Strange noises from area of fridge when accelerator pressed

[Pat]

Folks - this is driving me nuts. I have a 98 Cali with the usual lovely fridge, which has a mighty, long battery underneath it as well as the charger/mains power supply.
It works brilliantly, even if now and then it makes a bit of noise on startup after a long dormant period.
But - recently I notice that when I press the accelerator while moving, or stationary with engine running, I hear a sort of crackling noise from the region of the fridge. I'm on lockdown, strictly speaking "cocooning", so I have nobody to sit in the back to track it down. It reminds me of electrical arcing noises. It doesn't seem to matter if the fridge is running or not. Or perhaps two pieces of expanded polystyrene rubbing off each other! Rev up, the noise increases, slacken off and it dies.
I removed the panel, disconnected the positive lead off the battery, removed a couple of the connectors going into the power unit - no difference. An overvoltage protection circuit, perhaps?
I can't think that there's anything else back there that could be involved. It's my daily driver so I can't take everything out and leave it disassembled for days while I figure it out.
Any ideas? Thanks. P@

 

[sidepod]

Wow. That’s a new one. Just check all of the electrical stuff is secure etc.
I did have a similar thing last year. Turned out to be the fridge/cooker unit rubbing slightly on the bodywork. Drove me fookin Cream Crackers!

 

[westfalia]

Wow. That’s a new one. Just check all of the electrical stuff is secure etc.
I did have a similar thing last year. Turned out to be the fridge/cooker unit rubbing slightly on the bodywork. Drove me fookin Cream Crackers!

View attachment 59698

First impressions...
Thumb nail needs cutting, just looked at mine... hey ho waddya know. So does mine.

 

[Pat]

Wow. That’s a new one. Just check all of the electrical stuff is secure etc.
I did have a similar thing last year. Turned out to be the fridge/cooker unit rubbing slightly on the bodywork. Drove me fookin Cream Crackers!

Thanks - I'll go have a poke at the hinges and anywhere that could be rubbing, maybe spray in a bit of silicone here and there. It SOUNDS like arcing, but the time it happens is when there is a bit of vibration going on so 2 surfaces rubbing together seems more logical.
Should have learnt my lesson somewhat when the rubber on the sliding door gave sounds that were misleadingly un-rubberlike - GummiPfledge helped a lot with that.

 

[Rascal1]

I would have a look at the split charge relay.Perhaps it is arcing when you rev the engine and there is a bit more current going into the leisure battery. You could disconnect the small control wire and then the relay will not change over.Bit of a long shot but......

 

[WelshGas]

Thanks - I'll go have a poke at the hinges and anywhere that could be rubbing, maybe spray in a bit of silicone here and there. It SOUNDS like arcing, but the time it happens is when there is a bit of vibration going on so 2 surfaces rubbing together seems more logical.
Should have learnt my lesson somewhat when the rubber on the sliding door gave sounds that were misleadingly un-rubberlike - GummiPfledge helped a lot with that.

Sorted yet?

 

[Pat]

I would have a look at the split charge relay.Perhaps it is arcing when you rev the engine and there is a bit more current going into the leisure battery. You could disconnect the small control wire and then the relay will not change over.Bit of a long shot but......

OK Rascal1 I'll go look at that - you say a long shot but it jives with my suspicions. I really have this audio "image" in my mind of electrical arcing, and it corresponds to pushing on the accelerator, if I lift my foot it goes almost entirely away. Also I note the fridge battery doesn't seem to be charging fully and the reported voltage (on the overhead display) swings about from 14v+ to 12.5ish and back again in the space of a minute or two. Again my instincts are that it is occurring in a small maybe 1inch cubed black box with perhaps 3 wires going to it that is mounted on the side wall, away from everything else, charger, battery, fridge compressor. I am expecting to find this to be a split relay, or a Voltage Sensitive Relay. I guess it will be obvious if there is charring or pitting on internal metal bits?

 

[Pat]

Sorted yet?

No. Even though I am retired, and cocooned in my house, I haven't got round to opening up the panels again to sort it. Need to have the van ready to drive as I'm out in the sticks and the only transport I have. Will be moving "stuff" tomorrow for my big sister (LOL!) who is really confined to her house, now that the rules have been relaxed so we can go 20 km or anywhere within our own county. Don't know if the motor factors are open - maybe they are operating an order and collect service - probably just as easy to get the part from Amazon or eBay anyway.

