How can I fix my rv refrigerator?

I have a 1987 Okanagan Class C 24' Motorhome. The motorhome was given to me and the refrigerator doesn't work. The fridge is a Dometic Model #RM 2600. Any ideas of why is doesn't work, and some tricks I could try on my own? Does anyone know how much it would cost to replace the refrigerator?