Safe checks first
- Confirm you have one. A small box on the line-set run or above the indoor unit, sometimes audible as a brief whirr after cooling stops. Gravity-drain installs (most wall units with a downhill run) have no pump - go to leaking water instead.
- Constant running or clicking. A float switch stuck on debris runs the pump dry nonstop - the rattly buzz people report. Power the system off at the breaker; if the reservoir and float are accessible without opening wiring (many have a clip-off sump), lift out debris and algae, rinse, reseat.
- Water backing up / unit shutting down. Most pumps wire a safety float to cut cooling before an overflow - a mini split that stops cooling on humid days with a pump in the line often means the pump lost prime, clogged, or died, and the safety did its job.
- Check the discharge line. Kinks, a crushed section behind furniture, or an outlet frozen in winter block the pump's push. Follow the small vinyl line where visible.
- Noise normal vs not. A short purr after each cooling cycle is the design; continuous operation, gargling, or loud rattling is a flag.
Beyond the safe checks (technician scope)
Pump replacement (wired into the unit's power and the safety circuit), safety-float rewiring, and relocating a pump that was always marginal for its lift height. Pumps are consumable - a several-year-old unit that failed isn't a mystery, just maintenance.
When to stop and call
Water reaching drywall or flooring (stop cooling at the breaker first), any burning smell at the pump (it has a small mains motor - power off), or a second failure within a season (the installation needs rework, not another identical pump).