I have a Tempstar NFCP3600/A1. There appears to be two condensate drains. The main one is plumbed to the outside. There is another drain next to it and it is pointed down and drains into the garage where the unit is hanging. I guess the secondary drain is an overflow drain, maybe not. I have cleaned out the primary drain by using a vacuum. That solved the problem temporarily. There is definitely water draining to the outside from the main pipe. Would you suggest plumbing the two together so they both drain outside?

SOURCE: Drain Problems on American Standard A/C and Heat pump

You have a plastic condensate pan and you could have developed a crack in it. But most likely, there is still something that is clogging the drain. You may need to run a snake through it instead of using air. If you ran a snake through then it's probably a crack. Sometimes the crack can be at the outlet where something might have hit the pipe. Also, if the unit has a "draw through" coil, then there needs to be a p-trap installed on the unit to keep water from being drawn back into the unit while it is running. If it is a "blow through" coil and a p-trap is installed then remove it. The p-trap can restrict the flow of water leaving the unit and the least bit of debris can cause the unit to overflow. Draw through means the blower motor is pulling air over the coils and sits over top of the coil. Blow through means that the blower is pushing air into the coils and sits down below the coil. Hope this helps.

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Make sure that the flexible pipe is securely connected to the drainpan, it can come adrift and cause leaking. The way to check this is to make sure everything is dried out completely. Then open the front grill and carefully pour water so that it goes only into the drip pan. Pour slowly so that you do not overflow the pan. If water is coming out on the outside and you have no leaks on the inside, then you can rule out the perished or disconnected drainpipe theory. In this case your unit may be short of refrigerant causing excessive run time and a freeze up of the evaporator.

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It sounds like the drains is clogged. Clean it and see if that's the cause.

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drain line is blocked water is accumulating and over flowing clean line out

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the drain coming off the unit is the one you need to clear, not the secondary pan. its usually clogged in the P trap which is usaully not far downstream from the outlet on the coil.

Testimonial: "There was no p-trap installed so I decides to cut the pvc pipe six inhes south of the coil. Cleaned debris and replaced drain. All is well.. Thank you"