This is a followup to my previous answer. It turns out that changing the relay only fixed the problem for a few months. The underyling problem was that the voltage on the low voltage side was getting lower and lower (should have been 24V, got down to 12V) due to a faulty capacitor. (Changing the relay helped temporarily because the new relay needed less power to energise it.)
I later replaced C1, C2 and C3 which cured this voltage regulation problem. However be very careful if you do this. C1 is a high-voltage type and the whole circuit is a not a very brilliant way of generating 24V from the mains (no isolation; possibly wouldn't be allowed today).
Also the fridge went wrong in a different way a few months after this, and I gave up on it and got a new one!
Alex
June 2008