My walk in cooler won't hit the temperature set when it is hot outside. When the temperature was cold outside my cooler was fine but now its starting to get warmer outside the cooler stays between 42 to 50 degrees when I have it set at 32 degrees.

Have you had this unit serviced lately? It can be anything from clogged coils to low on coolant.

What is the ambient temp where the unit is sitting?

I work on a lot walk-in coolers and the number one problem is dirty coils and fans. Go to a supply house that sells heating and air conditioning parts and purchase a gallon on alkali coil cleaner and rubber gloves, apron, and a face shield. Turn off power to the walk-in cooler and drop the drain pan. You will want to clean it and flush out the drain line, too. Spray down the coils and the fan blades. The cleaner should be diluted 1 gallon of cleaner to two gallons water in a three gallon plastic pump sprayer. Put the water in first and then add the cleaner. Spray on in a stream in the coils and then adjust to a spray slightly for the fan blades. Let foam for about five minutes and then wash off with a water hose nozzle in the opposite direction from how air flows through the coils. After that clean the condenser coils. You will have to empty the cooler to clean the coils because you do not want coil cleaner on your food. This solution will clean off grease off anything. You can clean all of the coils in your business with this coil cleaner and save a lot of electricity.