Car is a 92 400E. AC normally works great but a couple of times in the last week it wouldn't work - just blows hot air. It seemed to start to work and would then cut out. There's a fault code 6 on the Base Module which is "Electromagnetic A/C Compressor Clutch Blocked". No codes at all on the AC socket. So what are the possible causes of a "blocked" compressor clutch?

Hi The base module will cut off the power to the a/c compressor if it does not get the right info and or signal from the a/c pressure switch,rpm sensor on the back of the compressor.You can have a problem getting code via a tester if the pressure switch is inop,try yo manualy pull codes from the push button control unit,also make sure you have no belt slippaged or a binding compressor and all connections are clean and tight,and freon level good.joeym

. . Menu#8; says "A/C clutch is frozen/jammed or V-belt broken".

When I got that DTC, it was my compressor was 'frozen'. Bet this compressor is on its way out??? Or maybe it's just slipping??? Will give the same DTC.

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Regards . . . . JimF
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'94 S500 Cpe

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There's been no apparent trauma - it will start to cool and then just switch to hot air. The fault code is #6 from socket 8 (Base Module) on the 38 pin connector - just says the AC compressor clutch is "blocked" - which is not as harsh, or as descriptive, as yours. I should have remembered that the compressor won't come on when the freon is low. In any case I'm going to be optimistic and start with joey's idea that the freon could be low - it hasn't been checked in a couple of years.

a code #7 that says "v-belt slipping". For my car #6 and #7 have been combined into one DTC.

All I can say, is that was the code that I got (#6) just before the compressor finally froze. It would come on for a few seconds or so, then go off. And it was almost fully charged! Hope yours doesn't come to that.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Jim, that's what it's doing - coming on for a few seconds then quiting. The freon was not low - I added a little but that clearly was not the problem. I can't see that the belt is slipping. But there's something telling the clutch to disengage.

Try cleaning out the compressor clutch. Any accumulated oil/grease/grime can cause it to slip and trigger the cutout circuit. A spray can of brake cleaner into the clutch gap is a good start. It's cheap, it's easy, and it's been known to fix cut-out problems.

If you have a set of feeler guages, check the clutch gap. Ideal is 0.50mm. Clutch engagement becomes unreliable when it gets in the range of 0.80 - 0.90mm. It's possible to adjust it be pulling the front clutch plate and removing/swapping different spacers (essentially small, thin washers). A decent a/c shop will have kits of spacers for Nippondenso compressors.

- JimY

JimY - thanks, I will try both ideas.