I recently learned to my surprise from Blueyonder's thread and Steamdrivenandy's explanation that the modern fridges fitted in new Eribas operate solely on 12v from the leisure battery.

On older vans, however, the three-way fridges that used to be fitted operate on gas or 240V mains (when on site with electical hook up) and also run on 12v from the car electrical system when towing.

Just before we set off on our recent UK trip on the hottest day of the year so far, I noticed that the red light in the switch on the fridge fascia panel was not illuminating when attached to the car with the ignition switched on. With our previous Astra the light only came on when the engine revs were raised above idle but with the Audi the light should come on immediately the ignition is switched on, even without the engine running. This means that if the car and caravan were left connected with ignition on and the engine not running, the car battery would eventually discharge.

Another thing I've learned from this forum is that even if the red light does come on, this doesn't necessarily mean that the fridge is working on 12v, only that there is power to the illuminated switch. Being a pessimist by nature, I always expect the worst so when my red light didn't come on I convinced myself that my problem was due to something horrendously complicated and therefore expensive to resolve.

While we were away, JohnE and I exchanged a number of texts in which he talked me through the checks to be made with my multimeter to identify the problem and, by a process of elimination, I found that the fridge relay in the BIP unit was at fault. I did a temporary repair by cutting off the plastic cover and cleaning the points with fine wet and dry paper. This worked (sort of) but replacement was clearly needed.

Fortunately, I have a mate who runs an electronics business from home servicing and repairing milking parlour control systems (talk about niche work) and when I asked where to obtain a relay, he said "How many do you want? I buy them by the hundred."

This is what the relay looks like:

Relay01.jpg - Bild entfernt (keine Rechte) Relay02.jpg - Bild entfernt (keine Rechte)

The one on the left is the original and the one on the right is the new replacement. On the original you can see where the relay has overheated, melting and discolouring the plastic at the switch end of the casing. You will also see that the new replacement is sealed whereas the original relay's cover could be unclipped and slid off.

Replacing the relay is simplicity itself, just pull the metal retaining clip off the relay, pull the old unit out (you may need fine-nosed pliers to be able to grasp it), push in the new one taking care to get it the right way up and refit the metal clip. Dead easy!

This is where the relay is located in older vans with a BIP unit:

Relay03.jpg - Bild entfernt (keine Rechte) Relay04.jpg - Bild entfernt (keine Rechte)

The relay socket is to the right of the switches; in the left hand picture you can see the metal retaining clip that has to be released and in the one on the right the new relay in place.

With the car electrics connected and the ignition switched on there is now an audible 'click' as the relay operates and the red indicator light now illuminates.

Fixed.

In future I shall carry a spare relay in my emergency kit of fuses, bulbs and crimp-on connectors.