A/C basics...Using manifold gauges to determine a/c problems in a semi truck | a/c pressure readings

hey guys welcome back to the channel today we're gonna talk about the basics of using an air conditioning set of manifold gauges to diagnose some different problems with your air conditioning this is kind of a follow up to the video of why your fan won't turn off we talked about if you have high pressure in your system in your air conditioning system they can cause that so I'm going to show you how to look for that today I talked about some different pressures and what they mean if you like this kind of thing make sure you hit that like button and subscribe share it with a friend been looking at my analytics and it shows that only about 20% of you that watch my videos are subscribed it means about 80% of you people that watch my videos are not subscribed so I'd really appreciate it if you could do that for me you can get a set of very affordable manifold gauges at Harbor Freight for about $60 and learning how to use them as priceless now before we start it's important to know whatever you're working with air conditioning I always wear some safety glasses or eye protection because you're dealing with pressurized r134 if you spray yourself in the eyes you can get harmed really bad so just know that now we're gonna do most of this video with the truck off you're just talking about different things because once I turn this thing on it's gonna get loud and you may not be able to hear me so I may have to voice over that part this is by no means a complete air conditioning diagnostic video I'll have a few more to come talking about some different problems this is just gonna be some basic information on how to use these things and you can do for their homework from there or we can discuss it further now the first thing we want to do there's a debate over static pressure and dynamic pressure static pressure is with the truck off you can get some readings they're not all that valid better readings come from when a truck is running but there's one static pressure that I want to get and this truck has been sitting it's at ambient air temperature which is probably in the high 70s I don't know exact temperature right now so we want to make sure that our high pressure side and our low pressure side are equalized at ambient air to air temperature and kind of what that's going to tell us a little bit is that after the truck was shut off the pressures were able to equalize indicating there's no obstruction inside the line so we're gonna we're gonna do that here quick now the red here cuz you got to put these hoses together they come inside a kit you want you want to start with all these valves closed all four valves make double sure that they are closed okay now that one's up here turn the natural way the ones on this end they turn the opposite way you would think so make sure you follow the directions on there close this counterclockwise the opposite of what you're used to and up here closed is the normal way this is important because if these valves are open when you try to put them on your on your valves there you're gonna shoot some refrigerant out right at your face we don't want that so you gotta locate your your two valves here well first you'll notice there are two different sizes so you can't screw this up the high pressure side is bigger than the low pressure side it's gonna be the same on here so locate your valves every truck they may be in different spots some might be up towards the firewall more take these caps off don't lose the caps you want them on there for dust protection all right okay Red's gonna go on the big one you just pull this collar back push it down on there it'll snap on so that's on there okay and then same thing with the low-pressure side the blue okay we're on there good now I'm gonna open these valves and we're gonna get some pressure here and we want to ok first before we do that a good set of gauges a nice set of gauges will come with a temperature correlation chart or you can download a temperature correlation chart off the internet it's right here probably can't see that I can barely see it it says Fahrenheit so out here we got the temperature it'll show you now pressures depend on ambient air temperature and somewhat humidity so it shows at 80 degrees ambient air temperature we should be at about 90 pounds something like that I can't read that real well without my glasses so the important part is that these two are equal it's not so important what the pressure is right now at this point it will be later when we start the truck up so I'm going to open these two valves up this open them slow and you can watch your gauges here there okay we open the low one jumped right up there opening up the high one okay you'll see that jump up too so on the low side worried about 86 pounds or so on the high side I'd say we're right about there so we're pretty even they said it's at this point it's not that important what the numbers are it's important that they're equal they're equalized when we're done with this and we shut the truck back off we're gonna watch these gauges and see that they equalize again it could take 10 minutes it could take an hour but the important part is to