Having a residential roof top air conditioner can be convenient, but there are also some drawbacks. The main one is that it can be easy to overlook maintenance on the main unit when you don't see it nearly every day. Fortunately, knowing things you need to look for and combining it with a regular inspection schedule can help you avoid issues.
Issue #1: Blocked drains
Condensation collects in a rooftop unit just as it does in ground-based AC units. This is why most rooftop units are connected to drains. If you walk around your home you will likely find the drain, as it will be a small water spout sticking out from the wall. Some are placed high up, while others run down the wall and emerge near the bottom. If this drain becomes blocked by dirt or algae growth, water cann't flow through it. It instead collects on the roof where it can damage your roofing or cause a leak. There should be apparent moisture periodically throughout the day when the AC is running. If not, then you need to check the drain pan under the AC and the drain itself for leaks. Usually you can flush these out with a mild bleach solution and solve the issue.
Issue #2: Dirty condensing units
The exterior portion of the condensing unit is made up of small plastic fins, which is what gives the vented appearance to the outside of an AC unit. Dirt and dust on these fins prevent the AC from cooling efficiently, so you need to hose off the outside AC unit once monthly during the cooling season. Rooftop units are usually more exposed, which means they are more likely to get dirty. Sometimes, flying debris from windstorms bends the fins, which also compromises cooling. Once a year before the cooling season begins, use a fin comb tool to straighten out the fins so that they continue to provide efficient cooling to your home.
Issue #3: Nesting birds
Your AC unit provides a sheltered spot on your roof, which can attract birds looking for a nice place to nest. This is especially true at the start of the nesting season in spring with the AC unit may not be turned on and making noise yet. Nesting materials block airflow around the AC, and they may also get into the unit and compromise it. Check for nesting birds in the spring before turning on the AC for the first time, and remove any debris they may have left. You can also put up scare devices or anti-bird devises, such as bird netting and spikes, to avoid the problem completely.
For more help with your rooftop AC, contact an HVAC repair service in your area.