condensate drainage problems

hello gents, got a ahu thats leaking condensate, this is the situation. condensate from the evap coil wont run down condensate drain line because the supply air fans seems to be pulling on this water and by intrainment depositing it further along the duct work where there is no drainage and so it leaks where it can. what i find is if i turn the supply air fans off water drains quite freely down the condensate drain or the same thing happens if i open the filter asscess hatch down stream of the evap coil. note the problem is not the condensate drainage pipe work. any help would be great.

Is it a U trap? Maybe its not low enough?

Are the filters clean? Any return air obstruction?

Was it like that from the beginning or is it new problem?

Few things to check,

Is the coil clean?

As chemi-cool said is the u trap correct?

On the return air ductwork Is there anything else tee'd in to it?

I had this a few weeks back in a restaurant and found they had tee'd into the return ductwork a kitchen dishwasher.

you need to fit a p trap and fill it with water

I think if the drain pan is on the sucky side of the fan it needs a p trap (which will need priming), if its on the blowy side it doesn't want one.

had something like this 2day,ended up the filters were plugged solid and that created a vacum inside the unit,causing the water 2 splash round with the fans goin. replaced the filter mesh and that sorted the problem..

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Originally Posted by aircool

had something like this 2day,ended up the filters were plugged solid and that created a vacum inside the unit,causing the water 2 splash round with the fans goin. replaced the filter mesh and that sorted the problem..

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Yep if the filter is chocked up, it will cause a vacum the other side of the filter which is all the coil etc, make sure the filter is clean and again check the U trap is in the correct position, it does matter!

Also make sure that the trap is full of water otherwise it will never work.

thanks for all the responses, the traps and filters are all ok, what i find when system operating is the condensate water in the condensate pan is pulled by the suction of the supply fans to such a degree that the water is kept away from the drainage pipe almost lifted out of the tray. when an access panel is opened up stream then the water flows down the trap quite freely.

Your trap on the drainage line should be close to the drain pan and at least 150mm deep then the drain should fall away from the trap. If you have a large static pressure on the fan the drain line may need to be larger than 20mm diameter

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Originally Posted by mr saw

thanks for all the responses, the traps and filters are all ok, what i find when system operating is the condensate water in the condensate pan is pulled by the suction of the supply fans to such a degree that the water is kept away from the drainage pipe almost lifted out of the tray. when an access panel is opened up stream then the water flows down the trap quite freely.

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You say that traps are OK but they don't seem to be working.

Check the static pressure at the trap inlet and ensure that the trap is deep enough.

Something on the inlet side of the fan is blocked to have increased the suction pressure from what, we assume, was a working drainage system.

Blocked filter, collapsed filter, dirty coil, fire damper dropped, inlet grille damper closed etc.

the evaporator coil did have a carpet layer of dirt which has been clean, thinking about it the coil would really need a deep clean because internally it is still floud to a degree. thanks chaps...

The Fresh air intake louver will normally have a bird wire screen behind it, which can get clogged up after a while. Maintenance deals with filters but can miss this one.

Might be worth a check if all else looks okay on the suction side of fan.