Vehicle AC System Diagnosis for Beginners. A/C System Troubleshooting

[Music] so today I'm going to show you guys how to diagnose an automotive AC system that does not cool um in the case of this Honda I have no cold air out of the dash so what we're going to do in this video is I'm going to take you guys through basically how to diagnose your system that does not cool what's involved with it specifically using a manifold gauge set now for those of you that aren't familiar with how automotive air conditioning works I'm just going to give you guys a very basic crash course as to what is actually going on in the automotive air conditioning system because if you have a basic understanding of what's actually going on here it'll make it much much easier for you guys to go about diagnosing the system so the automotive air conditioning system and pretty much the air conditioning system in your house and probably most refrigerators as far as I'm aware of all pretty much work off of the exact same principle that principle is called the latent heat of vaporization it is a fundamental principle of thermodynamics and I'm not going to get into a long drawn out discussion about thermodynamics because frankly it's irrelevant to diagnosing an AC system what you need to know about it is simply this if you were to take water and spray your arm with water what happens to the temperature of your arm that is wet when you blow some air across it your arm gets cold right do you know why your arm gets cold well the reason your arm gets cold is because the change in state from a liquid to a gas when the water evaporates pulls heat off of your arm and out into the atmosphere that is essentially what goes on in the automotive air conditioning system um in this example so when that water would evaporate the automotive air conditioning system contains that gas that is then condensed back into a liquid where it is then put back into the evaporator where it is then turned back into a gas again so it just circulates throughout the system changing from a liquid to a gas that is literally it and that change in state from a liquid to a gas removes heat from the evaporator so when you turn the blower motor on and blow air across it that air feels cold because the evaporator is cold that's it so now what we'll get into a little bit is we're going to take a look at some of the components in the system um how some of the components actually function and things like what the high pressure side is and what the low pressure side is and where is the liquid in the system versus where is the gas in the system um things like that because if you have a basic understanding of what's going on it's going to make this a piece of cake so taking a look at the diagram I have here on the screen guys um this diagram doesn't excellent job of showing you exactly what state the refrigerant is in in any given point in the system so what I'm going to do now is I'm going to sort of walk you guys through um each component and ultimately what that component is responsible for so you guys have a basic understanding of what's going on here so the first component we're going to talk about is going to be the compressor itself so the compressor's main job is it receives a low pressure gas and it discharges a high pressure gas the compressor is ultimately what's responsible for creating circulation of the refrigerant in the system um it also helps create pressure in the system the other thing that creates pressure in the system is the expansion valve which we'll talk about a little bit later but those two when it comes to system pressure um those two kind of work in conjunction with one another now as the refrigerant exits the compressor it's going to head to the condenser and the main job of the condenser is to take this high pressure gas that's discharged by the compressor condense it down into a high-press liquid um this is usually what's located in the front of the car and typically if you have a vehicle with a electric fan in the front of the car for the radiator and condenser when you turn the air conditioning on this is um the fan that turns on in the front of the car it's turning on to create this change in state from a gas into a high-press liquid now once the high press liquid exits the condenser the liquid goes through a dryer and the main job of this dryer is actually just to absorb any water that might occur in the system any sort of condensation or anything like that water in an AC system is bad news and it will cause the AC system to not cool um essentially what's inside this dryer is a large bag of desicant um if you guys have ever gotten any clothing or any furniture or anything like that it's basically the same thing just a much larger bag of that desicant that ultimately really is just what's in the dryer there's not a whole lot to the dryer itself um one of the issues you can have with a dryer is if that desant bag happens to come apart um it will clog up the system and it does a very good job of clogging up the system so once that high pressure liquid exits a dryer the next place it's going to go is going to be the expansion valve or the orice tube now depending on the style of system you have you either have an expansion valve or an orifice tube you do not have both what the job of these two devices are is what what it really does is it takes the high pressure liquid and turns it into a low pressure liquid now the main difference between an expansion valve in an orice tube is the expansion valve actually regulates the pressure in the evaporator an orice tube is simply just a really small hole that the refrigerant has to try and make its way through to get into the evaporator so kind of think of the um expansion valve or the TXV valve as sort of like a more intelligent if you will um air conditioning system than an orice tube because an orice tube is literally just a hole and the expansion valve is actually able to regulate pressure they have the F they have the exact same job um they just go about it two different ways so the final thing we're going to talk about here is going to be the evaporator and the evaporator does exactly what it says it takes the low press liquid and turns it into a low press gas so that this is literally the evaporator was what I was showing in the example on my arm you're