A/C Evaporator Coil Question - http://www.hvacmechanic.com/ Forums
Original message
| walrus
 |  "A/C Evaporator Coil Question"
, posted Mon 16 Jun 23:12  
I posted this one in the general discussions forum. Probably should have posted it here since it is a residential A/C question.
The overflow pan for my A/C is catching condensation instead of it going down the drain pipe. Clogged drain pipe right? Wrong. I poured some liquid drano and about two quarts of hot water down the drain pipe. Away it went. I opened up the evaporator coil cabinet. Conformed both pipes (drain and overflow) clear. Well, overflow is obviously clear because that is the way water is being drained. I plugged up the cabinet side of the drain pipe and blew down the top of the T and the water in the trap blew right down the drain. The coil lays in the shape of a V. The channel on the right side of the V (where water is supposed to go out to drain has condensate in it. But so does the other side which leads to the overflow pipe. I found a rubber plug laying loose inside. I have no idea where it goes of if it is related to my problem. The unit is 13 years old, making cold air (15 degree drop) although there is evidence of some rust on the outermost portions of the coil. I'm not going to try to remove the coil. That's call the professional time. But I thought I would ask if there is something obvious I can do. Any ideas? (Lennox air handler laying horizontally in attic.) Thank you for any information you can provide.
walrus
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Replies:
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| answer
| "Re(1):A/C Evaporator Coil Question" , posted Tue 17 Jun 09:04:
OK drain 101.
-Water does not run up hill, is the unit sloped towards the drain or at least flat? Is the drain line straight and sloped thru the attic?
-Double trap. the P trap or dip in the pipe is for proper drainage(if you have a gas furnace it may not be needed) However if there are 2 traps i.e. a real one and another belly or non supported section of pipe, even under the house the drain will vapor lock and no flow unless forced or water poured in. Remedy put in a vent with a "t" and a stack in the drain after the p trap.
-Blockage in p- trap and/or at termination.
-Installed by duct monkeys, Lennox I think has drain holes on both sides of the horizontal pan are the holes on the far side blocked? Remedy dry and get a tube of silicone and a small vinyl hose for the silicone tip and fill them.
-Drain of secondary drain on the front of the unit is too open or not the right drain hole, hook up drain to one hole the lowest and leave highest to drain to emergency pan.
- Dirty filter causing extra suction from the fan makes the drain line into a straw and sucks the condensate in.
- Ice on evaporator coil from other malfunction, ice does not always melt into the drain pan the way we would like; it can miss the drain pan.
Be good to your fellow man not nice there is a difference.
[this message was edited by answer on Tue 17 Jun 09:12] |
| answer
| "Re(1):A/C Evaporator Coil Question" , posted Tue 17 Jun 09:04:
Be good to your fellow man not nice there is a difference.
[this message was edited by answer on Tue 17 Jun 09:05] |
| | walrus
| "Re(2):A/C Evaporator Coil Question" , posted Tue 17 Jun 18:33
The drain runs fine. The condensate is accumulating in the coil box and eventually coming out the overflow. The normal discharge tube is clean all the way to the drain. The normal discharge tube and the overflow tube are horizontally side by side at the same level. I talked to a friend who said he tried to fix a drain catch pan with epoxy and a week later it leaked again. He said that those coils and drain pans just rust out (especially after 13 years) and the solution is to have a new coil put in and have the system recharged. Make sense?
walrus
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| | theduke03
| "Re(3):A/C Evaporator Coil Question" , posted Tue 17 Jun 21:27
Where is that T in relation to the trap? If it is before the trap then that could cause your problem. Can you take pictures and post them here by uploading them to photobucket.com? Click on IMG code to copy it, then paste code in your reply.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(4):A/C Evaporator Coil Question" , posted Tue 17 Jun 22:13
I've narrowed the problem down. The sewer drain is fine from the output of the coil through the Tee down the P trap and to the city. Lennox puts the drain and overflow drain at the same height horizontally opposed in the cabinet. The difference is that the overflow is on the fin side of the coil (facing the house ducts) and the normal drain is on the large copper coil side of the drain (facing the furnace blower). Since there is positive pressure from the blower, I guess the Tee is there to keep it from blowing the condensate completely out of the P trap. I can feel air blowing up out of the Tee and into the attic. I guess I'm air conditioning the attic! Anyway, I verified the coils are clean. So if condensate is on the fin side, I'm guessing that I've got low freon and it is icing on that side. I called the AC guy to come check the freon. The drain problem was leading me in the wrong direction. i thought it was plugged up at first. Then I thought the whole coil must have rusted out. Now I'm thinking I over thought the problem and the problem is lack of freon. What do you think?
