How you know this is the problem
The signature is a system that stops cooling with no other symptoms: the breaker is fine, the outdoor unit is fine, and nothing sounds wrong. That is a float switch doing its job.
Other signs point the same direction:
- Standing water in or around the drain pan under the air handler.
- A water stain on the ceiling below an attic-mounted unit.
- A musty smell when the system kicks on.
- Water dripping from the secondary drain line outside — often above a window.
The float switch is a feature, not a fault
Most properly installed systems have a float switch in the drain pan or the drain line. When water rises, it opens the control circuit and shuts the system down.
Homeowners sometimes find this switch and bypass it to get cooling back. Do not. The switch is the only thing standing between a clogged pipe and water running through your ceiling drywall. The repair bill for the clog is a fraction of the repair bill for the ceiling.
Clearing it yourself
Find where the white PVC drain line exits the house outdoors — usually a stub of pipe near the condenser or beside a window. Turn the system off at the thermostat first.
Seal a wet/dry vacuum hose over the end of that pipe, using a rag or your hand to make the seal reasonably tight, and run it for two to three minutes. Most clogs come out as a slug of black sludge. Empty the vacuum outside, not down a sink.
Then find the access point near the air handler — a capped tee on the drain line — and pour roughly a cup of distilled white vinegar in. Vinegar kills the algae that caused the blockage. Replace the cap.
What not to pour down it
Skip bleach. It is harsh on the glued PVC joints and on the metal drain pan, and when it reaches your condensate the residue can corrode the coil it touches. Vinegar does the same job without the collateral damage.
Also skip the garden hose. Pushing municipal water pressure backwards into a drain line can force water into the air handler itself.
When it needs a technician
Call if the vacuum does not pull the clog free, if water is already in the ceiling, if the line reclogs within a few weeks, or if the system stays off after the line is clear and the pan is dry.
Frequent reclogs usually mean something structural: a drain line with no slope, a missing trap, or a line that was never flushed on a maintenance visit. A line that is pitched correctly and treated twice a year rarely becomes an emergency.
Want it measured instead of guessed?
The readings that settle this — pressures, superheat and subcooling, amp draw, static pressure — take a visit. You get the price in writing before anything is replaced.
(904) 467-1100