Automotive AC Diagnostics, Operation and Repair

hey how's it going dude sulfurs got an awesome one for you today today i'm going to show you how you can diagnose problems and issues with your car's ac system using an el cheapo ac manifold gauge set we'll also go over the different pressure readings you might get on the low side and the high side of your ac system and how you can use those readings to diagnose issues with your car but not just that we'll also talk about the electrical side of your ac system like your ac pressure switches and your ac compressor clutch coil as well and the ac system we're going to try to fix today is going to be on this 1997 mercury mountaineer but you should be able to use the diagnostic procedures in this video to work on any car you make and model all right before anybody else says it you guys like my hood prop so a little background on this car before we get started the owner tells me that the ac system on this vehicle stopped working about two or three years ago but since it had only about a billion miles on it that is high enough to get it diagnosed or fixed all right so i guess that wasn't much of a back story but anyway let's get started all right so on a car like this first thing i want to do is to do a quick visual inspection i'm going to take a look at the compressor clutch and pulley make sure they're not physically damaged take a look at our ac lines make sure they're in good physical shape especially where they connect to the condenser of course take a very close look and inspect the condenser as well all right so all that checks out on this car next i'm going to see whether there's any refrigerant on our a system at all go and do it like a rat neck whoa yeah it's got a refrigerant all right so that was surprising i didn't expect this thing to have any refrigerant actually but anyway next we have no choice but to whip out and play with our toy and by that i mean our ac manifold gauge set and by the way if you're interested in this tool or any other tools or products i end up using in this video and you want to buy them online i'll put links to where you can buy them for cheap down below in the description box so don't be afraid to click on them and check them out now for those of you that are not familiar with these let me explain to you how they work so on an ac manifold gauge set you'll have two sets of gauges you'll have a red one for your high pressure side and the numbers you want to use are going to be these psi numbers inside this small circle here and then you have a blue one for the low pressure side and again you want to use the psi numbers inside here and then you have these quick connect couplers that will attach to the service ports on your asus system and you got the red one again for the high pressure side and the blue one for the low pressure side now for reading pressures inside your ac system these are all you need to pay attention to but you have also these valves that open up your high pressure side and low pressure side to this yellow line now when you open these you only open them when you're about to evacuate the system or vacuum the system or add refrigerant all through this yellow line so under normal circumstances both these valves well there's one blue valve here there's supposed to be a red one here but again this is an el cheapo manifold but it still works but anyway these two valves need to be closed so that refrigerant doesn't go from your ac system into this yellow line when you're only checking for pressure all right so next we'll grab one of our quick connect couplers and make sure that this valve inside here is out all the way by turning this counterclockwise all right so next you'll grab your qriket coupler pull back on this install it on your service port push down let go make sure it's firmly attached and that's it and you can't really connect these to the wrong one because the high pressure service port has a larger diameter than the low pressure side so these are pretty dummy proof next after you install them you want to start running down your valve and as soon as our shredder valve opens and if we have any refrigerant in the system we should get a reading as you can see we've got about an 80 psi or so of pressure on our high pressure side all right so next we'll do the same thing on our low pressure set and you should have more or less the same pressure on the low pressure side with your engine off and ac compressor clutch not engaged obviously as you can see we got about the exact amount of pressure on both sides we got 80 psi here and 80 psi here as well and that's called your static pressure and that's exactly what you want to see you want to see the same pressure on both sides when the compressor is not working now as far as why that is well let's go over quickly of how an ac system works on your car we will start at your ac compressor alright so normally when you do not have your ac on your ac compressor or rather the pulley here is basically just freewheeling and turning with your drive shaft but when you turn on your ac and if you have enough refrigerant in the system your car's hvac module will engage your ac compressor clutch so right there in front of the pulley that's your ac compressor clutch and here's a connector for ac compressor clutch coil that when activated engages your ac compressor clutch and when the clutch is engaged your c compressor starts working and it takes refrigerant from the low side compresses it and sends it to where your high side starts at your ac condenser then from your ac condenser depending on your setup refrigerant goes to either an orifice tube or an expansion valve on this car here we have an orifice tube which basically both of their job is to force the compressed refrigerant through a very small opening or orifice and when that happens and as the refrigerant expands from there it will go to a low pressure side and expands quickly and therefore cool down rapidly and when that happens it goes to your evaporator which is usually in some god forsaken place inside your dash and also that's where your blower fan is your blower