Who is the fridge mfgr. , model and age? That may trigger someone elses memory who had a similar problem.
Did it ever work well?
Have you checked that the fridge is getting proper voltage while running? Important.
Do you have good venting for the heat that the fridge pulls out of the food and itself and then has to expel to the atmosphere.
A lot of fridge "problems" are caused by poor venting.
Is there a vent at the top of the cavity the fridge resides in so the heated air can escape?
Is there a fan forcing the heated air out by that upper vent?
Is there a vent allowing air to enter the cavity at the bottom to supply that air and allow circulation.
As summer temps. climb especially if the sun beats on the side the fridge is mounted on all of the above become even more critical.