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Roof AC not draining in roof tubing to ground


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Need some help.  I’m at the end of trying all I know to do.  I’ve confirmed the AC condensate drains are working and running into the hose to the ground (the one embedded in the roof and side wall eventually exiting on the roadside front).  I’ve vacuumed and confirmed the hose from roof to ground is clear.  I have also run water from the ground via the hose up to the ceiling end. All clear.  After running the AC a few hours with lots of condensate water in the hoses (and on the rooftop cause it’s not draining), the water does not travel from the AC down the hose, all gets backed up in the roof cavity where the connections are made.    I disconnect the AC drain hose in the ceiling and water comes out of the [roof to ground hose] like there is back pressure, bout the pressure of a water fountain.  For some reason the gravity head pressure of the AC drain height is not enough to push down through the [roof to ground] hose.  At this point I’m thinking the [roof to ground] hose must have a hump in it where the condensate water must go uphill.  If that’s the case, I guess I have to just live with it as the [roof to ground] hose is embedded well into the roof and sidewalks.  Anybody have any other thoughts?  Possibly some type of vacuum is being created?  Thanks in advance for any ideas, Bob…

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The catch cups may be plugged.  These have fairly small holes and can clog pretty easy.  Even if you blow back up through the tubing the "stuff" is still in the catch cup and will eventually clog the holes. 

When I replaced the gaskets on my AC's in 2020 there were quite a bit of stuff in the cups, particularly stink bugs.

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I've cleaned the A/C drains out on our coach.  I disconnected the hose at the T fitting under the middle A/C.  I then blew compressed air backwards from the ground up to the T fitting.  I also blew air from the top to the ground just to make sure it was cleaned out.  

On another coach I had an A/C drain hose that was burned behind the propane refrigerator.  I had to cut out the burned portion and patch it.  

If you can easily blow air both ways it should eventually drain even if there is a loop in the hose.  Make sure the drain cup is properly sealed to the base of the A/C and there are no kinks forming when you drop the A/C unit back down into place.  

Good luck!

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Have Carrier ACs and had the same problem twice.  First time it was something in the drain hose...disconnected hose at inside connection and used compressor set at very low pressure and blew out the obstruction.   Second time was found when I was doing my once in awhile fin cleaning.  Popped the plastic cover hiding the condesate catch basin...gross junk found and removed.  A pain but if on the roof for something else, good idea to pop the shroud and clean the unit.

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Thanks for all the ideas and input.  After confirming I do not have a clogged line, I’m pretty sure the line has a loop or droop.  I put together a small sump to collect the AC condensation water with a small auto sump pump and installed in ceiling cavity.   DC powered on a 7.4v li-po battery (I use these in radio control airplanes), the pump is coming on every 2 hours and takes about 7 seconds to drain the container.   The pump comes on at 2.5” and off at 1/2”.    Water tight sealed so in case the pump does not work the water will back up and drain onto the roof.  Works great, has good pressure but not too forceful.  Thx, Bob….

 

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