Having a problem with low voltage after AC compressor was replaced.

In February, major maintenance, new tensioner, new timing chain, new guide rails, new belt, new super charger, new radiator hoses, water pump, the list goes on for non-engine parts like suspension, bushings, brakes, etc.. Oh, my crank pulley was replaced with an ATI about 2 years ago.

Recently installed a new AC compressor and now have a low voltage issue when AC is on. The AC has not worked for a year, but just got around to repair. Thought it may have been the AC clutch, but turns out the compressor had a leak at the front seal.

The low voltage issue was noticed after the AC compressor install, but I admit I would randomly (but not often) get the trifecta of dummy lights when at idle. The car still ran fine, but the check engine would stay on for a few start cycles and then go away. Never saw any problems with gauges, lights, etc..

The tech noticed the voltage at idle is at or falls slightly below 12v. When you rev engine the volts go up to 12.5. Tried replacing alternator, put in a new battery, disconnected power steering, checked both fuse boxes, checked and cleaned both ground straps...

Any other ideas or recommendations we can try? Any help or guidance is greatly appreciated.

 

Pretty sure that the voltage regulator is attached to the back of the alternator. Have you checked it?

 

I would assume he has checked this. Assuming its a new alternator, would this not be eliminated as a problem. I will speak to the tech tomorrow and double check, but he has been very thorough. I don't care what it is, I just want it fixed so I can get back on the road.

 

I will add this bit of info that raises questions...

The tech mentioned the BSD wire (white wire to alternator) at idle shows .05 volts, but when you give it gas (rpms), the volts drop to 0. Any thoughts on this?

 

Your symptom points to a problem with the alternator and/or the external circuit associates with it for it to generate DC electricity. As pointed out the regulator on this alternator should be mounted behind the alternator. I am not familiar with the alternator in the Mini. However I know very often when a good alternator fail to produce power it can be due to the field coil is not energized. I think modern alternators are designed to free spin (not producing power) during engine cranking. This is likely managed by the DME (ECU) in the Mini.

In page 128 here the white wire goes to the DME. There are also blk/yel goes to the instrument cluster. More significantly is F38 10A fuse. I suggest checking F38 fuse.

On the VW Vanagon, the alternator field coil circuit is completed by the instrument cluster indicator. If you forget to connect the instrument cluster, the alternator will produce no charge. However, I don't think the Mini's work this way. I think with the Mini, the white wire that goes to the ECU signals to the regulator to energize the field coil.

 

Thanks for the detailed response! The tech has gone through everything you mentioned. We are going to try another new alternator that comes with a brand new regulator. If this does not resolve the issue, he believes it will come down to a bad DME, but I'm not even sure that is the issue. Which means a trip to MINI service and a very hefty bill.

 

Madmike007,
Was that voltage drop with A/C on normal for these cars? I am monitoring mine now and it does the same thing. I am thinking it maybe normal since I never had a voltmeter attached and do now since I replaced my alternator today and want to track it's behavior.
Thanks
Tom