspirator fan (near the blower?). I believe in that car the hose that connects these bits can disintegrate. Without the hose there may be inadequate airflow over the cabin temp sensor and thus inaccurate signals to the CCU.

As well there might be an accumulation of dust and dirt insulating the cabin temp sensor.

Sixto

Folks,

Of course there are many possible reasons. I don't know the operating temps of this situation, but I think there is an over-temp cut-off sensor for the compressor. It is located on the head. I had one go bad ( the sensor).

What are your operating temps when it shuts off? Over 100* on the gauge?

Chuck

Try unplugging the aux water pump and check results.these pumps very frequently seize=more current draw thereby affecting the climate control operation

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michael cole 1980 300SD gone now but not forgotten,87tdt,90 300te 4matic 95 e320 wagon