fan blows the warm air over your evaporator your evaporator absorbs the the heat from that air therefore cooling it down and that's how you get that nice cool air inside your cabin when you do have a working ac system and from there if your ac system has an orifice tube the refrigerant goes to what's called an accumulator which is this guy right here now the job of your accumulator is to filter the refrigerant and make sure there is no debris or any moisture in the refrigerant but more importantly is to capture any refrigerant that's in the liquid form so it doesn't pass on from here into your compressor because if that happens the liquid refrigerant can damage your ac compressor so when the ac compressor is working you're going to have a lot of pressure on your high pressure side which is in red here and when it passes your orifice tube or expansion valve it goes to the low pressure side which is in blue here and the reason why you want to see equal numbers when the compressor is not engaged is obviously when the compressor is not engaged refrigerant starts leaking back from the high pressure side into the low pressure side and being equal on both sides and that's if you have a working ac system or let's say if you have a clogged orifice tube it's not going to allow for the refrigerant to pass from the high pressure side into the low pressure side and therefore you're going to have different numbers for the for each side all right so next we're going to get our car start our engine and turn on our ac and see whether our ac compressor clutch engages or not now since we have enough pressure in our low side our ac compressor clutch should engage if the electrical circuit is working properly and if you're wondering pretty much anything past 25 or 30 psi on the low side should allow for your ac compressor clutch to engage i'll explain why that is in a little while but for now let's turn on our ac so we'll put this on max make sure this is in the cold position all right that feels a little funny make sure this is on max as well so here you guys can actually see the clutch engage and disengage on this ac compressor all right so here's our pressure readings now when the compressor clutch engages like right now you can see the needle on this side goes to about 140 135 and you want to take your release when the compressor clutch engages by the way and then you're engaged again and on the low pressure side it's at about 30 30 and maybe 32 or 3. and on the low pressure side you can see that right there you headed the clutch engages right when this hits 35 psi and as it goes down it disengages when it goes below 30 psi all right now that we have these numbers what do they mean and how can we use them to diagnose issues with our ac system now these numbers are going to be a little different from car to car you know every system has its own numbers for different uh temperatures and humidity when you do that test but from experience i can tell you that these numbers are actually okay uh they pretty much indicate that it might be a slightly low on refrigerant and that's why the compressor clutch keeps engaging and disengaging all right so the way your ac compressor knows when to turn on and turn off is through your low side ac pressure switch or compressor cycling switch which again is on the low side this two-wire switch that you see here on our accumulator so basically this switch is usually in the open position in other words when it's open it doesn't let the current to pass through it but when you have enough pressure inside your low pressure side it pushes up against the switch and it closes the connection inside the switch and allows for current to pass through and when current pass through that it goes from there usually to your ac compressor clutch which is already grounded and when it gets that current from your ac a low pressure side switch it turns on and starts pumping the refrigerant from the low side into the high pressure side but then again as it comes to the refrigerant from the low side to the high pressure side the pressure inside your low side goes down below a certain threshold and when it goes down below certain threshold your low pressure side switch opens and when it opens it cuts the current to your compressor and that's why it disengages and then the whole cycle repeats itself and then when you have low refrigerant this just happens more and more quickly now for whatever reason you don't have access to the repair manual for your car you can use these numbers you see here to give you a general guide so for example right now over here is about a 75 degrees fahrenheit above 60 humidity so on the low side we should have 27 to 42 psi of pressure and on the high side we should have 128 281 psi of pressure and i know that's a bit of a wide range but you can see we have here we have about 30 or maybe 31 or 32 on the low side and then we have 140 and for both for both sides we're on the lower side so we can conclude that we are just a little low on refrigerant and this car's ac system all right so now let's talk about if you get different numbers than the ones we got here so now let's say we have the same number or the same pressure on both sides even when the ac compressor clutch is engaged if that's the case let's say you're getting 80 psi on both sides with the compressor clutch engaged and the engine running basically means you have a shot ac compressor it's basically not compressing the refrigerant that's coming to it from the low side or perhaps maybe there are chick valves here that keep refrigerant from this side going out and not back in and from this side coming in and not back out whatever the main case may be you have a bad ac compressor and you need to replace it or rebuild it all right so next let's say you have higher pressure on the high side than what you're supposed to have and then lower than what you're supposed to have pressure on the low side now if that's the case and if it's bad enough your ac compressor clutch might not even engage because the pressure on the low side is going to be so low where the low side pressure switch is