walrus
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| | theduke03
| "Re(5):A/C Evaporator Coil Question" , posted Tue 17 Jun 22:25
That tee is for flushing the trap. It can be capped. I think if it was freezing up you probably would have seen ice. Are you sure that the drain is connected to the primary drain connection sometimes labeled with a P ? Not the secondary(overflow) S connection?
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(6):A/C Evaporator Coil Question" , posted Tue 17 Jun 22:56
The primary drain is easy to see. It comes out of the coil, into the P trap with the Tee above and slopes down to join a pipe with a vertical drop of 12 or so feet into part of the house sewer system. I can hear water running down that pipe as I pour it into the Tee. The overflow pipe comes out of the coil cabinet down directly to the overflow pan which is connected to a 15 foot PVC pipe that sticks out the side of the house. The dripping from that pipe is what originally alerted me to the problem. Overflow pan was full. Nothing going down the sewer side. I snaked both PVC pipes. The problem is the condensate chooses to go for the overflow pan instead of the unobstructed sewer line. It's coming from the fin side of the coil.
walrus
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| | theduke03
| "Re(7):A/C Evaporator Coil Question" , posted Wed 18 Jun 00:20
What I'm getting at is maybe those drains were installed backwards? If water drains into the secondary drain before the primary drain then either the drain pan is improperly pitched or maybe the secondary should be the primary? Pictures would be helpful. BTW, both sides of coil have fins.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(8):A/C Evaporator Coil Question" , posted Wed 18 Jun 08:31
I'm confused about the backwards installation idea. The unit has been draining properly for 13 years. Only recently did the overflow start producing water. I naturally thought it was a plugged drain. When that didn't pan out, I looked for answers elsewhere. Maybe the coil itself is shot although I'm getting a 15 degree drop in cooling. It's comfortable except for the condensate problem. I'll try to get picture when I get home from work tonight.
walrus
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| | walrus
| "Re(9):A/C Evaporator Coil Question" , posted Wed 18 Jun 11:58
Also Houston204 said that low refrigerant can cause improper drainage. How does that happen? What are the mechanics of water draining one way or the other based upon refrigerant quantity?
walrus
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| | theduke03
| "Re(10):A/C Evaporator Coil Question" , posted Wed 18 Jun 19:49
A low charge will cause the coil to freeze over. Then the ice will melt and drip around the drain pan instead of into it. Normally(no ice) water will cling to the coil and run down to the drain pan. Ice will also plug the drain connection thus resulting in an overflow.
What I don't understand is that you say drain is not plugged. You also said that the water goes int the overflow before it goes into primary drain. Primary drain is downhill from the overflow so this suggests that your unit has lost a hangar or something that supports it(level) or supports the drain pan. I don't see any other way that water would bypass the primary drain.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(2):Re(10):A/C Evaporator Coil Question" , posted Wed 18 Jun 23:27:
I've got pictures (.jpg) but don't know how to put them in. I tried copy and paste. Only the words seen below came up. I don't see an import or upload tab. What's the procedure?
plumbing_side_view.JPG
coil_door_open.JPG
overview.JPG
walrus
[this message was edited by walrus on Wed 18 Jun 23:51] |
| | theduke03
| "Re(3):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 02:46
You must first go to photobucket.com Click the "Coose Files" button to upload pics from your computer and select pics. Once uploaded then click on the IMG code under pic to copy it, then paste in your reply.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(4):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 10:40:
Here is plumbing view.