taking that low pressure liquid evaporating it into a low pressure gas that low pressure gas goes right back into the compressor where it's recirculated and the whole cycle starts over again so essentially in a nutshell that's how the system works so now when you're attempting to diagnose the particular system that you're dealing with the absolute first thing that you need to check here is is the compressor actually engaging I'll be honest the compressor on this car is not engaging so I can do whatever I want on the dash you know demand as much cold air as I want if the compressor doesn't turn on as you guys just found out the refrigerant is never going to circulate around the system therefore you're never going to get any cold air so you have to get the compressor turned on so there's a few different things that could cause an AC clutch not to engage so first things first no refrigerant if there's no refrigerant in the system the clutch is never going to engage and the reason for that is the refrigerant itself that circulates throughout the system the refrigerant carries the oil throughout the system as well so the minute the refrigerant is all gone the oil is still in the system but it's not being circulated because the refrigerant is not there so in a case of a vehicle that has no refrigerant the compressor is never going to turn on because the compressor is never going to get any lubrication without the refrigerant in the case of this vehicle um what I did was the first place I went is I went right down to the AC clutch and I check for power and ground at the AC clutch um usually there's some sort of two-wire connector at the AC clutch magnetic coil that you can just unhook it check it for power and ground with a test light and that'll pretty and that'll pretty much tell you if the clutch is going to engage or not um the easiest way to do this is simply go inside the car turn on the air conditioning full blast unplug the clutch coil and check it for power and ground um in my case I did not have power and ground at the clutch coil what I ended up finding was the AC clutch relay in this car was bad once I got the AC clutch relay fixed and a new relay installed I then had power down at the clutch well not only was the AC relay bad the clutch in this car was also worn out at the same time so this is what you guys sort of have to keep in your mind as you're going about diagnosing your AC system just because you fixed one thing doesn't mean you don't have two more things wrong you know you might have three total things wrong and until you eliminate the first two you can't even find the third one this is a perfect example of that so yes the AC clutch relay was bad I got power down to my coil turned the car on went to engage the air conditioning guess what I also found out the AC clutch was bad so then I had to go through and replace the AC clutch in this car at this point yes the clutch is engaging this the compressor turns on but I still don't know if this car is going to cool or not based on the fact that you know what I may have something else wrong in addition to the two other things that I already fixed but you can't test those things until you get the compressor working so this is why when you guys go to a shop and they start quoting out AC work a lot of shops guys believe it or not will just start basically rebuilding the system I'll quote you a brand new compressor all new hoses brand new condenser the whole thing because they don't want to deal with this domino effect that I'm literally showing you on this on this video um they don't want to have to deal with the comeback you know 2 3 days later that the system is no longer operational after the customer just spent let's say $500 um replacing an AC clutch this is a perfect example of that so just be aware here guys that you know just because you fixed a couple things doesn't mean you don't have more things wrong now for those of you that are interested in um a video or some sort of tutorial on how to change out an AC clutch um I shot a video on that about 3 or 4 years ago at this point I will put a card in the corner and a link down in the description to that video if you need to do this uh AC clutch repair now with all that in mind really the next thing you need to do once you have the clutch working is get in the car fire it up again and see if you got cold air coming out of the dash um usually at this point if you've got cold air coming out of the dash generally speaking your system is usually good to go um if it's not and you still have issues with no cold air coming out of the dash and the compressor is running now we're going to start getting into um reading the manifold gauge pressures and you're going to be able to correlate these manifold gauge pressures um with different system problems now for those of you that aren't familiar this is a manifold gauge set and this is what we're going to use to diagnose what is actually going on with the system so the red side over here is the high pressure side the blue is the low pressure side and if you take a look at the connections that clip onto the uh the ports in the system the red is much bigger than the blue low pressure side so it's pretty much impossible to get these two backwards um this is where that they would connect to the system and if you take a look you can see you know there's totally a difference in size between the high pressure port and the low pressure port so it's pretty much impossible to get these things mixed up um now before you connect it to the system what you need to do is you actually need to pull a vacuum on the hoses on the manifold gauge set and to do this you're going to be using a vacuum pump the reason you need to do this is because these hoses have air in them you do not want to introduce any sort of air into the refrigerant and the AC system because the air as you would imagine will not cool so the yellow hose in the middle goes to the vacuum pump and connects to the vacuum pump down here then what you're going to do you're going to turn the vacuum pump on and then you're going to open both valves what these two valves do is they simply connect the red hose to the yellow line if you open this valve or the blue hose to the yellow line if you open this valve that's it so without anything connected you're going to pull