AC drain line question.

[Goldeneagle]

Went and blew my drain line out to get ready for ac season. This unit was put in two years ago and I'm wondering. Is this P trap required or necessary? If I pour vinegar or bleach in the vent stack, it has to fill the P trap up first. The unit before didn't have one. I'm not sure I like the idea of condensation having to fill up the trap before draining.

[Walker]

Mine doesn't have a peatrap. Now if the drain line connects to your sewer line it needs one to keep gas from coming in.

[S-3 Ranch]

the purpose of the condensate drain trap is usually to stop conditioned air from being blown outside.
is what I read

[Goldeneagle]

Mine doesn't have a peatrap. Now if the drain line connects to your sewer line it needs one to keep gas from coming in.

The line just exits out of the slab in the flower bed. It also looks to me it is in the wrong place to stop sewer gasses. The trap is between the unit and the vent pipe.

[Walker]

If it runs straight outside snd is not connected to anything else then you don't need a p trap

[Goldeneagle]

Sorry for the crude sketch, but if you straighten it all out, it is plumbed like this. I don't think the P trap is serving it's purpose.

[jdavidson]

Now for the correct answer ( not being a Richard )… You have a gas furnace system…
You have a POSITIVE pressure drain system…therefore no trap is necessary. And this is because your evaporator is on the discharge side of the blower.
If your system was electric the drain would be on the suction side of the blower thus creating a NEGATIVE pressure drain system. Then you would need a trap

[BlessedVeteran0305]

Not sure why the person that installed it added a p trap but it really isn't necessary. According to your drawing it seems like condensation could sit in there after the summer months and create build up, therefore creating more work for you or whoever you hire having to clean it out.

[jdavidson]

Not sure why the person that installed it added a p trap but it really isn't necessary. According to your drawing it seems like condensation could sit in there after the summer months and create build up, therefore creating more work for you or whoever you hire having to clean it out.

To be clear…a trap is ABSOLUTELY necessary in systems where the evaporator is on the suction side of the blower (almost all electric heat and heat pump )
But on the vast majority of gas heat applications the evaporator is on the discharge side of the blower and no trap is needed.

Think like this…if the drain is on the suction side,then the blower is literally sucking on the drain opening.
If the the drain is on the discharge side,then no suction occurs on the drain opening…actually the opposite occurs and A VERY SMALL amount of conditioned air goes out the drain along with the water.

[BlessedVeteran0305]

So is his evaporator on the discharge side or is it on the suction side?

[jdavidson]

So is his evaporator on the discharge side or is it on the suction side?

Discharge

[Goldeneagle]

Now for the correct answer ( not being a Richard )… You have a gas furnace system…
You have a POSITIVE pressure drain system…therefore no trap is necessary. And this is because your evaporator is on the discharge side of the blower.
If your system was electric the drain would be on the suction side of the blower thus creating a NEGATIVE pressure drain system. Then you would need a trap

Yes, it is a gas furnace as was the previous unit. So is it OK if I cut out the p trap and go direct to the drain? Previous unit did not have a p trap.

[jdavidson]

Yes, it is a gas furnace as was the previous unit. So is it OK if I cut out the p trap and go direct to the drain? Previous unit did not have a p trap.

yes sir it is absolutely ok to remove that trap

[fishfeeder01]

I had heard that vinegar is safer than bleach due to the possibility of the bleach causing damage to the coils of the system. ??? I have no idea how that could reach back that far, for a drain line, but just putting it out there. I also recommend checking the outside drain location to make sure it is draining correctly, I had water clogged up before and ended up with water under the floor, squishing out as you walked by. huge mess to clean up.

[Txhunter3000]

I have heard the same on the bleach. I have my drain set to where I can take it apart right before the vent and plug the end and then shoot air down the vent. I also have an electricians wire pull reel that I run up from the outside to break it up what'sin tge pipe. It's amazing after blowing it out with air and then running the wire the amount of crap that is still in there.