I've seen a lot of discussion on whether a positive pressure evaporator (like one on top of an upflow furnace) needs a trap or not. While it doesn't cause the drain issue like a negative pressure, it does eliminate air leakage. Please share your opinion on this. I am a HS HVAC teacher and I'd love to know your thoughts.
No matter how many times this is explained verbally, the phenomenon of negative pressure is not usually well understood to most until they see it in real time. This is a terrific demonstration!
@@thejohnbeck lol first its funny seeing such a recent comment to an older video, right in line to what I was thinking as well. But I found the answer. When the system is running and sealed, and the fan in the system is moving air, it is on the input side (in this setup). Meaning its a vacuum, or under negative pressure. The drain is like a straw, so while the fan is on, the drain is sucking in air. (I wrongly assumed in the video that "system running" was focusing more on the temperature of the evap coil since he focused on it). When the fan stops, there's no sucking, and the pressure inside that area and outside are equal so the water is free to move via gravity. The trap on the drain needs to be filled with water or it doesn't work, because the weight of the water is more heavy than the sucking vacuum of the blower motor in that small area, so air cannot come up inside, so the water can move under gravitational forces, without being pulled back into the pan. Real world example. You get a fresh frosty milkshake from wendy's and go to suck on the straw. It's too thick but you kinda try again, but as you give up, the negative pressure in the straw makes your spit backwash into the straw.
My Carrier Infinity runs all day long here in FL and your video carefully explains why my pan holds water and I get the “stinky sock” smell. Thank you for the video.
Thank you !!!! I felt dumb when I first saw a video of someone really cocky because he did understand it. I wasnt dumber i just had to take the time to educate myself. I hope when I go to school my teachers are as good as you.
Thanks so much Luis and make sure to check out the video I just published on does a minisplit need a condensate trap. I get into more detail there, thanks!
When we moved into our new house in North Florida about 8-years ago, we soon started to have filter failures from moisture. This was happening every 1-2 months, and at times the failed/wet filter media would get blown up into the underside of the coils. It was quite maddening. After considerable research, I found a similar video and installed the clear trap you've shown in your video. After that, no more issues. I'm a bit confused why something so critical can be missed by the Building Inspector, and the private Home Inspector that I contracted to check the house out before we purchased it. You've done the best job explaining why the trap is needed, that I've ever seen. Great work!
Ha ha ha. Inspectors. That's a good one. They nitpick little things that don't mean a bit of difference, but anything important they forgot to mention in inspector school. Here's 10 pages of bullcrap that needs to be fixed. Give me my check.
I am HVAC contractor with ~10 years of experience. I think that this video is the best explanation why do you install that p-trap on the condensate line so far. :) Thank you!
Again, well done! Getting this point across to installers that are trying to “just get the job done “is critical. No excuses for not having a trap installed.
@@acservicetechchannel could you tell me why water in the drain tray or pan starts flowing out when the pvc pipe system with water filled trap is attached?
During home inspections I would talk about the vacuum effect when there is no trap. If the unit is in the garage or close to where there might b some chemicals, fumes can be sucked up into the air flow going to the home and if that happens because there is no trap at the condensate line no one will know where the Oder is coming from. So the trap here is rather important!
Good video. And this ONLY applies when the blower motor is on the supply side of the evaporator causing a negative pressure which sucks air into the condensate pan from the drain. When the blower motor is on the return side of the evap coil, you will have a positive pressure pushing air out of the drain hole and you won't need a p-trap for this
Brilliant. I noticed last year when I happenned to look inside my furnace that the condensor pan was completely full and not draining. I could tell there was negative pressure so I openenned the filter area and sure enough it drained immediately. The system was installed by the previous homeonwer so I have no idea of the experience of the originall installer but they clearly didn’t understand this issue. Great explanation and video.
Never realized while the air flowing through the evap is on its way to the cold outlets, it will pull air back through the drain tubing---perfectly logical. The back pull would be untreated air as well. We had our system changed in 2015 and they installed a trap. I thought it was silly. Now I know!!! Thanks for making the video.
Literally could not understand why my furnace was filling up with water until I watched this video. Thank you so much you saved me an expensive service call.
Great demonstration. But this only happens with the coil before the blower. When the coil is after the blower air comes out of the drain pipe and you need a trap to stop the air from escaping. I learned a lot from your channel thanks for the tips!
Thank you very much for clueing me in. That solved the problem of condensate build up in the bottom of my A/C unit. I cut a hole in the piping for easy trap cleaning; I did not realize it receives an internal negative air pressure. I thought it only trapped debris. HAGO; Thanks again!
