A little water dripping from your outdoor AC unit or off a rooftop package unit is usually just condensate doing its job. It's only a problem if the drip is heavy, constant, coming from an unexpected spot, or pooling somewhere it's causing damage.
This guide covers dripping around the outdoor unit and off rooftop units onto the roof. If water is showing up inside your house, like a ceiling stain or a puddle near a closet air handler, that's a different and more urgent situation. See AC leaking water inside instead. Not sure which symptom matches your unit? Start at the AC troubleshooting hub.
Why AC units drip water at all
Your AC pulls humidity out of indoor air as it cools it, and that moisture has to go somewhere. On a split system, the condensate drain line usually runs from the indoor coil out to a spot near the outdoor unit, and a slow drip there during a hot, humid afternoon is completely normal. On a rooftop package unit, everything (coil, drain pan, drain line) lives in one cabinet on the roof, and the condensate typically drains straight onto the roof or through a short pipe near the unit.
Arizona is dry most of the year, but during monsoon season (July through September) humidity spikes and so does condensate output. A unit that seemed bone-dry in May can drip steadily during a muggy August afternoon, and that's expected, not a malfunction.
Normal vs. not normal
Normal:
- A slow, steady drip near the outdoor unit or drain line opening on a humid day.
- Water pooling briefly under a rooftop unit's drain point after it's been running hard.
- More dripping during monsoon season than in dry spring months.
Worth checking:
- Water gushing rather than dripping, especially from somewhere other than the drain line.
- Dripping that continues heavily even on dry, low-humidity days.
- Water pooling on the roof deck instead of draining off the edge or into a designated drain, which can lead to roof damage over time on a rooftop unit.
- Ice or frost on the outdoor unit's refrigerant lines along with dripping — that points to airflow or refrigerant problems, not normal condensate.
Condensate line basics
The condensate line is a PVC pipe, usually 3/4 inch, that carries water away from the indoor coil. Dust and algae buildup can partially clog it over months, especially with the amount of dust Arizona pushes through return air. A partial clog doesn't always stop drainage completely. It can just make the drip pattern change, or push more water out through a secondary drain or overflow point than usual.
If you can access the line where it exits near your outdoor unit, a slow trickle even in dry weather usually just means the system is running and pulling some humidity. A sudden increase in flow from that same spot after months of nothing is worth a look, since it can mean a developing clog is forcing water out somewhere it doesn't usually go.
Rooftop units and roof damage
A lot of Valley homes run rooftop package units, and their condensate typically drains right onto the roof or through a short standpipe. Over years, that steady drip in the same spot can wear at roofing material, especially on flat or low-slope sections. If you notice a mineral stain or a soft spot developing on the roof directly below the unit's drain point, it's worth mentioning to a roofer or your HVAC contractor at the next tune-up, since redirecting the drain line a few feet is a simple fix.
When to call someone
Call a licensed HVAC contractor if the drip turns into a steady stream, if you see ice on the lines along with the drip, or if a rooftop unit's water is pooling instead of draining off. A technician can flush the drain line and check the drain pan and float switch in under an hour for most systems.
Look up any contractor's license at azroc.gov before scheduling. We list rated ac repair contractors in Gilbert and Casa Grande if you need someone local. If the drip has turned into a full system shutdown, our guide on AC not turning on covers the condensate overflow switch that can trip when a drain clogs completely.
Common questions
Is it normal for an AC unit to drip water outside?
Yes. A slow drip near the outdoor unit or drain line, especially during humid monsoon months, is normal condensate drainage. It becomes a concern only if the flow turns heavy, comes from an unexpected spot, or continues on dry days when humidity is low.
Why is my rooftop AC unit dripping onto the roof?
Rooftop package units typically drain condensate straight onto the roof deck or through a short standpipe near the unit. That's the designed drainage path. It's only a problem if water pools instead of running off, or if the same spot on the roof shows wear over time.
Can a dripping AC unit mean it's low on refrigerant?
Not directly. Dripping is a condensate issue, not a refrigerant one. But ice on the refrigerant lines combined with heavy dripping once that ice melts can point to low refrigerant or restricted airflow. If you see ice along with the drip, that's worth a technician visit.
How often should the AC condensate line be cleaned in Arizona?
Most contractors recommend flushing the condensate line during a seasonal tune-up, roughly once or twice a year given the dust load Arizona homes deal with. A vinegar or bleach flush every few months can help prevent algae buildup between professional visits.