Cooling care falls into two groups. One group is routine and safe for a homeowner who turns the power off first. The other group involves refrigerant, electrical parts, or sealed components, and it belongs to a licensed technician. Sorting the two before the weather warms makes the season easier to plan.
What you can do
Turn off power at the disconnect box beside the outdoor unit, and at the thermostat, before you touch the cabinet. Replace the indoor filter on the schedule its label gives, and note the size printed on the filter frame so the replacement fits. Keep leaves, grass, and debris away from the outdoor unit, and keep the clearance the installation manual names. Rinse the outer coil gently with a garden hose, spraying from the inside out where the panels allow, and do not use a pressure washer. Check that the thermostat is set and responds. Keep a short log of the run, including any change in how long the system runs.
What belongs to a technician
Leave refrigerant alone. That includes checking charge, finding or repairing a leak, and any brazing on the lines. Leave electrical parts to a technician as well, including the capacitor, contactor, and fan motor. Any work inside a sealed component needs trained hands. If the indoor side has a gas furnace, the gas side belongs to a licensed technician too.
What to ask for in writing
When a technician visits, ask what they checked, what they found, and what they changed. Ask whether the old part is returned to you, and whether the work appears on the paperwork for the unit. Ask for each line of work to be listed separately so you can compare it later. If the system has a known age, check its install year against the typical service life on the central air conditioner page in this index. That comparison is a planning input, not a verdict on the unit.