not going to close and allow current to flow to your ac compressor clutch but basically it means that you're going to have a clog in your high pressure side and the main culprit on a setup like this is going to be your orifice tube okay so another scenario would be when you have lower than expected pressure on the high side and then higher than expected pressure on the low side now this is going to be more common with setups that have an expansion valve instead of an orifice tube but basically would mean that the expansion valve is stuck in the open position and this compressed refrigerant on this side can easily get into the low pressure side raising the pressure on that side and lowering the pressure on the high pressure side it also could mean that you could potentially have a check valve inside your ac compressor on the low side that's uh stuck closed and doesn't let the refrigerant to get inside the compressor easily but generally speaking you get these numbers when you have an expansion valve and it's stuck open all right so there's that but as far as what's wrong with this car besides the low refrigerant well you're probably not gonna believe it the problem is this guy right here see this is completely shot and it's not working and i believe that this is actually broken in the all the way in the hot position because with the engine running and the ac off and even though this knob i'm gonna put it here on the cool side the air coming out of these air vents is super hot so that's why they don't feel the cool air coming out of this even though their ac system is kind of working it's a little low on refrigerant but it should still cool the air coming out of these air vents so in other words for the last three years in the southern california heat the ac system works fine it's just that knob that hasn't been working right hold it i spoke way too soon so this thing being a 97 mercury i imagine this controlled for the temperature would be either mechanically controlled by cable or by vacuum but as you can see this is actually controlled by a potentiometer here so basically the way this works is that when you turn the key on there's current available at the potentiometer or your temperature control knob as you turn that temperature control either to the right or to the left the resistance in that potentiometer changes and as a result the current flowing through it and out of it changes as well and that changing current from there goes to your blend door actuator on your heater core assembly and it either opens or closes that blend door which as a result allows for either air from your heater core or from your evaporator to flow through your vent system and then out of your air vents all right so next with key on engine off i'm going to use my test light to see whether we have current at any of these pins here and as you can see we do have currents on this wire all the way to the right next you want to go and attach your test light to the positive side of your battery and then check for a ground at this connector as you can see on the one on the way to the left we have ground all right so basically current comes through the wire on the right through this potentiometer and as you turn the knob the resistance inside there changes and the signal voltage or current goes through the center wire back to our blend door actuator so here i've attached my test leads to those two wires on the right and the middle and as you can see we got about 5000 ohms of resistance right now so if this potentiometer is working correctly as i turn this knob for our temperature control the resistance we see here should change and as you can see indeed it does so this potentiometer is not our problem so down the rabbit hole we go next up to our blender actuator this guy right here this thing sits on top of this plenum like this and this piece here opens and closes the blend door in there which allows for either hot air or cooler or colder to flow through our vent system so again if this is working correctly as we turn that the temperature knob this thing should move as well and as you can see it does move as we turn that temperature knob all right so unfortunately it seems that actually the problem is the actual blend door as in the mechanical blend door inside of that plenum itself and from the research i can find online it seems to be a common problem where it breaks and then the hot air and the colder combine and come out of your air vents together and unfortunately the cure for that is that you have to replace that entire housing with the blend door inside of it you can't just replace the blend door and in order to replace that housing you have to remove it from the inside of your dash and i'm sure it's a pretty big job i haven't even looked at the labor hours for that but i have to talk to the owner and see whether he wants to do that or not i have a good feeling that he's not going to bother with it all right i know everybody was waiting for a more fulfilling outcome but you know as that one philosopher once said you can't always get what you want but if you try sometimes you can make lemonade with it or something like that but anyway hope you enjoyed this video if you did do me a favor and share this video on your favorite social network and also click on these other related videos of which i put links to on this side of the screen there will also be links down below in the description box as well all right thanks for watching i'll see you guys [Music] you

Channel: Ratchets And Wrenches

Views: 1,067,772

Keywords: Rathcets and Wrenches, how fix and ac system, how to add refrigerant to an ac system, r134a, r12, how to use an ac manifold guage set, how to add freon to a car ac system, how to get cold ac, AC blows warm air, how to fix an ac that's not cold, ac system recharge, how to service a car's ac system, how to repair a car ac, how to diagnose issues with pressure reading, high side, low side, high, low, psi, orifice tube, accumulator, expansion valve, evaporator, condensor, ac compressor

Id: BXTZURC5iQ0

Length: 16min 47sec (1007 seconds)

Published: Mon Jun 12 2017