The room I have selected is where I stockpile my room. I've got a cooler there that's target temperature is set to -4c, but it wavers around 9c-10c, which spoils my food. I've had that heater a couple rooms over off for a couple of days, would that affect anything?
So it's hard to tell definitively from the screen shot, but here are some suggestions:
The number one loss of cooling in Rimworld is through doors. Everytime the door opens, your colonists let the cold air out. Consider installing an "airlock," a one tile hallway between your fridge and the rest of the base with two doors. Theoretically, both doors will never be open at the same time. Fridge doors are also excellent candidates for autodoors, as less time open means less airflow. You could also redesign so the fridge only has one entrance.
Different materials have different levels of insulation. Consider replacing your wood walls with stone or steel, and especially consider using double walls, which will keep the cold in and the heat out.
Different materials have different levels of insulation This has repeatedly been proven to not be true on the Rimworld subreddit. Most people assume it makes a difference, but it does not. I've personally tested it too because I used to rush stonecutting for a freezer. Double walls and airlocks, however, are the optimal freezer room solution.
Since you didn't post the entire screen, it's hard to tell, but it's possible that your outside temperature is too high for a single cooler to be able to make the room reach the target temperature.
Try Dallium's answer but if that doesn't solve your problem simply add another cooler to the room. Also keep in mind that generators also produce heat and it's a bad idea to have them right next to a place you're trying to keep cool.