 

[Pat]

Well, just a progress report with no progress! I removed what was making the noise - the split charge relay. The relay connects the leisure battery and the starter battery after the alternator signal wire goes to 12V-ish. I disconnected the heavy duty battery wires - the noise continued. Disconnected the "signal" wires and ground (in a plug) and the noise stopped. Reconnected the signal wire, put some paper between the relay contacts and the noise stopped. The relay looks spotlessly clean and as shiny as the day it was made. There is a spot of brown (resin??) on one of the posts carrying the switching signal that might be worth resoldering, though if it were broken the contacts would never "make" in the first place. It does get hot though as it has a resistance of 45 ohm and uses about 3 W all the time the engine is running.
So my conclusion is that the noise is chattering where the contacts are closed whenever the alternator is generating current but somehow are opening momentarily a hundred or more times a second. And the only explanation for that is that the control voltage is dropping from 12V+ to what, 6V? a hundred times a second when the pedal is pressed and THAT implies a diode or two is dead. I measured the AC on this DC signal and it is low 50 to 100mv when there is no acceleration, but goes up into volts when the accelerator is pressed and the chattering starts. So I asked a mechanic to look at the alternator, assuming he'd have a scope. Silly me, he doesn't. He said the alternator is fine, gives the correct charging voltage etc and looked a bit glazed when I asked about AC.
I'm not going to just buy a new relay just to try - the existing one looks fine and they are expensive. Ditto the alternator, which is a refurbished unit maybe 2 years "old". I used to be in the electronics business but don't have access to scopes etc and more.
Sorry to witter on - it's doing my head in. And I want to go wandering down to West Cork, and a working fridge is a big part of that.

 

[sidepod]

Blimey. Impressive. Have you tried running a separate wire from the Alt to the relay to see if that cures it?

 

[Pat]

Blimey. Impressive. Have you tried running a separate wire from the Alt to the relay to see if that cures it?

Not yet! It's one thing I'm going to explore, though, that there might be a dodgy connection or even a micro-break on this wire. But I had a thought in the scratcher last night - when electricals are doing something completely illogical, "rear indicators coming on when the brake is pressed" sort of thing, what is the first place to look, the 90% most likely culprit, the utter bastard that causes this hair-pulling experience?

Earth connections.

As a boat-trailer user, salt-water immersion a speciality, I should have remembered this. As soon as it stops raining I'm going to spend a little while tracking down where the negative wire from this relay goes and give it a good wiggle and check it for corrosion.

 

[Pat]

Just to report a little progress on this issue. The problem has gone away but I haven't solved it!

I got a bit disorganised and somehow lost the relay I had removed from the van. After 2 days of turning the house upside down, looking everywhere it could possibly be and all the places it could not possibly be, I realised I must have thrown it out with some junk VW bits - and the binmen had been.
So I had to buy a relay, didn't I?
Of course this one was "special" - 80Amp, screw terminals, hard to find 0 332 002 150. VW main dealer cost was something like €80. Same part from the net €40. But then I found Bosch had made an improved part- p/n. 0 332 002 168 and available from Amazon for less than €20. It's form/fit/function compatible with the older part - see attached photos. The only difference is there's an internal resistor across the coil.

If this hadn't turned up I'd probably have made do with a common 40A relay, though I'd have to change the switching terminals to individual spades, and the high current ones from screw terminals to large spades. These really are common - local motor factor had it, as did my local farmer's co-op. And marine outlets will have something like it for battery charging on boats.

And then I was getting my sailing dinghy (Drascombe Dabber) ready - and in it I found....the old VW relay. Yeah I don't know how either.

So I popped in the new relay, with just the switching signal and earth connected, and... it chattered away like the old one. I was heading off for 5 days in West Cork so I really needed the fridge, so I put back the old one, battery connection as well, and I put up with the chattering on my journey. Either it got less and less, or I got used to it. But it did charge the fridge battery, no problem at all.
Following week I got the "clock spring" replaced in my steering wheel so the airbag light would finally stay off, and the horn wouldn't occasionally beep on turns - and since then the relay chattering has stopped! Now this HAS to be coincidence, doesn't it?

So the problem is gone away, but I don't know why and it could come back any time. Still suspect the alternator D+ signal wire diodes.

at's one hefty relay!
Photo of the old and new diodes, and one showing the internals - that's one hefty relay!

 

[sidepod]

That is bizarre!! Presumably the battery was disconnected during steering wheel/air bag removal so could it just have been that?

Anyway it’s sorted

 

[Pat]

Yeah - there's no logic to it being connected to the replacement of the "clock spring". AFAIK the only connectors in there are the trigger for the airbag, and the voltage out to the horn. As you say the mechanic would have definitely disconnected the main battery when working on the airbag, so I guess it might have to do with poor connections, though I'm pretty sure there is a major earthing point near the leisure battery on the rear wheel arch metal. Think I'll do a session of inspecting ground connections, and terminals on both batteries, and the awkward to get at fuses behind the driver's seat, and clean them and wherever else is recommended (Vaseline?). Can't hurt.
Right - new starter goes in tomorrow (hope I bought the right one), new tyres on the front as well, airbag light has stayed off, and I just replaced the fiddly 5W wedge bulb in the number plate. Then a particularly good car wash and off to the lads at the CVRT (our equivalent to the DOE/Commercial MOT) for the annual test.