I just had my unit serviced. Guy at ACE told me I needed a trap (retired HVAC) guy who serviced unit did not install one. I have an identically appearing unit as the one pictured. Anyways guy called days later and now he said he “forgot to install” and is coming back to place one. Just trying to understand the process and this video was awesome! Thanks
Wow! This is what is wrong with my AC! The person who installed my AC kept saying he had no idea what was wrong with my system and HE INSTALLED it. Thanks! Hopefully my hubby can fix it.
Great visual for evaporators on the negative pressure side of the blower. You should explain that not all are on the negative side. An explanation of where to put the vent would also be helpful. In my neck of the woods most residential evaps are on the positive side of the blower.
My exact thought. The plus side of adding a trap on a push coil is you don’t lose some of the efficiency of air being leaked out of the drain, but it’s not critical to have one as it is on a pull coil.
Keep in mind this is for an air handler and not a coil on top of a furnace. The coil on top of the furnace has positive pressure so you dont need a trap.
The Delta p is small, very little air escapes. You can test this just by running the fan or furnace and very little air comes out of the drain hole, even less if you have a drain hose on it.
Thank you for posting. My apartment AC unit was leajing water all over the drip pan,and the EZ trap was bone dry. After watching your video, I opened the trap and filled the curve with water - hopefully this fixes the issue.
I've serviced a package unit witch had a zone board installed (left) inside the blower cabint wich burned out twice .I was ther on the second call, Noticed it was a little damp and the zone board had moister on it, and that they had short 4" pvc pipe off the drain pan. I added a p-trap, installed new zone board called back a month later to make sure clients system was working. Problem solved . Many techs even some hvac business iv talked to think these ptraps are unnecessary but I beg to differ .NICE DEMO CRAIG!
Best ever demonstration! I don't think mine is linked into a trap but it I think the broken humidifier and furnace are linked into the line too. Furnace is under ac unit and has some sort of black box cleanout
Unions in condensate lines aren’t necessary,a simple tee with a cap or a modern float switch has what you need to disassemble without any problems to clean………or best thing I’ve found after over 20years of doing it is a simple shop vac,connect it outside and it will suck all the bs out and then put the cleaning tabs in the evaporator coil pan and your g2g……..or your nitrogen tank with a simple Freon line hose will blow everything out from the inside out.
Very Valuable Information that I was looking for I bought your AC book And I learned A lot, I can't wait Tell I see your book on Furnaces trouble shooting Specially on high efficiencies. On the market.
Absolutely! We put 8 months of work into fine tuning those questions and they are the very ones I would like every tech to know pertaining to the book, thanks!
Great video! There should also be a vent pipe on the left (output) side of the trap you show in the beginning of the video. I remove the red cap on the trap and put the tube there.
Some Carrier AC’s have a built in trap in the Drain Pan, so you need to look and/or check the units literature. It you can’t see directly thru the opening to the drain pan, or from inside the drain pan to the pipe. Then check the literature.
Thanks for such grt explaination, it's very rare that we can see a demo, which you have provided. Requesting if you'll can also provide the maths related to p trap..or thump rule... thanking you.
A B, the higher the static pressure in the system, the more need for a trap there is. You can't go wrong with a deep U trap but in most cases a p-trap will suffice. The biggest thing is making sure that a PM includes the cleaning of the trap or that the building owner is aware to clean the trap one to two times a year, thanks!
Now I know why there’s a P-trap before the condensate pump. Thank you. It didn’t make any sense why a trap was necessary when no sewer gases would get through the condensate pump.
While that is a true point, however, a trap still serves a purpose in a positively pressurized cabinet (or unit), as it prevents the conditioned air from escaping. In terms of wasteful energy, can be compared to why they seal all the seams in the ducting.
Love the video, but one clarification. You only need a trap if the coil is on the negative pressure side of the fan. In the North, most of what we install are a gas furnace with the evaporator coil on top of the furnace. No trap is needed because the force of the blower is positive.
I’ve always puts traps because all the debris that will eventually get clogged will get clogged there and not in the wall or somewhere that is harder to get and then when it clogs a pipe cleaner and bleach is all you need 👏
This can happen on positive pressure units aswell, altough probably not as common. If the drainpan outlet is connected with a hose that is way thinner then the drainpan outlet pipe diameter, the velocity of the air passning makes drainage impossible, at least as long as fanspeed is high.
Have you ever seen a blocked drain line affect a TXV Craig? I was on a call once where the evap coil kept frosting over until the abnormally long, mostly flat, drain line was blown clear. The very moment the drain cleared the frosting stopped.
Frosting would only occur if the sat temp of the vapor line was below 32 degrees. Even if the bulb was submerged in the water, the temp of the water would not restrict the flow of the refrigerant into the evap coil. Very odd. I feel like I am missing some other part or detail, odd, thanks Tom!