equalize it in at a steady rate okay that shows that there's not really an obstruction in there it's able to function properly before we start the truck up well eventually here what we're gonna do is start the truck up put it on high idle and crank the air conditioning wide open then we're gonna let the truck warm up and then we're gonna look at our pressures okay what's going to happen when the compressor kicks in this high pressure is going to go up the low pressure is going to go down when the compressor kicks out the high-pressure is gonna go down and the low pressure is gonna recover a little bit so kind of what I'm looking for I just got a range here of what I'm looking for with this truck is on the high side when the compressor is running 150 to 300 now at 300 the engine fan should kick in when engine fan kicks in it's gonna start bringing that pressure down some that's what the engine fans job is that's why when you're reading high pressure or I'm sorry if your engine fan is on because you're reading high pressure and because you have a faulty air conditioning high pressure switch that switch just reads you have high pressure all the time whether you do or not if it's bad so with the fan on it's trying to bring that pressure down and if the switch doesn't recognize that the pressure is coming down that the fan will just keep trying it'll stay running so when this when pressure creeps up the engine fan kicks in it'll drop that pressure down when it drops down so far the engine fan will kick back out okay and the low-pressure side should kind of move kind of like in Reverse of the high pressure side now the compressor will kick in and out based on what it needs if the compressor is what we call short cycling which is on off on off on off we don't want that that's a sign of low charge in the refrigerant okay this truck is functioning the way it should so I'm not going to evacuate the system or do anything here we're just wanting to read the gauges to see how everything that it's working properly and I'm going with that range of pressure because like I said - it can depend on ambient air temperature humidity and stuff like that but that's kind of the range I want it to be in you can look on a correlation chart too to see what what your should be at and they're all going to honestly they're all going to run slightly different and for the low side I'm looking for like 30 to 50 pounds is where I expect that will be I've repaired this air-conditioning a couple times when I've had leaks put a new compressor on so I kind of know the range that it runs in now let's just discuss well it's quiet here before it gets loud some different pressures and what they could mean if you're reading low pressure on the low side and low pressure on the high side but they're equal say they're both reading 20 pounds that's a sign that your compressor could be bad and it's not running and make and building pressure if you're running low pressure on both sides but there's a difference in the pressures say your low side is at 10 psi and your high side is at 60 they're both low but they're not equal then that indicates a low charge in the system you could be low on refrigerant so also to go along with that if you're reading high on both sides and they're in their equal that also could be a compressor issue if they're if the pressures are equal but if you're riding high on both sides but the pressures are not equal say the low sides running it at 90 well that's too high on the low side in this high side Peg's out at 300 and it doesn't come down well that's high on both sides but they're not equal that means you got probably too much refriger in the system it's overcharging if you're running high pressure on the low side and low pressure on the high side you could have an expansion valve that's stuck open and because it's stuck open it's not letting it build pressure on the high side so that would be an indication of high pressure over here and low pressure on the high side now if you have a reverse of that situation and you have low pressure on the low side and the high side is pressure is running high and it stays kind of high then that would be an indication of a blockage somewhere and typically blockages happen a lot of times in the expansion valve again although I can be you could have a pinch line you collapsed hose your receiver dryer could be obstructed you could have something wrong with the condenser if you've ever had a compressor shell out on you you're going to put some metal into the lines and that metal could build up somewhere and cause a blockage or get stuck in your expansion valve and and kind of block it so expansion valve needs to open and close and it wouldn't be able to do that hey once again I don't know if I said it or not but high pressure on both sides unequal can be an overcharge in the system so I think I'm ready to start this truck up we're not gonna let it run for very long all I want to show you is that how okay so besides the pressure mainly what I'm looking at is movement of the needles I don't want them stuttering like this on either side and if you have a stutter like that sometimes that could be like a bad valve in the compressor so we don't want that and I also want to see