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Discussion Starter #1 (Edited)
OK, here’s an interesting one…..

Air con was working last year, but condenser was leaking. Just fitted a new condenser today and the guy turned up to charge it (good guy, used him before)

Vacced the system down, it held a good vacuum, then went to add gas and found the compressor wasn’t cutting in. After lots of messing around we find that there is no power getting to the compressor. We powered it directly to gas and oil the system and everything works great, nice and cold and electric rad fan cutting in when it should (it was seized, I freed it off during the new condenser install)

So we started checking components. The first thing that was obvious was that turning on the air con or re-circ button resulted in a rise in the revs so the system saw it had gas, infact the system is all working perfectly, except no power is getting to the compressor.

Checked all the 4 fuses, all ok. Shorted out the 2 sensors on the dryer, one turned on the fan and the other caused the revs to rise or fall, confirming what we had seen earlier. Shorted out the sensor in the passengers foot well that shuts off if the system is too cool (it turned the air con off for a while to let it 'warm up') so that was working too.

Looked at the sword connection, all appeared ok. I had changed the pollen filter since the system had worked last, so the sword was a prime suspect, but it all seemed fine.

Infact EVERYTHING is fine, except the compressor isn’t being powered. Obviously there are several things inline on the compressor’s power feed that are interrupted to prevent the compressor running in case of problems. But as far as we could see we had eliminated them all. It feels like a sensor down, a blown fuse or a bad wiring connection.

We’ve run out of things to check, air con worked fine last year until the gas leaked out, but all components were fine. The system's now gassed and oiled with a brand new condenser, sat there doing sweet FA

The only other things that are slightly strange, but I don't think have a bearing, are the outside temp sensor was reading very low when I first re-connected it (30 degrees) bit since seems to have reset itself and is working fine, and I have low oil and pad wear warnings just come up as it's coming up for a Service 2. But I'm sure neither of them act as a cut-out to the compressor, do they? I've run the car 50 miles tonight with the air con turned on and it hasn't suddenly started working so that seems to rule out a bad connection...

Who’s got any ideas ??????
 

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Mike,
i have been suffering the same problem with air con on my E34 - it was wiring mess and it took me about 6 month to find required wiring diagramm and to let machaniccs to find it ;) The reason was the incorrect installation of some wire distribution unit under the hood (it happened before i own that car)
There are some different types of air con sysytems exist on M5 and you have first identify which one is installed on yours.
Good luck with getting the cool comfort back
Andrey ;)
 

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Discussion Starter #3
Thanks for the reply Andrey

Mine is a '95 car with a standard non-climate control system. It was working fine for the last 3 years but has now stopped. Nothing has really changed and no wiring messed around with. I have just been out playing with sensors again but nothing I do will engage the compressor.

Anyone else got any ideas? This is driving me mad.... grrrrrrr
 

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Mike,

There must be a relay somewhere to power that clutch. Never went looking for it so can't even guess where it might be.
 

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Discussion Starter #5
That's what I am starting to think. In the fuse box, the yellow relay at the back that has 5 legs.....if I remove it then the idle speed drops so it's obviously Air-con related, I'm wondering if it has semi-failed. All the other relays are different so I really need to swap it from another car to see if it is that. Just got back from 20 mile drive, outside temp hit over 100, typical...... grrrrrrr :mad: :mad: :mad:
 

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Discussion Starter #7

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Mike

The clicking noise you can hear is a little pump which scavenges moisture from a drain under the evaporator and dumps it out of the bottom of the car.

The compressor's only got two connections - one to the compressor control relay, and the other to ground.

The control relay (K19) is in the front power distribution box, which takes power from 15A fuse 9 and 7.5A fuse 29 (also both in the front PDB)

This is the one, enjoy my photos while they last, my LE finishes on eBay tonight and I won't just be able to nip out to take photos any more!!



Cheers,
Andy
 

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Discussion Starter #9
Thanks mate, perfect....

I'll go and see if it's powering up ok and switching
 

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Mike

It's probably not the fuses, because they power other things too, the auxiliary water pump at least (if I remember correctly)

If it's not that relay, at least you can test the continuity of the wiring from the relay to the compressor. Good luck.
 

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Discussion Starter #11
You're right, fuses have been checked and re-checked. It sounds like a control unit has gone down

Off to look now :)
 

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Discussion Starter #12 (Edited)
It's working fine Andy, half pulled it out and you can feel it clicking, switched it with another the same and that worked too. Do you think that is the CONTROL UNIT AIR COND.-BREAK DEVICE I mentioned? Do you think it goes direct from there to the compressor? In other words, is that the last switched point or are there sensors in between the black relay in the fusebox and the compressor?

If so I'll start tracing the power wire from fusebox to compressor, there must be a break....

edit: looked at the pic again, the CONTROL UNIT AIR COND.-BREAK DEVICE seems to be a different shape....

Maybe it isnt fitted to our model
 

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There's nothing inbetween the compressor and that relay except wire. Have you checked the continuity of that wire?

The switching aspect of that relay is controlled by the climate regulation module and switching unit - the sword thing by the cabin filter.

Not sure how much diagnosis you could do outside that, other than swap one over to try it.
 

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Discussion Starter #14
It's my next job, just letting the engine cool down :)

Do you happen to know which wire it is? Looks like number 5 judging by the little pic on the relay?
 

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Discussion Starter #17
Infact if I just short it and put power to the middle connection the compressor should cut in then....

will try
 

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Discussion Starter #19
Andy, you bloody hero :M5thumbs: :M5thumbs: :M5thumbs:

There was a break somewhere in the wire. Traced it as far as I could back from the compressor until it went into a main loom and the continuity was good. Spliced a wire into it and ran it across the back of the bulkhead and into the fuse box, splicing it into the correct wire...

Et voila !

Brilliant call, I owe you a beer mate
 

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Discussion Starter #20
I did discover one annoying thing, with the lower slider across to allow footwell ventilation, the passenger side blows nice cold air and the drivers side blows red hot air :mad:

Obviously a flap not shutting somewhere, looks like it's the top 2 sliders only in the summer then.... :3:
 
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