HVAC drain problems....

[STX_Shooter]

Compressed air and put a towel over the sink. I learned the hard way I had junk sprayed all over my restroom.

[Hoss163]

The best thing to do is install a pump to make sure the water always pushes it self out . But get the glog out 1st then install the pump so you want have the problem again.

[trophyhunter01]

Or run a fish tape down it should not be a heavy blockage. When I did mine found some copper tubing scraps they installer dropped down the drain pipe. Also where mine hooked into a sink line for the drain the Y pipe had a really small hole and got the one for a dishwasher drain. No problems since. Good luck.

[wow]

X2 On the fish tape. Both of our houses drain to the washing machine drain.

[Bazo]

I use one of those hand rooters you can get at Walmart for running down pipes to clear them out. Worked on mine.

[SabreKiller]

I'll crawl up there again this evening. When its hot of course! LOL! I'm pretty sure the line runs to the kitchen. I can see it headed that direction and I'm pretty sure that's why they put the P trap in the line.

[double bogey]

Most likely they put a p trap in the line because the connection is under negative pressure. The p trap is to break the vacuum and allow the water to drain out. if you have a heat pump, or electric heat this is the case. If you have gas or propane, the drain connection will be at positive pressure, and a trap is not required. I don't care for p traps in a positive pressure system, due to the fact that lots of clogs occur in the p trap.

As noted, a/c drains are connected to the sewer system at a sink or washing machine, before the sink or washing machine p trap. They cannot be directly connected to the sewer system, as the small trap will dry when the a/c isn't being used, and sewer gas could be drawn into the living space by the system fan, especially in a negative pressure system. (at least this is the logic I apply for this part of the code)

Code now requires a float switch to be installed to shut down the a/c to prevent water damage when lines are clogged.

[Mambajeep]

I had this problem once a few years back. A cup of bleach every time I change the filter, no more problems

[dustoffer]

Any HVAC folks on here care to comment on using bleach? Our company recommends against it as their opinion is that the fumes corrode the unit. They recommend vinegar.

[HoustonR6ryda]

Thank You to the OP for this I forgot about mines-dropping a cup of bleach down the PVC
vent pipe tonight

[SabreKiller]

Ok, I found that the main drain line connects to the 1/2 bath sink vent line up in the attic. I have blown through it and it seems clear. I poured bleach down the line and we can hear it running down the line. The emergency drain pan is still half full though and is draining out through the soffit like it’s supposed to. There is a lot of condensation dripping into the pan. Should I pull the panel off and look in there to see where it’s coming ing from?

[double bogey]

Where is it dripping into the pan from? the drain pipe, or the side of the unit?

[SabreKiller]

It appears to be coming from the side of the unit.

[double bogey]

If it is coming from the side of the unit, it isn't getting in the main drain. Make sure the trap at the unit is clear. Is this a very old unit? You could have a drain pan with holes in it, ( I have replaced several systems in the last couple of years for this reason), or you could have airflow causing water to come off the coil and miss the pan. Air turbulence will also cause water to blow out of the pan. if the trap is clear, you may need a pro to get involved.


There are mixed answers on bleach in the drain. If I had metal drain pans, I wouldn't want bleach near them due to corrosion. Water treatment people have told me that the stuff that grows in the drain line isn't algae, so bleach may not be effective. But a lot of the condensate pan treatments are chlorine based. I can tell you it looks like snot.

[trophyhunter01]

Yep, could be older unit and evap pan is rusted out