Thetford N3175 AES Fridge/Freezer Not Operating on 12V - Chausson 718 EB 2015.

[Windy66]

Hi All

The fridge has never worked on 12V (engine is running). Always Error 6 - DC Voltage Out of Range. It's not been a problem really until we recently started doing long driving runs to Spain (for e.g.) where the fridge contents get too warm. Yes the fridge works fine on gas (and EHU) so I could use gas when driving but, as you know, this is not recommended.

So I started looking into this. I found there was a 'Bridge' missing in the CBE box from FA2 to FA3. I found this looking at the CBE schematics and Chausson/fridge info on the web, plus reading others helpful advice. I decided to try applying the Bridge (with an in-line 5A fuse for piece of mind). Then start the engine and manually switching to 12V on the control panel, the error code changed to 'Error 7 - No “engine run” signal is present and control is in Manual DC mode.'

The bridge did it's job then.

I believe the Bridge should have been applied at build but never was. If anyone has some words of wisdom on this presumption and the 'Bridge' in general, I'd be more than pleased to hear your view.

So onto the next issue of no D+ (Error 7). My problem is where this may originate from? I need this info so I can diagnose the D+ is operating properly and will in fact protect the battery from discharge should the fridge be inadvertently left on. The fridge is supposed to be able to apply this protection. In fact, it is doing by reporting Error 7, now I've applied the 'Bridge'.

Note: I have removed the Bridge and only apply it when trying to diagnose what is happening.

I note from the CBE schematic that FA4 is "D+ Out". A likely candidate. But I can't seem to trace this through to the fridge. Somewhere, somehow a D+ is routed to the PCB connector of the fridge behind the fridge grill. If anyone, knows where the wire may go, I'd really appreciate your help.

Info an pics attached.

 

[Lenny HB]

The bridge is there to allow the fridge to run from the leisure battery when the engine is not running.

As yours is not working with the engine running I'd could be a problem with the D+ not switching the relay that supplies power to the fridge or the relay itself.

 

[Windy66]

Hi Lenny

I know you are an authority on this subject and thus take your advice accordingly.

So, from what you are saying, I should not use the Bridge and instead find out why the D+ is not switching the relay to apply power?

I wonder why then, the schematic (attached) shows a distinct connection to an "AES" fridge via (what I assume) is a Bridge connection. And of course the fridge (when connected with the Bridge) will not run unless the D+ is present?

Also that the fridge is reporting a D+ issue though now, when the Bridge is applied. As though it's supposed to work this way. However, if I look at the attached schematic, it reinforces what you are saying. The Bridge bypasses the relay. Which I assume is the one in the CBE between FA2 & FA3?

According to the diagram and the fridge error codes, the Bridge, seems to hand off the responsibility to the AES (Automatic Energy Selection) when it has the system logic to detect D+ is present or not. Why have the capability to fit a Bridge otherwise? Why do the diagrams / schematics state that the Bridge is for AES fridges? Meaning the Bridge is applied when an AES fridge is installed, yet removed when a manual fridge is installed?

Confused.com!

 

[Fat Albert]

There is another possibility that the 20A (Old PCB) or 25A (New PCB) has blown (Open circuit). This was mine half way through a trip around Norway. Good news was that even though the fridge was out of warranty, Thetford provided a new PCB to my dealer to fit. To make my life easier, if the 25A fuse goes again I have a fuse holder with the 25A fuse external from the PCB.

 

[Windy66]

Wow - I've seen this posted elsewhere before - the fuse board looks really dangerous. Mine is ok but a good shout on the idea of an external fuse setup

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[GeoffnDee]

Is there a separate module fitted marked - Boite Relais Securite- or - Separatore Elettronico SB100- if so, it could be worth checking . It may be under the passenger seat.

 

[Lenny HB]

There is another possibility that the 20A (Old PCB) or 25A (New PCB) has blown (Open circuit). This was mine half way through a trip around Norway. Good news was that even though the fridge was out of warranty, Thetford provided a new PCB to my dealer to fit. To make my life easier, if the 25A fuse goes again I have a fuse holder with the 25A fuse external from the PCB.View attachment 1083249View attachment 1083250View attachment 1083251View attachment 1083252View attachment 1083253View attachment 1083254

Blade fuses are terible for high current, if the contacts arn't very good they arc and you get that problem.

 

[Lenny HB]

So, from what you are saying, I should not use the Bridge and instead find out why the D+ is not switching the relay to apply power?

Yes I think you need to get a meter on it to find out why you are not getting a D+ signal to the fridge. CBE electrics are a nightmare my new van has them I'm still trying to get my head round as info is very poor.

 

[Fat Albert]

Blade fuses are terible for high current, if the contacts arn't very good they arc and you get that problem.

Unfortunately for me after a bit of research the only midi fuse I could find was a 30A. Not getting that warm fuzzy feeling about the extra 5 amps I moved the fuse externally and soldered the cable spades onto the PCB

 

[Windy66]

Is there a separate module fitted marked - Boite Relais Securite- or - Separatore Elettronico SB100- if so, it could be worth checking . It may be under the passenger seat.

Hiya - there are two behind the drivers seat and both been checked.

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[Windy66]

Yes I think you need to get a meter on it to find out why you are not getting a D+ signal to the fridge. CBE electrics are a nightmare my new van has them I'm still trying to get my head round as info is very poor.

Hi Lenny - I have my multimeter at hand and been using it extensively. I am qualified in electrical control systems and electronics - but sadly not auto electrics! But therein lies the problem, where to find the connector points from the D+ Out in the CBE to the fridge.

 

[Fat Albert]

At the fridge connections at bottom vent the orange cable is the D+ cable. Check there is voltage when the engine is turning and burning. Oops sorry about that got my aircraft head on.

