By late July, your AC has been running 16-plus hours a day for two months. Most failures we run in August started as small drifts in June or July that nobody noticed. Here are six mid summer AC checks any Florida homeowner can do in about 20 minutes with a $20 toolkit. None of these replace a professional tune-up, but all of them surface problems early - which is the difference between a scheduled service call and an emergency one.
What you need
- A new air filter in the correct size.
- A garden hose.
- A cheap infrared thermometer ($15-$25 at any hardware store).
- A piece of paper or a tissue.
- A flashlight.
1. Filter (60 seconds)
Pull the existing filter and hold it up to a light. If you cannot see light through it, the system has been choking for weeks. Replace with the same MERV rating you have been running (most homes are MERV-8 to MERV-11). Write the install date on the filter frame in marker. If the filter is visibly grimy at less than 30 days, that points to a duct leak pulling attic dust into the return - worth a tech visit.
2. Register airflow with a paper test (3 minutes)
Hold a piece of paper or a tissue under each supply register with the AC running. The paper should pull up firmly against the register. Walk the whole house. Look for:
- One or two registers with much weaker flow than the rest - usually a crushed or disconnected flex duct in the attic.
- All registers weak - a dirty filter, fouled coil, or failing blower.
- No flow at all from a register - duct fully disconnected or damper closed.
Note which rooms are weak. That information saves real diagnostic time when a tech does come out.
3. Outdoor unit clearance and rinse (5 minutes)
Walk to the condenser. The two-foot rule: nothing within two feet of any side. Clear:
- Shrubs and overgrowth that have crept in since spring.
- Lawn clippings, palm debris, mulch piled against the cabinet.
- Stored items. We see kayaks, hose reels, and trash cans within a foot of condensers all the time.
Then kill the disconnect, pull large debris by hand, and rinse the cabinet top-down with a garden hose on gentle pressure. Top-down only. No pressure washer. Restore power once the unit has dripped for 10 minutes.
4. Condensate flow (3 minutes)
Find where the condensate line exits the house - usually a small white PVC pipe outside near the air handler or the laundry. With the AC running on a hot afternoon, you should see a slow drip or a thin stream of water coming out. If it is bone dry on a 90 F day, the line is either clogged upstream or running to a different drain you have not located. Pour a cup of distilled white vinegar down the access tee at the air handler (the vertical capped stub on the drain line), wait 30 minutes, and recheck.
If you see standing water in the secondary drain pan under the air handler, stop and call. That means the primary drain is fully blocked and the safety pan is catching the overflow. We covered the full procedure in our condensate-clog post.
5. Supply-return temperature differential (5 minutes)
This is the most useful single check on the list. With the AC running in cooling for at least 15 minutes:
- Point the infrared thermometer at the air coming out of a supply register closest to the air handler. Note the temperature.
- Point it at the return grille (where air enters the system). Note that temperature.
- Subtract. The difference is your delta-T.
A healthy residential system on a hot day should show a delta-T of 16-22 F. Below 14 F suggests low refrigerant, a fouled coil, or weak airflow. Above 22 F can indicate restricted airflow or oversized equipment short-cycling. Either is a reason to schedule service. The infrared method is approximate - a tech with a probe in the duct gets a more accurate number - but it is more than good enough to flag a system drifting out of spec.
6. Thermostat behavior watch (5 minutes)
Stand at the thermostat with the system running and watch one full cycle. Specifically:
- How long does the cycle run? A healthy cycle in summer is typically 15-25 minutes. Cycles shorter than 7-8 minutes are short-cycling - a sign of a problem.
- How quickly does the room recover after the system cuts off? A quick rebound (more than 2 F in 5 minutes) means the room is running close to its cooling capacity.
- Does the indoor humidity sit above 60% during a long cycle? The system is failing to dehumidify. Often the first symptom of low refrigerant or a tired compressor.
- Does the thermostat actually call for cooling when temperature exceeds setpoint? Bad batteries (in non-powered stats) and dying displays are surprisingly common.
What the results say
- Filter clean, registers strong, condenser clear, condensate flowing, delta-T 16-22 F, normal cycles: system is healthy. Continue monthly filter changes.
- One or two minor flags (weak airflow at one register, slightly low delta-T): schedule a tune-up at your convenience.
- Standing water at the air handler, delta-T below 12 F, ice on refrigerant lines, frequent short cycles, humidity stuck above 65%: stop, call. These are signs of imminent failure or active damage.
When to call us
Mid-summer is when small drifts become emergency calls. We run tune-ups and diagnostics throughout July and August across Punta Gorda, Punta Gorda Isles, Port Charlotte, North Port, and Cape Coral. Diagnostic visit is $99. Call (941) 205-6331 or request service.