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central air drainage line not draining properly

My AC line continues to stop draining and the AC unit cuts off because the pan is full of water. I ahve had 2 AC companies and 2plumbing companies. The plumber has cut the line in several places because he thought it was clogged. However, through investigating, the line was not clogged, but the water remained in the pan and about 12-18 inches in the line. When he moved the line by picking it up slightly the water drained. I have had to go through this so my times that I have just about melted away because the attic is so hot right now. The plumber now recommends re-routing the line. I would have this done, however I don't want this to happen after I've spent a lot on money. It has worked for 12 years and I didn't have any problems. I have to leave it on 75 because if I raise it to 78 the pan starts to fill with water again. By the way, it is an old house that has been renovated. The line is vented to the gutter with a downspout.I think the plumber and AC people are perplexed. What seems to be the problem?

Re: central air drainage line not draining properly

I had a similar problem this Summer . The drain on one of my units kept backing up and filling the pan until the float switch turned the unit off . Mine was plumbed into a vent stack and had a small P - trap that kept clogging up . Since the unit sits on the joists , it's very easy for the drain line to get elevated just enough to prevent the flow of water . Make sure you have a downward slope to the line and that it's not clogged or restricted in any way . Does the drain line have a little vent pipe sticking up ? Gotta have that vent for gravity to do it's thing . You would think a plumber and an A/C man together could figure something out .

Re: central air drainage line not draining properly

make sure the drain line is trapped as it leaves the pan and that the outlet is slightly lower than the pan

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