Thanks for including the picture. That's helpful.
I spent 15 years running the office of a small hvac repair and installation company in south Texas.
Call someone to come out and check your system. Ask nicely and they'll show you how they clean the coils and explain what else you can and should do and how often.
Keep in mind, it is July and there are a lot of people with a/c problems so don't expect them to spend too much extra time. Have them show up on a week with nice cool weather. All the techs I've met enjoy talking with people that show an interest in learning how to keep the units running at their best.
I clean the coil myself at the end of every cooling season and have an a/c tech come out and check the system every other year.
Never use a brush. Those metal fins are very fragile and once bent, are almost impossible to straighten like they were. They cover the evaporator coils. The coils contain the coolant. The entire "A" shaped unit is called a condenser. (not a radiator, that's in a car)
It is possible to damage the coils while cleaning the unit. They cannot be repaired but must be replaced. Depending on the size of the unit and type, this will cost between $1,000-$3,000. Again do NOT use a brush. It's rarely necessary. From your picture, I'd let a tech clean it, show you how, and you clean it at the end of every a/c season after.
Also, I bet either the air filter is the cheapest least effective one available, is completely clogged, or there isn't one.
Recommend a 3-month filter and CHANGE THE FILTER RELIGIOUSLY.
Yes, I am shouting. This is the single most important thing to do to keep the a/c running. Buy a year's worth. Mark it on the calendar. Change the filter regularly.
Let me rant a bit:
People were always happy to see our techs. For about a minute and a half. Then they'd start complaining about how long it took for them to get there, how miserably hot they are, how much life sucks without a/c, and just how long is this going to take. Mean-while the tech is eyeing the stuff in the hallway in the way of the pull down attic stairs wishing he was already in the oven of an attic so he could just get to work.
Apologies for this being so long.