a vacuum on this [Music] system so now I'm going to come up here now the uh vacum pump's running going to suck down the high side suck down the low side and you can see on the low side on this gauge set it did go into vacuum so I'm going to give this probably 5 minutes or so just make sure there's no contaminants in the two lines that you're going to connect to the system and then we're just going to go ahead and attach the the blue and the red hose here and here so I got both my valves closed here you can see my vacuum is holding on my gauge set so now I'm pretty much ready to start connecting to the system now to do this the uh the manifold gauge set I have just push locks onto the connectors so if you watch when I connect this there you go that's my static system pressure that I'm reading right now let me uh connect up my high side and there you go if you look um those pressure readings should be about equal on both both gauges now I'll be honest with you guys there's a bunch of people out there that'll diagnose the system based on the static pressure readings um I'm here to tell you the static pressure readings really don't tell you a whole heck of a lot um they simply just tell you whether or not the system has refrigerant in it or not if the system doesn't have refrigerant like I alluded to a minute ago you'll never get the the uh clutch to engage so if you're if you're having AC clutch problems double check and make sure you have refrigerant first so the next thing I got to do simply start the car up and I'm going to turn on air conditioning full blast Max AC and go out and take a look at my pressure eatings so it's still starting to stabilize you can see my high pressure is coming up or my high Sid's coming up to that's probably 160 climbing probably 175 is 170ish low side is about 30 or so um at this point now I'm going to go over in detail what pressures you need to be checking here what these pressures should be from low side to high and high side to low as well as in your ambient conditions it's also going to change what these pressures should be so let's dive into that now so now that you have the manifold gauge set all hooked up to the vehicle um the next thing you need to do is you need to just take a minute and do a Google search on a temperature pressure chart you need to Google a temperature pressure chart for the type of refrigerant you're dealing with so for example I'm dealing with R134a on this 08 Civic I need to Google a temperature pressure chart for R134a and what that's going to do for you is a couple things so refrigerant in the system changes pressure based on the ambient temperature that you're dealing with and what these charts tell you is let's say at 50° outside what the pressure on the high and low side should be and then at 90° they will also tell you what the pressure in the high and low side should be so based on your current ambient temperature it's going to change what these pressure readings are that you're seeing and when you start diagnosing a system you really need to know what the pressure quote unquote sort of should be before you start making assumptions and trying to to diagnose a system that does not cool you need to know where it needs to be to know if what you have is wrong that's what I'm getting at here so what I'm going to do for you guys is kind of take you through scenario by scenario um based on what you're seeing with these pressure readings that's going to give you some insight to what's actually going on with your system and it's going to give you Clues on where to look for problems so the first situation we're going to talk about is where your high and low side pressures are largely where they should be but the system still isn't blowing any cold air out of the dash in that scenario if the pressures are where they should be but you have no cold air coming out of the dash your issue is not with the air conditioning system um your issue is with something inside the dash that could be um the heater control you know where you select from hot to cold it could be an issue with the blower motor it could be um with an issue with the blend door that actually moves inside the dash to select hot and cold your system is functioning properly if the pressures are where they should be you have a issue somewhere else related to not being able to get the cold air out of the dashboard that's where you need to go so this next scenario that we're going to talk about is probably the most common scenario that you're going to find and that is going to be a low low side pressure and a low high side pressure in this scenario there's a couple different things that can cause this first of all again it could be the ambient temperature that you're taking these readings in is very very low causing the pressure in the system to be very low the other thing that can cause this is a low refrigerant charge if there isn't enough refrigerant in the system the system can't build pressure correctly and that's what you're seeing um that's most characterized by a low low side and a low high side is pretty indicative of the fact that you know what the system needs more refrigerant so this next scenario that we're going to talk about is going to be just the opposite of what we dealt with a second ago this is going to be a high low side pressure and a high high side pressure this again could be related to the ambient conditions that you're dealing with if it's extremely hot outside your pressures in the that you see in the system are going to be much much hotter than what they would be on a colder day so take that into account when you're looking at all these readings the other thing that it could tell you is it could tell you that the system is in fact overcharged if there's too much refrigerant in the system it will cause your low side pressure to be too high it will also cause your high side pressure to be too high now a couple of the things that will cause a high low side pressure and a high high side pressure could be air in the system if air is introduced into the refrigerant it does not cool correctly and it causes issues with the pressure that you would see where both the high and low side pressures are too high in addition to that the other thing you need to take a look at is going to be the AC condenser if the AC condenser in