On my 89 420SEL with 150K miles, the AC comes and goes, the local guy says the freon is OK and it's the fan clutch, I read on this board that the thermostat might be bad causing the fan clutch not to work.
The electric cooling fan comes on with in 30 seconds after the engine is started cold, but the engine does not run hot, the temp gauge is always normal. The car is run very little, 100 miles / two weeks.

Fan clutch is $250, thermostat is $30.

The local shop owner is a great guy! If there is something the car owner can fix on the car himself, he suggest do it yourself, or he can repair it for a fee. But if it's not too labor intensive he explains the process.

My 89 420 SEL started having AC problems. sometimes when I started it the AC works fine, the next start no AC, for about a week. I figured low freon, but the shop owner says the AC freon is OK, and said he thinks the fan clutch is bad and that I can change it myself. When I check on the price it's $550 from MB and around $250 for aftermarket. He said the fan ran on after the motor was cut off. And without the fan clutch spinning the AC was cutting off.

Then I checked this board and found some posts saying the "Thermostat might be bad" resulting in the fan clutch switch might not be working properly, and the electric fan running too much.

The thermostat is a cheaper start in the fix than the fan clutch.

I'm not sure the fan clutch has anything to do with the a/c cutting off.

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Jim

The shop owner said the fan clutch spun after the engine stopped after checking the freon in my 89 420. He said the engine was probably getting warmer than normal due to the fan clutch weakness since it did not stop turning when the engine stopped. Said the engine was hotter so the AC switch was cutting off the compressor.

The electric fan comes on within 30 seconds of starting the engine. usually it would only run if the engine was hot.

You should be able to see this on the temp gauge. If it stays above 100dC then yes it is a little warmer than normal.

I don't think so.

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Jim

Also, I don't see how the thermostat could cause a problem with the fan clutch.

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2012 E350
2006 Callaway SC560

I read this on a post here where advise was given about AC problems.

If the theromostat is failing the car would run hotter, and the AC switch would cut off the compressor, resulting in no AC.

This information was an older post in the search part of this forum.

Thanks for all information, I don't want to replace the fan clutch ,and spend around $300 if the thermostat could be a problem. $30 is a lot easier to spend than $300 when you are retired. I can fix almost anything, once I know the details.

The book manuals for MB are not there like Chiltons where exploded images really help. I bought the MB CD and it's good but it's not great.

Give me a technical book with pictures and I can repair it. I grew up with exploded diagrams views, it's had to find anything like that for Mercedes.

OK, what does the temp gauge read? Should generally be 80 - 100 C.

Is your car running hot?

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2012 E350
2006 Callaway SC560

Today we ran the car about three hours here in south Louisiana. the outside air temp is right at 100 degrees. The AC in the 420 worked but did not freeze you like it used to do. \

The temp gauge varied from about 90-100C, and the electric fan at the grill ran all the time. the electric fan at the grill never cuts off runs as far as I can tell runs constantly.

Thanks to all for any help

AC on My 89 300se had intermitent problems cooling. Turned out the belt tensioner was bad. My mechanic said the slipping belt caused the sensor to shut down the AC compressor. I also read on the board that sometimes oil on the belt would also cause the belt to slip resulting in AC not working

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RH

16 GLC300
12 C250
98 E300D
89 300SE
84 300SD sold

I don't think you need a fan clutch with those temperatures/conditions. 100dC on the coolant temp indicator should not shut off the a/c. The fan in front of the condenser is running has all to do with the a/c system and not much to do with the engine cooling system.

Why don't you connect some gauges to the a/c ports and come back with some numbers. Oh yea, we'll need numbers at 1500 rpm too.

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Jim