 

[Lenny HB]

I just had a look at the Thetford fridge install manual that was pretty useless but it did look like the relay that switches the 12v supply to the 12v element when the engine is running is inside the Power control module (guess work as I've never had a Thetford fridge).
If that is the case the fridge just needs the D+ to work when the engine is running. As Fat Albert says check that the fridge is getting a 12v signal on the D+ input when the engine is running, if it is it could be a module problem.

 

[Windy66]

I just had a look at the Thetford fridge install manual that was pretty useless but it did look like the relay that switches the 12v supply to the 12v element when the engine is running is inside the Power control module (guess work as I've never had a Thetford fridge).
If that is the case the fridge just needs the D+ to work when the engine is running. As Fat Albert says check that the fridge is getting a 12v signal on the D+ input when the engine is running, if it is it could be a module problem.

Hi Lenny

Thx for looking at the manual. There is no D+ signal. Thats why I'm asking for cable routing information so I can trace it. Once I apply a D+, the fridge works as it should.

As mentioned previously, the Bridge needs to be in place for AES fridges. Manual fridges need it removing so the onboard relay can control 12V power utilisation. Hence the need for the D+ to work in my case

Thx

 

[Lenny HB]

As mentioned previously, the Bridge needs to be in place for AES fridges.

Should only need the bridge for running from the leisure battery but a lot of manufacturers don't do the wiring for this function.

My van has a DS300 I will have a look later & see if I can give you any pointers.

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[Fat Albert]

I have a Chausson 610 same fridge and DS300 distribution box. My bridge cable is in a plastic bag not used, the fridge on 12v comes from the Alternator via the starter battery and Hab battery because the D+ ties the 2 systems together. With the engine running, do you get the same voltage at the battery terminals? If no, then D+ problem or yes, then D+ must be working.

 

[Windy66]

Hi Fat Albert and Lenny.

Update. I found a bunch of relays and fuses at the foot of the drivers side door pillar.

I noticed a power connection was not pushed in properly (see attached). Although I don't know if this has much to do with the fridge and I can't say if the connection was sound before I reconnected it. I also pulled and checked all fuses I could find and pushed in all the relays properly. Some did indeed need to be pushed in to seat properly. I gave the whole setup down there a good visual inspection and reseated everything I could.

I had already removed the fridge pcb cover and pulled the High and Low DC, and also the D+ connector so I could get the multimeter on it properly.

I powered up main the panel and started the van engine. Low and behold, a D+ signal was now present! Switched off the van engine and the D+ disappeared.

So I powered up the fridge and it ran quite happily on the 12V when the van engine was running (D+ present). When the fridge was set to 'Auto' and the van engine was switched off, it reverted to gas. And visa-versa.

If I set the fridge to manual and 12V, when the van engine is not running, the error code on the fridge is Error 6. For completeness, I reconnected the Bridge and under the same scenario the fridge error code changed to error 7. I have removed the Bridge again because (as per Lenny's advice and reading the schematics), the fitting of the Bridge will enable the fridge to draw power from the Leisure battery. I don't want or need that in my scenario. I want instead for it to use the main vehicle battery and only operate when under van engine power (alternator). This I now have.

In conclusion, and in my case, the AES fridge works as it should (operates on 12V only when the engine is running) with the Bridge connected or not. Just different error codes are present.

Fundamentally, with the Bridge connected, it allows the responsibility of the 12V operation to be handed off to the fridge itself (needs a D+ to operate) because the Bridge enables power from the B2 battery (in my case this is the leisure battery) as a permanent high current connection to the fridge PCB. This permanent connection isn't a problem with an AES fridge as it will not draw current unless a D+ connection is present (engine is running) at the fridge. A manual fridge will however draw current unless the fridge is switched off at the panel.

With the Bridge disconnected, the responsibility is with the van habitation logic instead (via the relay). The relay (triggered by the presence of a D+ signal) comes into play and allows power from the B1 battery (vehicle) AND the B2 battery (Leisure battery in my case).

So thank you for your support and help. I really appreciate your input.

 

[Windy66]

I have a Chausson 610 same fridge and DS300 distribution box. My bridge cable is in a plastic bag not used, the fridge on 12v comes from the Alternator via the starter battery and Hab battery because the D+ ties the 2 systems together. With the engine running, do you get the same voltage at the battery terminals? If no, then D+ problem or yes, then D+ must be working.

See update but yes, I agree the D+ relay means both B1 and B2 batteries are in use.

 

[Fat Albert]

I'm glad you got to the source of the problem. When my fridge failed, we were well above the tree line in Norway and it was definitely not flip flop weather. If you look at image 3780, I'm sure that orange wire is D+ but I never chased the wires to confirm, maybe others could confirm or deny.

 

[Windy66]

I'm glad you got to the source of the problem. When my fridge failed, we were well above the tree line in Norway and it was definitely not flip flop weather. If you look at image 3780, I'm sure that orange wire is D+ but I never chased the wires to confirm, maybe others could confirm or deny.

Yes defs the orange wire. See also attached schematic.

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[Windy66]

I have removed the Bridge again because (as per Lenny's advice and reading the schematics), the fitting of the Bridge will enable the fridge to draw power from the Leisure battery. I don't want or need that in my scenario. I want instead for it to use the main vehicle battery and only operate when under van engine power (alternator).

Correction to the above remark:

I have removed the Bridge again ....., the fitting of the Bridge will enable power to the fridge via the leisure battery, irrespective of any fridge settings or if the van engine is running. I don't want or need that in my scenario. I want instead for the van main battery B1 to be used and be connected only when the van engine is running. Yes, the leisure battery B2 will also be connected (as well as B1) when D+ is present (van engine is running) but that is fine. Power will still be isolated from the fridge and thus the wiring leading to it, via the D+ relay.