My float switch tripped. How do I reset it and clear the drain?


     If the air handler’s float switch has tripped, the primary condensate drain has stopped up due to a blockage, and the blocked water has tripped the float on the float switch.  Most of the time an algae growth is the culprit blocking the drain. However, small lizards or frogs occasionally become lodged in the pipe stopping the flow of the water.  The first step that needs to be taken is to clear the primary condensate drain to allow the system to drain properly.

     One easy way a homeowner can clear the condensate drain is to vacuum it with a shop vacuum from the outside of the home.  The condensate line can be vacuumed by placing the vacuum hose on the discharge of the condensate line.  An empty shop vacuum should be used for vacuuming the drain line.  This way after vacuuming, the vacuum can be inspected for the debris that was removed.  The vacuum hose should be left on the line for approximately two minutes.  After the time has passed, the homeowner will remove the hose from the line.  If the obstruction was sucked out, the drain should start draining on its own allowing all the water that was blocked in the drain pan of the air handler to flow out. 

     If the vacuuming technique doesn’t remove the obstruction, another way to clear the drain is by back flushing the drain with a water hose from the outside of the home.  The homeowner must take care when back flushing the drain to not flush to much water into the air handler causing it to overflow.  A few one to three second flushes applied to the discharge of the drain is usually enough to break the blockage loose.  A large flow of water, most of the time colder than the tap water, will signify the unstopping of the drain.  Once the blockage is dislodged, the debris should flow back out the drain with the water that was flushed in.  If the homeowner does not observe any debris or algae flow back out the drain after flushing, the blockage may have been pushed into the drain pan inside the unit. The debris may drain from the air handler and cause no further problems, but there is the possibility that the drain could become blocked again until the debris is removed from the drain system. 



  The next step should be resetting the float switch. The float switch may be installed in a few different places.  If the air handler is installed vertically, most of the time it is installed on the front of the air handler itself next to where the primary condensate drain exits the unit.  Most float switches have a float with two wires coming from the top of it where the float can be removed from the fitting.  The water needs to be removed from the fitting that holds the float by either turning the float up or over to allow the water to flow back into the air handler’s drain pan. If the float switch is glued in place, the water can be sucked out with a shop vacuum by removing the float and then sucking the water out.  If no water is left in the float switch, the water will have flowed out by itself just by unstopping the drain.

    If the system is installed horizontally, the float switch should be installed on the emergency drain pan located underneath the air handler in the attic or suspended in the garage. The water in the emergency pan will have to be removed to reset the switch. The best way to remove the water is with a shop vacuum. With a shop vacuum suck the water out of the secondary pan to a level low enough to allow the switch to go down to its lowest position.

     Once the water level is low enough for the switch to reset, the system should come back on.  Depending on the system’s components there may be a five-minute time delay before the air conditioning system restarts.  From this point the homeowner should monitor the primary drain to make sure that it is draining while running; and if there is an emergency pan, make sure it is not filling back up with water. If the system trips the float switch again or does not start draining, the homeowner can try the above instructions again.

     If the drain is consistently stopping up, or does not start draining it is recommended that a service technician come and service the system. There could be a problem with the drain line or a problem with the air handler’s drain pan. A professional diagnosis or cleaning is most likely needed for the system.


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Below is a condensate drainline with a large amount of blockage.

Blocked Drain




Tags: ac drain, air conditioning drain line, drain, float switch, stopped up AC drain, unstop drain
Last update:
2017-09-05 01:20
Average rating: 5 (8 Votes)

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