20 Causes of Low Indoor Airflow on Furnaces and Air Conditioners!

hey guys this is crema clap filled with AC service tech and today we're going over is 20 causes for low indoor air flow for a furnace and for an air conditioning system so low air flow is a big deal and for a furnace the furnace could overheat and for an air conditioning system the evaporator coil could freeze and even if the problem wasn't that bad but you still had a little airflow problem you're gonna have longer run times you're gonna be at a lower capacity and lower electrical efficiency so you'll want to try to figure out what that problem is one of the first causes I want to mention is a dirty indoor air filter so we all know that we want to change these filters out so they don't get clogged up with dust but something I want you to keep in mind is that there may be multiple filters in the building so you want to look inside the building to make sure if there is filter return air grills there could be a filter in each one of those also there could be more than one central filter for system you know there could have been some accident where the building owner didn't realize that the filter was here and they started putting the one inside of the furnace or the air handler there could also be a filter rack cut into a duct and there may be one here and here and that was done by accident this is a very overlooked cause of low air flow and we are on the inside of an air handler cabinet the evaporator cooler right here has been removed but you see that this cabinet there's glue there that typically holds this insulation well a lot of times that let's go and then the the blower motor ends up sucking the insulation to the side of the squirrel cage and then it lowers the amount of airflow because the only sucking air and from this side so what happens is though when the blower motor shuts off this insulation a lot of times goes back up into position not in this case because it's horizontal but in a vertical system or a packaged unit or something like that a lot of times the insulation kind of moves back and you don't notice it so you got to kind of look around for a loose insulation on the inside of the cabinet of the system a dirty blower wheel will affect your air flow as well and the squirrel cage itself on the inside you want to make sure to clean that out as well you want to get that as smooth as possible you don't want to be completely rough so you want to get your brush and your shopback in there to clean that out another cost could be that the dip switches were never set properly to the correct air flow speed so this control board control would speed and ECM blur mutter we'll run it right here on this there's a pin connector that needs to be adjusted for the system size have you ever played find the supply registers before that's the game where you have to find where they're all at and then move all the furniture out from on top of them and sometimes are there under a couch or something like that and sometimes you have a cat or a dog laid on them you could have a return grill it's just too small or you may not have enough return grills and you may not have enough supply registers or they may not be the right size so that could be an issue another cause could be that the filter is just too restrictive so you could go with a less restrictive type such as this version right here or you could go with a pleated one that from the manufacturer it says that it has a lower pressure drop the other thing is you could go with a a wider pleated filter and that will be much better such as a three inch or a four inch one and that would have a much lower pressure drop across though this is a secondary heat exchanger for a 90% efficient furnace and that coil right there could get clogged up with dust and that would block the airflow it's possible that nobody ever checked the airflow to make sure that they had the proper airflow going across the coil and we've done several videos on that with a temporized formula with the total external static pressure and also with the hot wire anemometer so you can go ahead and check those out those are linked in the description section below another common issue is if this supply flex or multiple flexes are not installed onto the collar properly then they can just accidentally fall off over time maybe this is getting kicked in the attic and it gets pulled off or maybe this is in the crawlspace and there's no hanger and it just kind of falls off due to weight over time then you just have the air blowing out of the duct into the crawlspace and so in the building maybe you have one or two supply registers that don't have any air flow but all the rest do you're just pumping all of your air down into the crawlspace so you've got to make sure that the Flex is secured properly onto the collar you could have a clogged evaporator coil and it gets clogged with dust and that happens when you don't have a filter on a system and what's going to happen is you're just not going to have the air flow crossing this evaporator coil anymore so this would all need to get cleaned out of here you could have a frozen evaporator coil but that is usually due to one of three things either a low further in charge a liquid lamb restriction or to begin with he had low airflow but obviously now with a frozen coil you have no air flow check out the article that we wrote over in the website which differentiates between the low refrigerant charge low air flow and liquid lamb restriction we're looking into the inside of a rectangular duct with acoustical liner that's on the inner walls of the duct and if you have the glue and the buttons let go of the acoustical liners and the acoustical liner gets kind of sucked back in the return that could block the airflow so acoustical liner may have been used as insulation instead of on the outside of the duct but acoustical liners real uses to quiet the noise down in a short return duct another cause could be leaky joints in your ductwork so you want to make sure that they're sealed up well and even if you try to use tape a lot of times this duct this oily and the tape won't stick very well and a lot of times you see your insulation getting blown up like getting blown out when the system turns on and that means that you have leaky joints and you really want to seal those joints with duct mastic and you can get the duct mastic in a cork tube like this or in the tub and I have both of them linked down description section below another cause could be that the supply and the return trunk ducts were not sized for the size system that you have so for instance you have to take a look at the outdoor unit model number and look at the heat removal capacity in BTUs per hour and for every 12,000 BTUs per hour you're looking for roughly 400 CFM s of airflow and then you have to design your ductwork to accommodate that just because you can make a duct fit in an area doesn't mean it's a good idea so this is a 14 inch return flex with the insulation around it jammed into a six inch opening so it's definitely going to reduce the airflow another cost could be that you have too many 90-degree turns or too many dead ends and things like that in your duct so whenever possible always try to plan out for as many Street ducts as your for your trunks as possible because you got to remember that every time that you add a 90 degree turn in there it's not just the length of that turn itself that 90 degree turn the actual equivalent length of adding that into the duct is like adding a significant length of straight duct to your to your system another cost could be that the supply trunk bucked at the end of the law reduce too far in size and in this case we have a 12 inch duct it's actually 12 by 8 and you see that we have 1 2 3 4 5 supplies and literally two more behind me on this same size duct and this buck will not supply the correct amount of air volume needed for each of these supply runs another cost could be that an animal has made a nest in your return air flex and this could happen in a crawl space that's not sealed up such as a mobile home or if you leave the crawlspace door open and the next time that this system runs basically the return flex just collapses in and that's a lot of times what it would look like so you got to make sure that that crawlspace is all sealed up another reason could be a duct that's actually on a concrete floor and in that case there could be water that comes up and rots the duct I found before where a down flow furnace is pushing the air down into a into its plenum and then the bottom had rotted out and that's because where I live the water table comes up a little bit you know that could happen or you could have an evaporator coil up here that has a problem with condensate pan and it's dripping water into the bottom of the plenum and rotting it out blowing all the air out of the bottom of the plenum and not into the house so that's it that's the 20 causes a little airflow make sure to check out our website where we have plenty of resources there join us over on Facebook and follow us there and like our page we have quick tips happening every other day and so we've got a lot going on with our videos or articles and our quick tips make sure to check out a refrigerant charging and service procedures for air conditioning paperback workbook and quick cards which are all available over at amazon.com and we have all those products available over at our website as well including the e-book and we also have the e-book available over on google play make sure to subscribe and hit the bell notification in order to get an update anytime we post a new video hope you enjoyed yourself and we'll see you next time an easy service tech channel

Channel: AC Service Tech LLC

Views: 327,148

Keywords: acservicetech, repair, maintenance, how to, fix, hvac, hvacr, how do you, test, ac, service, tech, check, measure, read, superheat, subcooling, refrigerant, procedure, voltage, charging, temp, multimeter, freon, airflow, airflow problems, low airflow, mastic, ductwork, duct, air filter, filter, insulation

Id: T5eBsC_MZAI

Length: 8min 33sec (513 seconds)

Published: Sat May 02 2020