DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > AC drain pipe question

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Old 08-02-2010, 11:45 AM  
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Default AC drain pipe question

I've resently cleaned the gunk out of my AC unit drain pipe and the unit is running just fine again. To get to the clog, I had to cut into the existing PVC pipe and repair it afterwards.

The original PVC drain pipe had a shallow trap (not like a U trap on the sink, but much more rounded) between the AC unit exhaust port and the clean out "T". I'm thinking of replacing the drain pipe with newer PVC and I'm wondering why there is a trap there at all. It seems that the flow would be much more efficient without any small dip and incline as it exits the AC unit. Can anyone tell me what purpose this trap serves? It seems to me that it's just another low spot for further gunk to build up and it makes using a snake even harder. Do I need this trap or can I just replace it with a straight section of PVC?

Thoughts and comments appreciated. Thanks!

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Old 08-02-2010, 02:44 PM  
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Depending on how long the horizontal pipe run is until it reaches the vertical fall of the pipe, you might need it to prevent condensate from being sucked back into the system via the airflow of the blower motor.
Mine comes straight out the unit and immediately 90's into the vertical drain so there's no chance of it being sucked back in.
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Old 08-03-2010, 02:45 PM  
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Thank you for the insight. There is a 6" run coming out of the unit to a horizontal 90 degree elbow and then about a 2.5' run to the 90 degree elbow on the top of the vertical drop. I guess if I can find a similar PVC trap then I might as well replace it. If not, then I will just use the straight pipe. Thanks again.
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A/C drain line, drain trap

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