[markrun330]

The other day we had the Air Conditioner guy out to fix a problem with some water dripping through the ceiling from the air handler. I told him there was no water coming out from the AC overflow drainpipe and he told me, no, that wasn't the AC drainpipe but rather the drainpipe from the pressure relief valve from the hot water heater. To prove it, he opened the hot water heater's pressure relief valve, and sure enough out came water from the drainpipe in question. So far, so good. A half an hour later, while he was still working in the attic with the AC, we heard a whooshing sound, like a large suction action from a huge vacuum cleaner. Later on, I went into the bathroom and the bathroom sink was coated with a heavy thickness of sludge, with some spillover on the floor. It didn't seem to be sewage--no real smell associated with it--but appeared to be scale from metal pipe. Our bathroom drain pipe is PVC, I might add. My questions: (1) What caused this apparent blowback? (2) Could it possibly be related to the AC guy fooling with the hot water pressure relief valve? (3) If it was just a coincidence, what do I need to fix to prevent a recurrence?
I should add this a 10 year old house with some strange builder blunders, like the light switch in the attic controlling the ceiling fan in the den.

[speedball1]

Good morning Mark, I'm assuming the AC air handler and water heater are located in your attic. I'm going to have to question,( big time) the AC guys report to you. Of course if you pop the lever on the T&P valve you will get a discharge out the overflow tube. But where did that T&P discharge terminate? On the floor of your attic so it dripped down from the ceiling or a pipe that ended up out side or in a heater pan? If the drain from the air handler was blocked you wouldn't get a disharge from the pipe, but the condensate catch pan located under the air handler would overflow and come down through the ceiling. Another thing that puzzles me is if he determined the problem was with the T&P valve why was he still "working on the AC" 1/2 hour later? As for the blow back in your lavatory, I can set up a scenario that faults the AC man right along with the AC contracter. If the AC guy was attempting to shift blame from a blocked AC condensate line to a faulty T&P valve for reasons of liability he would then have to clear the blocked condensate line without you being aware of it This is done by shooting compressed air through the condensate line to blow out the clog. If the AC contracter got lazy during construction and instead of terminating the condensate line outside like the code calls for and tied into into the lavatory vent where it would drain into the drainage system instead, when the clog from the condensate line let loose a blast on compressed air would be released into your drainage system and blow all the water in the lavatory trap seal all over the bath room. This is the only way this could have happened. So your left with a dishonest AC man that lied to you to get his company out of liability for any water damage and the AC contracter that didn't follow code when he installed the air conditioning. A simple way to check my theory would be to track the condensate line back. It should be 3/4"PCV that terminates outside. If it ties into anything else then it's out of code and outlawed. The AC contracter should be libel for any water damage and for putting your house back into code and shame on the AC guy for misleading you.. If they give you any static over this you can quote section 1308.8 (Connections) of the Standard Plumbing Code that states in part that, "No direct connection of a steam exhaust, blowoff, OR DRIP PIPE shall be made with the building drainage system." Please keep me in the loop on this and let me know if my theory was correct. Good luck, Tom

[markrun330]

Thank you for your very helpful response, Tom. In defense of the AC guy, I believe he only opened the T&P valve (I believe this is what I was referring to as the "pressure relief valve") to demonstrate to me that the drain pipe I pointed out on the porch was not related to the AC drain pipe. This seemed to be a conclusive demonstration because water gushed out instantaneously when he turned the valve. Thus, I believe it didn't need to fill up an intermediate drain pan and only then exit on our porch. And I should have clarified that he did this when he first arrived and hadn't been up in our attic at all at this point. Plus, he's telling me I do need a new air handler, so I don't thing he was trying to shift blame to the T&P valve. So, I think he's okay, although your idea about the compressed air to clear the condensate line is intriguing. But wouldn't he have needed a big old compressor to blast the compressed air through the line? All he had up there were some simple tools, not even an aerosol can hidden in his back pocket. Oh, finally, the realtor talked us into buying one of those home warranties, which excludes water damage, so he has no reason to try to weasel out of the bad air handler claim.

Your other point about the AC contractor, however, is cause for some serious concern. That is exactly what I was trying to envision--how to relate two seemingly independent systems, namely, the T&P hot water line and the condensate line. Here we've lived in our house since March and have had no problem with blowback till the day the AC guy shows up and throws the T&P valve just to demonstrate to me what the porch drain pipe was connected to. It just seems like too big of a coincidence to not be related. I will go up and check the condensate line right now. It's 90 plus degrees here in Fort Worth, so the attic's not going to be fun.

Thank you for the very helpful information.

[markrun330]

Tom,

Okay, I went up in the attic, but it wasn't as clear cut as I had hoped. However, I'm ready to eliminate the T&P line as a suspect. It does disappear from sight, but doesn't seem to be anywhere in the vicinity of the vent lines and drain lines in question. And again, water gushed out so quickly when the AC guy threw the valve, that I think it's okay. I think it's a red herring.

There is indeed a 3/4" exit line from the air handler condensate drip pan which clearly runs outside as expected. But there is also a 3/4" PVC line directly from the air handler itself. This line does not run directly outside, but rather takes a sudden vertical turn downwards in the vicinity of the bathroom drain vent pipe. I can't say for sure that the two lines are connected, but they certainly disappear in proximity.

I'm back to your theory. If the air handler exit line and the bathroom drain vent line are somehow connected, and if the AC guy somehow had a source of compressed air up there with him, and if he tried to clear the line just to be sure, it would blow material from everywhere back down the drain vent line. And out into the sink! I wasn't watching him that closely that I can't say for sure he didn't have a compressed air supply up there with him. What kind of air supply do AC guys commonly pack up into attics? He's coming back to install the air handler. So I'll try to ask him.

Thank you for your help. I feel much better armed to deal with this from our conversation.

Mark

[speedball1]

Hi Mark,  What you need is a definite explaintion as to just where the water came from that dripped through your ceiling and I haven't heard one yet.  If you have please share it with me.  Also what's the problem with your present air handler and why would you need a new one?  The T&P,( Temperature and Pressure) valve has nothing to do with the AC and shouldn't be a factor.  Most Ac air handlers have only one 3/4" PVC condensate drain line from the pan.  What is the function of the second one, where does it originate and what does it tie in to?  I hate to  heavy up on the AC guy but your not getting the answers that you should and now you're going to be socked for a new handler?  I would seriously began to think about a second opinion before I went into a lot of expense.  Somebody isn't being upfront with you and If it were me that would piss me off no end.  I've been a plumber for over 50 years and when I tell you the only way for the liquid in a trap to blow back is if someone with a air bottle interjected a blast of compressed air or dropped a cherrybomb down the lavatory vent into the drainage system you better believe me Pilgrim.  You're not getting the whole story  and if you're not then I wouldn't rest  (or kick out any money) until you do.  Regards,  Tom