walrus
[this message was edited by walrus on Thu 19 Jun 10:42] |
| | walrus
| "Re(5):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 10:52
Here is overview in attic. Front to back: Plenum,Gas Furnace,Evap Coil,Plenum
walrus
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| | walrus
| "Re(5):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 10:46
Here is coil view. Only right side is supposed to expel condensate. Left side seems to have some leakage. You can see the rust. 
walrus
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| | theduke03
| "Re(6):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 19:11
Well now I'm not so concerned about the way the drain is setup since it's on the positive side. Is there any chance that drain pan is clogged with rust flakes between the 2 drains? You say that water drains away when poured into tee but what about between the drain pan and tee? Could a clog be there?
"My dad was the most feared furnace fighter in Northern Indiana."
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| | walrus
| "Re(7):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 23:13
I forgot to say thank you for the picture posting info. How did you draw those arrows?
walrus
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| | walrus
| "Re(7):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 21:57
I snaked the pipe from the inside of the coil up through the Tee and down to the drain. I just had the A/C service mechanic out and he said I have a slow leak in my condenser coil. (Checked it with a sniffer.) He also said the same thing two years ago. He found the freon to be low. He charged the system. Houston204 said that when freon is low, warm spots form on the coil and the blower blows the water out instead of it dripping into the pan. Man, I was hoping that was the case but no luck. It's still leaking. My A/C guy also said that my plumbing (Tee) was fine but he capped it. I asked lots of questions and he is a nice fellow who didn't seem to mind. He told me that different manufacturers have positive or negative pressure at the Tee based upon where the blower is positioned. I guess he meant that some units blow toward the Tee and others suck away from it. Anyway, my Lennox is positive pressure. So we waited and the leaking resumed. Tomorrow the A/C guy is going to clean the coil and pan. He said if that doesn't work, the coil will need to be replaced.
walrus
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| | someheat
| "Re(10):A/C Evaporator Coil Question" , posted Wed 18 Jun 19:37
You say you can feel air coming out top of tee. That is an indication that the trap and tee vent are backwards. On most systems the drain pipe should come out of the coil and down into a p trap then vented with a tee fitting. If your trap is full of water, no air should exit vent.
Just my two cents.
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| | rayjones3
| "Re(2):Re(10):A/C Evaporator Coil Question" , posted Thu 19 Jun 12:56
I agree!
See also "theduke03" reply of Tue. 17 June which also suggests this.
Cap the existing "tee". Then install another vent "tee" DOWNSTREAM of the existing P-trap in the primary drain line.
Ray Jones
rayjones3
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| | sbrooks157
| "Re(3):Re(10):A/C Evaporator Coil Question" , posted Fri 20 Jun 16:31
I agree its piped wrong , vent tee should be after p trap,Also can p trap secondary and bring trap to with in half inch of top of condensate pan... this should elevate problem....my 2 cents.
worth a try, pvc pipe cheap cheap!!
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| | walrus
| "Re(4):Re(10):A/C Evaporator Coil Question" , posted Sat 21 Jun 17:29
My friend the A/C tech and a buddy of his poured about a gallon of water into the coil pan to observe what was happening. I heard one guy say, "There's an obstruction". Then they poured about a gallon of bleach into the pan. He said it was "eating up" the goo that was in there. Then the unit was turned on. So far so good. No overflow. But there has not been any major condensate discharge either. I just opened up the coil door to take a look and the pan was moist but not full and the coils were sweating. Maybe it's not humid enough for there to be an accumulation or maybe the positive pressure from the blower is pushing it out. I'm getting a 17 degree drop in temperature between two thermometers, one in the return and the other in the nearest duct.
I also learned how Lennox is able to put two drains (normal & overflow) at the same height in the horizontally positioned pan. The overflow pipe has a lip on it that blocks the lower half of the pipe.
So now I wait and see (and worry). That's the hardest part. I keep going into the attic looking for trouble and hoping not to find it. If anything further develops, I will post it.
Thank all of you for your help!
walrus
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