# Hvac drain line problem / question



## countrygurl (Dec 23, 2002)

we had a new hvac system (5 ton ac n heat pump) unit professionally installed last year. 
3 times so far this summer the unit trips because the drain line sensor cup fills up with water. had the company that installed the unit come out the first time they tried telling me the line was clogged, which I didn't agree with because our old unit 17yrs never did the old unit just had a PVC line run straight out the side of house. 
the new unit drain line has a ptrap all new drain line when they installed unit. the new drain line is about 15 feet to ptrap and has about 5 elbows in it. I don't understand why the line is not draining. it seem that it takes about 3 weeks of condensation to build back up from ptrap back to unit where sensor cup is. Amy ideas why this is happing


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## hunter63 (Jan 4, 2005)

Sound like way too many places for a clog to form....lines should be a straight as possible.
May also be a venting problem.
If you may need a condensate pump. 

If there still is a problem...
You need to make yourself a PITA to the "Pros' that did the work....if they blow you off......lawer as small claims court 
Sound like way too many places for a clog to form....lines should be a straight as possible.


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## countrygurl (Dec 23, 2002)

almost positive it not a clog, like I mention drain line and ptrap was put in new with unit, the old unit's drain line never clog it was 17 yrs old. my research says it has to do with negative / positive pressure


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## farmrbrown (Jun 25, 2012)

countrygurl said:


> almost positive it not a clog, like I mention drain line and ptrap was put in new with unit, the old unit's drain line never clog it was 17 yrs old. my research says it has to do with negative / positive pressure


I'm not an HVAC guy, I'm sure there are members who are, so be patient and check back.
However, I noticed you said the P trap was 15 ft. from the pan. Assuming it's run downhill (double check with a level regardless) the vent for the trap needs to rise at least 2 inches ABOVE the pan level to work properly. If that was overlooked, it might be your cause.
http://hvac-talk.com/vbb/showthread.php?1179141-How-quot-not-quot-to-install-a-condensate-drain-line

Also if those elbows are how they fabricated the trap in the field, that may be contributing some as well, since it isn't a smooth flow like a curved P trap.


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## hunter63 (Jan 4, 2005)

Regardless....They should stand behind their work.....
How a job is done in not your problem...they need to finish the job....you paid for.....
I retired for the HVAC-R trade 10 years ago.....Service Guy.

Most likely you are having a pressure lock up, not allowing the water to flow after a while......
Had a few like this....cure on *THAT JOB* to drill a hole in the highest spot on top of the trap.....or it will not flow.
Another was cause by a blower moving too much air...and sucking condensate back into the unit....Needed different pulley and belt on blower.

I say "That Job" as you never know and really don't want to hazard a guess...without looking at it.

Not your problwm...Get on the phone and bytch, bytch, bytch...tell your friends ...do your FD thing.....
But if you paid them money....they need to make it right.


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## Cabin Fever (May 10, 2002)

We had a similar problem with condensation drainage from our furnace when it was brand new. The installers came out and said they fixed it. What they did was drain the water manually so the furnace wouldn't trip. A couple days later the furance was tripping again. I could hear the water gurling/whishing when the furnace's exhaust fan came on.

What I did was got out the installation directions and found that the condensation trap had to be "primed" in order for it to drain properly. In our case, the trap was a plastic box attached to the outside of the furnace. So, I followed the directions and primed the trap. Condensation water drained fine after that.


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## NRA_guy (Jun 9, 2015)

Make sure the trap is vented correctly.









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## oldtruckbbq (Aug 8, 2016)

A


countrygurl said:


> we had a new hvac system (5 ton ac n heat pump) unit professionally installed last year.
> 3 times so far this summer the unit trips because the drain line sensor cup fills up with water. had the company that installed the unit come out the first time they tried telling me the line was clogged, which I didn't agree with because our old unit 17yrs never did the old unit just had a PVC line run straight out the side of house.
> the new unit drain line has a ptrap all new drain line when they installed unit. the new drain line is about 15 feet to ptrap and has about 5 elbows in it. I don't understand why the line is not draining. it seem that it takes about 3 weeks of condensation to build back up from ptrap back to unit where sensor cup is. Amy ideas why this is happing


At least yours has a p trap. We moved into a newly renovated house with a fresh septic system. We were the first ones to use the toilet. After a few weeks, we were burning candles and trying to figure out why the house smelled like sewer gas. My wife just swore it was the sump pit in the basement so she poured bleach in it almost daily. There was no smell in the basement, just upstairs. I finally figured it out - the handyman who did the plumbing installed a 1" line that was open and the AC condensate dripped into it. At the other end it was tied into the 4" sewer line with no p trap. It took just a few minutes and about $5 to correct that and improve the way the house smelled.


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## mreynolds (Jan 1, 2015)

I can recall a job once we had this problem. But ac company too with skilled people. 

There are two holes near the drain. One had a black plug and one red. One of the drain and one is the overflow. Someone had taken the plugs out and reversed them. They installed the drain into the overflow hole instead. Filled up the pan and shut off. Took them two weeks to find the problem because it was so simple. 

Not saying that is your issue but may all them next time they come by to check it. I think NRA guy has the answer though.


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## NRA_guy (Jun 9, 2015)

Why is your P-trap so far from your unit? All I have ever seen were right at the unit. 

As I recall there are 2 types of fan coil units (evaporator sections): "blow through" and "draw through".

That refers to whether the evaporator coil section is past the fan ("blow through") or before the fan ("draw through").

Blow through units pressurize the condensate drain slightly; so they drain better.

Draw through units pull a slight negative pressure on the condensate drain and that can cause a unit to not drain well.

Draw through units need a deeper P-trap to ensure that the condensate drains from the unit.

But can you just reroute the new condensate drain the same short way your old one was routed? 

PVC pipe is cheap and easy to work with. Your 15-foot long condensate line may have a sag in a horizontal run that actually creates an additional trap in the line. If so, you will have air trapped in the line (an air lock) between the traps, and that will cause poor drainage. Unless the line has a nice, continuous downward slope, that could be your problem.


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## Bront (Jan 26, 2021)

countrygurl said:


> we had a new hvac system (5 ton ac n heat pump) unit professionally installed last year.
> 3 times so far this summer the unit trips because the drain line sensor cup fills up with water. had the company that installed the unit come out the first time they tried telling me the line was clogged, which I didn't agree with because our old unit 17yrs never did the old unit just had a PVC line run straight out the side of house.
> the new unit drain line has a ptrap all new drain line when they installed unit. the new drain line is about 15 feet to ptrap and has about 5 elbows in it. I don't understand why the line is not draining. it seem that it takes about 3 weeks of condensation to build back up from ptrap back to unit where sensor cup is. Amy ideas why this is happing


My condensation drain is so simple..moisture drips down from the evaporator coil

into a pan with a flex tube attached for draining..The tube hangs at a downward angle to

where it exits the foundation...around where the condenser

sits...Lennox..installed a few years ago...


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