Fridge Repair Job - Strand, WC, 7139

We have got an Aim fridge that has been standing for 3 years.A friend of ours wants to buy it but when we switched it on the motor worked but the fridge did not get cold. There was no noise or anything. We would just like to know how much it will cost to repair it. We don't want to spend more on repairs than what we are getting for it. Thank you.