A/C Condensate Pump Overflowing

Old 07-08-14, 10:39 AM
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A/C Condensate Pump Overflowing

Hi all! I've already been through many threads here on this topic hoping to fix my issue, but no luck yet.

This issue is with my 2nd (middle) floor air conditioning system, which is connected to a condensate pump (a Little Giant 554401 VCMA-15UL, 115V-60Hz). The condensate pump will seem like it's working fine, but then I'll check it an hour later and the pump's reservoir will have completely filled with water and will be overflowing, even though the pump will sound and feel like it's running.

The pump seems to run fine when I take it off and check it. The float triggers fine and water will shoot out of it. The pump is only about 1 year old. There is no crud buildup in the machine. There is also no crud buildup in the line -- to be sure, I hooked up an air compressor and blew the line out several times, and I even flushed cleaning solution through it to be extra sure.

When I hook it up and fill it to test it with an empty drain line, here's what seems to happen:
1. It works fine for 20-30 seconds, quickly pumps the water up the tube and out of sight.
2. Then if the reservoir is kept full, the pump will continue to run but it seems to slow down -- way, way down, taking a full minute to result in a barely noticeable drop in the level of water in the reservoir.
3. Then at some point it seems to work ok again, draining more quickly, until the float sensor turns it off.
4. After it turns off, there is usually gurgling, and air will make its way into some of the drain line. However, I have looked inside the reservoir when this happens, and it doesn't seem like it's caused by water rushing backward into the reservoir (which I would think would mean I should replace the check valve). If anything, perhaps air is flowing through the pump into the line.

This fact might be significant: The drain line from the pump has a significant rise, something like 20 vertical feet, followed by 15-20 foot horizontal run before a 40-50 foot drop down to the exterior drain. This worked fine last summer, but this past spring they replaced the condensate pump (the last one's motor was shot), and I don't know if my current model is the one that worked last year.

So any ideas what is going on? My suspicion is that it has something to do with vacuum/physics, like something in the way the system was installed, with so much vertical rise, followed by such a steep drop there is some kind of negative pressure or something going on keeping the pump from pumping out all of the water. Or is this simply a matter of my hvac company installed a condensate pump that is just too weak to pump that kind of vertical height?

Any ideas/advice would be hugely helpful!!
Old 07-08-14, 12:03 PM
Join Date: Jul 2008
Location: Kansas
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I think that pump is only rated for a 15' rise. I'd look into tapping into a sewer line closer or a higher rated pump.

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