I don't know what the term for it is but I call it recovery time like when the compressor kicks out and the high pressure drops and the low pressure starts to rise I want to see that they kind of happen at the same time like they're supposed to like there's no lag time or delay that just indicates things are flowing in there like they're supposed to so you're gonna see my engine fan is gonna start up right away I just got done washing my radiator so there's gonna blow some water out make a mess a little bit but I gotta warm this truck up before we can take readings you're gonna see the high pressure rise but then you're gonna see it drop and it's gonna stay low but it's going to if the engine fan is running it's gonna it's gonna come down so we want to kind of read it with the fan on and fan off and and just make sure that it's it's rising and falling like it's supposed to and then the low side will do what it does so I'm gonna start this thing up and warm it up and we'll we'll just take a look and I'll probably have to block out the sound it's gonna be really loud right now you can see the compressors off let's watch this think okay the compressor just kicked in you can see the high pressure rising a little bit it's above 150 the low side is dropped the engine fan is off right now so let's just give it a second here okay the compressor just kicked out you can see the high pressure dropping and the low pressure pressure is climbing some we'll kick back in here shortly alright I see what's happening here I don't like my pressure is not going quite as high as I want it to and the low pressure is also a little low let's just watch it here a little bit see what happens and you can tell by how that's cycling that compressor is kicking on and off and it's short cycling that's called short cycling so I'm a little bit low on on charge here air conditioning is however blowing nice and cold but it's good to know this because I should suck the system down and recharge it I mean we are within technically within spec being over 150 pounds but I like to see it a little bit higher than that and the low-pressure side is is lower than I'd like it to be okay so I just shut the truck off and we want to watch that these pressures equalize they're gonna go very slow this could take ten minutes it could take an hour but the important part is that they do equalize you can see the low-pressure is creeping up slightly very slowly and the high pressure is falling very slowly you probably falling a little too slowly for you to notice but I can see it standing here so I'm just going to keep an eye on it last time I checked it it took about 15 minutes for it to equalize which is really good equalizing means we don't likely have an obstruction so we can go ahead and take this apart here you want to close your valves make sure they're close nice and snug [Music] came apart just like we put them on make sure you put these caps back on so you don't lose them okay so what we saw here is is it functioned the way it was supposed to however I feel like my pressures were a little bit lower than I wanted just a little bit and my compressor was short cycling which indicates between the the pressures being slightly low and the compressor short cycling would indicate to me I have a low charge in in my refrigerant my r134 so but it's still blowing pretty cold for now and then all the time so maybe next weekend when I get to it we are going to recharge this thing and I'll I'll try and show you out I'll try and show you how to do that so we're all done with this for today so understanding these different pressures what they do and what they mean can go a long ways towards trying to figure out what's wrong with your air conditioning and hopefully save you a fair bit of diagnostic time if you decide to take it into the shop you'll know just what's wrong before you take it in there now one thing I do always when I charge the system I always put dye in it no matter what because if you have a leak somewhere it's easy to find would die I can find it without the light or the glasses for finding UV leaks you'll just see green coming out check all your fittings and and and stuff your condenser even check in these valves here these things can leak there it's just a little valve stem in there you can replace it that way if you do go into a shop for repair you can save a lot of diagnostic time you can see the leak is right there because they'll otherwise dink around and evacuate the system put some dye in it and then try and find the leak if you already know what it is you can save yourself a lot of money in diagnostic time so I hope this video helped you out a lot and we'll see you next time

Channel: DIY SEMI

Views: 137,900

Keywords: Diy, Freightliner, truck repair, maintenance, truck maintenance, semi truck, semi, 18 wheeler, cdl, peterbilt, kenworth, westetn star, volvo, mack, international, drive shaft, hvac, blower motor, air bag, Air brakes, tires, air conditioning, turbo, diy semi, shocks, water pump, detroit diesel, Cummins, cat, series 60, isx, glider kit, air dryer, solenoid, Sleeper, Charge air cooler, radiator, A/c, Manifold gauges, Air conditioning

Id: vnIbKQNGHcI

Length: 18min 11sec (1091 seconds)

Published: Sat Jul 18 2020