The frosting happens because your A/C is constantly pulling moisture out of the air and returning it to that evaporator pan and if the water can’t drain the moisture doesn’t collect in the evaporator pan and then causes it to freeze because all excess moisture is not transferring
Occasionally I see condensate tubing left unglued, I suspect to allow for easy cleaning. What are you thoughts on not gluing a couple strategically selected fittings?
I don't have a trap on my system, but the drain runs well for a 4 ton unit. I suspect when I install this same trap tomorrow I'll pull even more condensate from the unit! And I thought my AC man was top notch... apparently not.
-Do you have what it takes? Quizzes: www.acservicetech.com/quizzes -Our Articles with many descriptive pictures: www.acservicetech.com/articles -Facebook posts every other day! facebook.com/acservicetech
That trap is not always necessary and the reason is that here in Florida, and other areas, houses are built on slabs. The condensate pipe runs down into/below the slab, then runs back up above ground level, usually about 6 to 8 inches high, where the water exits. This causes the "below ground" level of the pipe to fill with water, in effect automatically creating a very long "p-trap".
AC Contractor here in Florida lack great amount of critical knowledge The same way they do not use Nitrogen when soldering cooper lines and not even sanding cooper lines-You always need a condensate P trap -It is in the HVAC exam
@@user-hu4hx6bm6m Yes, but where is it located? The point was if it exits ground level, a p-trap at the air handler/furnace is where you'll see it. If it goes underground and returns to ground level, it's there, but you won't see it as it's formed under the slab, contains several inches of condensate, and prevents airflow from exiting the air handler.
I love those clear EZ trap! Don't like the shallow trap, they dry up in winter, first summer cooling = leak! In that case I make a deep one that can never dry out. Btw In case of positive pressure unit, no trap is required
@@abnergarcia6252 He means that if the blower pushes the air through the coil and not pulls..Blower is beneath the coil. in the video the blower is above the coil.
eddman32 thank you! So in the video the unit is a “negative” pressure unit? Anytime the blower “pulls” from the coil is a negative unit? Very interesting. After this video I found another video on “Expert Express Plumbing Heating....” where he shows the effect of high static in a zone system. And it was a horizontal left unit, but the water was being pushed out of the secondary drain plug.
Abner Garcia. The vast majority of units the blower "sucks" the air across the coil. In the minority are units that are either "ambient" pressure; or blower is upstream so that the air is "blown" ie positive pressure
Mine drips the entire time its on...doesn't speed up when the blower shuts down...My tech added a "chimney" to the "T" that exits the side of the A coil drip pan.. It sucks air over the draining water...
This is a great demonstration. But isn't negative pressure only a thing on draw-through units (aka negative pressure system)? If it is a blow-through or positive pressure system, isn't there positive pressure where the coils are?
This only applies when the coil/pan is in a negative pressure relative to the space, when the blower is sucking air through the coil. Not a problem when the blower is pushing through the coil. I don't think this was explained well or shown in the video. It is better to understand the mechanics so you can diagnose problems versus simply being told blanket statements.
yes, however most air handling units and fan coil units have the fan after the coil, thus you will most usually find the drain in a negative pressure/being sucked when the fan is running.
I agree what you both stated, I'm not a repair tech but install all systems. watch the video again. The filter is in between the coil and the box below i guess the blower compartment . So would that mean the coil is in positive pressure even thought you see it is in negative. What are y'all thoughts. Thanks ahead of time
Good video but the placement of the blower in relation to the coil determines if the condensate drain has a negative or positive pressure. Most systems I have worked on have a positive pressure. A untrapped positive pressure system will blow air out the condensate line and I have had customers on occasion hear a bubbling sound in the walls from this. I experienced a job where an untrapped negative pressure condensate line was hooked up to the houses sewer drain line and without the trap it pulled sewer gas smell into the house. Also an explanation of the secondary drain should be given. When the primary drain becomes clogged, the water will then drain out the secondary instead of leaking into the house. It is code here in California on two story houses to have this secondary drain run outside over a window so the homeowner can visually see this problem. You could also install a condensate float switch in the secondary drain to catch this problem before water damage occurs.
I have a goodman furnace with the blower at the bottom and the ac lines and I'm assuming the coils on the top. My drain plug is on top half way point of the furnace. Will that make my system positive pressure. Because I don't have a p trap.
Right, most systems I've seen are that way also. With the blower below the coil and blowing upward into it, it will create positive pressure - not negative. My system blows air/water out the condensate port - not taking air in. Hence no trap required nor present. This is only an issue if the blower is after the a-coil in the system.