the front of the car has been damaged it's plugged or let's say it has no airf flow because the fans AR are inoperable um that is again is going to cause a high low side pressure and a high high side pressure um those are kind of all the basic things that you should be looking at in that scenario so the next scenario we're going to talk about here is going to be a situation where the low side pressure is too high and the high side pressure is too low in that scenario you really need to check the compressor if the compressor first of all doesn't turn on you're never going to get that separation and pressure like you should where the high side comes up and the low side goes down that usually indicates a compressor issue in some way shape or form now there are exceptions to the rule that I'm going to go over in a second but with that said if the compressor is worn out what you'll see is the instead of the high side coming up to where it's supposed to be and the low side coming down where it's supposed to be they'll run very close to one another because that compressor is so worn out that it can't produce the pressure that it should be same thing with like a slipping clutch or a clutch that doesn't engage as you guys saw in my scenario my clutch wasn't engaging when I started out working on this car so if the clutch doesn't engage you're never going to get that separation and pressure like you should the other thing that can cause a um high side pressure to be too low and a low side pressure to be too high would be the metering device so that could be the thermal expansion valve being stuck open or like an orifice tube that has a hole in it or isn't installed in that scenario um where the metering device um may have an issue typically what happens is when you turn the air conditioner off the the pressures will even out very very quickly because there's no restriction in the system the orice tube and the thermal expansion valve ultimately are what create that separation and pressure in the system and if one of those things is screwed up like if you have a hole in the orice tube that's too big or you have a expansion valve that's stuck open it's going to flow too much refrigerant if it's flowing too much refrigerant the pressures are going to be largely equal and when you turn the air conditioner off they're going to go back to that static pressure very very quickly because there's no restriction in the system to keep the pressure separated now the final scenario that I'm going to talk about in this video is going to be a low side pressure that is too low and a high side pressure that is too high in that scenario um You probably have some sort of contamination in the system so if you have water in the system it's going to cause this sort of issue the other thing that causes this issue could be too much oil in the in the system and I'm going to talk about this for a second so if you guys have a system that has a slow leak and you've been putting stop leak in it over and over and over again the when the refrigerant leaks leaks out it's going to leave behind that stop leak so if you keep charging your system multiple times with a product with stop leak in it you've now completely oversaturated your system with oil and your system is never going to cool correctly even though you're putting refrigerant in it so this is one of the reasons why I'm not personally a huge fan of stop leak because I think stop leak is one of those things that gets abused a little bit too much if you want to put one can in it sure if doesn't fix your issue two more cans aren't going to fix it either so I'm a big advocate of just using Straight gas in the system because of what I just told you if you oversaturate the system with oil it's going to cause cooling problems the only way that you can get that oil out of the system is you have to take the whole system apart flush everything out and completely recharge it I actually have a video on how to do this I'll put a card up in the corner Link in the description to that video now the other way that you would have a low pressure side too low and a high pressure side too high would be again an issue with the metering device if you have contamination caught in the orice tube like let's say your compressor is starting to go out and all the contaminants from the compressor are starting to plug up the orice tube it's not going to let the refrigerant flow through the system as it should and it's going to cause that huge differential and pressure between the high side and the low side again a thermal expansion valve that's stuck closed it is going to cause a similar issue as a plugged orice tube it's not going to let that refrigerant flow through the system like it should be it's not going to cool correctly and you're going to have a huge disparity between your high pressure and low pressure because once the refrigerant goes out of the compressor it has nowhere to go because the system's plugged so guys that's pretty much what I have for this video if you guys have any other questions as far as diagnosing your system put it down in the comments I'll do as best I can to try and get back with you guys um if what you're asking isn't already in the video somewhere um guys I will also have links to the manifold gauge set and the vacuum pump in one kit if you guys are interested in that for about 125 bucks seems like a pretty decent deal when you uh start shopping around a little bit and if you buy that kit you have pretty much everything that you need to be able to do AC work on your own other than obviously recover the refrigerant as always guys if you guys like the video hit like if you want to see more content go down hit subscribe thanks for watching guys [Music]

Channel: Repair Geek

Views: 33,563

Keywords: ac system recharge, ac blows warm air, air conditioning, diagnosis, not working, blows warm air, ac not working, ac diagnosis, car blows hot air, automotive, ac, gauges, manifold gauge, manifold gauge reading, ac clutch not working, ac clutch, ac doesn't work, a/c, ac clutch test, ac repair, ac stop leak, ac not blowing cold, ac blows hot, r134a, 1234yf, ac pressure diagnosis, ac recharge, ac troubleshooting, car ac diagnosis, troubleshooting, repair, diy ac repair

Id: QAJv4U1JeRA

Length: 25min 20sec (1520 seconds)

Published: Sat May 25 2024