AC Outside Unit Not Running?

• The outdoor fan runs but you cannot feel or hear the compressor humming — the compressor is trying to start but the capacitor is too weak to get it spinning
• A brief two-to-five-second hum followed by silence, repeating every few minutes — the thermal overload in the motor is tripping on each failed start attempt
• The outdoor unit runs normally but the house stops cooling on the hottest afternoons — a compressor starting to lose efficiency under peak load before it fails completely
• Higher-than-usual electric bills despite no change in thermostat settings — a straining compressor drawing extra amps before it gives out
• The breaker for the outdoor unit trips once or twice and then holds — a marginal capacitor or contactor on its last legs before full failure

A capacitor that has been through eight Tampa summers has almost certainly degraded below its rated microfarad value. Capacitor life is inversely proportional to operating temperature, and outdoor units in Tampa sit in direct sun at 110-plus degrees for months at a stretch — conditions that cut rated capacitor life in half compared to a northern climate. If your system is eight years or older and the outdoor unit stops running, a capacitor failure is statistically the most likely cause. It is the single most predictable and preventable outdoor unit failure in this climate. During any annual tune-up, ask us to test capacitor microfarads and document the reading — you will see it decline year over year before it actually fails.

Capacitor and contactor failures in Tampa peak in June and July, when daily high temperatures first sustain above 93 degrees and outdoor units run under maximum load for the first time after the spring. A capacitor that tested at 90 percent of its rated microfarad value in April may drop below the functional threshold by the third week of June. Contactor failures spike in August and September after the full summer of thunderstorm-related power surges have pitted and burned the contact surfaces. Plan any outdoor unit maintenance before Memorial Day — by mid-June our call volume for outdoor-unit-not-running is at its annual peak.

• February or March: Rinse condenser coil fins with a garden hose from the inside out — spray through the top grille, not from outside in. This removes oak pollen before it gets packed solid by spring rains.
• April (before season): Have capacitor microfarads tested and documented. Capacitors reading below 90 percent of rated value are near failure and should be replaced before peak cooling season begins.
• Monthly May through September: Clear any vegetation that has grown within 18 inches of the cabinet sides. Lantana, ixora, and ornamental grasses common in Tampa landscaping can grow six to eight inches a month and choke airflow around the condenser.
• After every major thunderstorm: Inspect the disconnect box for moisture entry and listen for unusual sounds on first startup. Tampa’s 90-plus annual thunderstorm days mean surge-related damage is the most common non-maintenance cause of premature outdoor unit failure.