How to Diagnose and Recharge Your AC System with Refrigerant – Using an A/C Manifold Gauge Set

How to Diagnose and Recharge Your AC System with Refrigerant – Using an A/C Manifold Gauge Set

Hey how is it going do it yourselfers, today
I am going to show you how you can use an A/C manifold gauge set to diagnose problems
with your cars AC system, but not just that I will also go over how you can use it to
add refrigerant to your ac system as well. Alright so on the left side we got this in
blue this is going to be for the low pressure side, and this gauge on the right side is
going to be for our high pressure side. And than we got these two connectors at the end
that will attach to the pressure ports on our high and low pressure lines of our ac
system and thats how we’ll get the pressure readings on these gauges. And these guys are
just attached to the manifolds at the ends here, and these don’t do anything they are
just there so that you can attach these to them, they have no practical purpose besides
that. And the way these guys work is that there is a quick connect coupler at the end
of them which you pull out and than you would put this over the pressure port so this one
is going to be the low side pressure port and than once you let it go it holds it in
place and than you run down this valve, this valve here would press down on a schrader
valve that’s on your connector for the low side and open up the system to your ac manifold
gauges. Alright next let me explain to you what these two knobs here do or actually in
this case this one knob, there is another knob thats supposed to be here just in red
but it’s broken on mine and its missing but just imagine there is another knob like this
here that’s red. Once you open these, these will open up your low and high pressure sides
to center line, this yellow line. And this center line is used to add either refrigerant
to your system, or completely evacuate the system of refrigerant or pull a vacuum on
a system after a repair to confirm that there are no leaks in the system. Now as far as
where you attach your connectors it’s pretty, if you are lucky enough you’ll have a plastic
cap like this that says H on it. And once you unscrew that you’ll see the pressure port
where you would connect your high pressure side, but if you are not lucky enough to have
those plastic caps fear non the connector that goes to the high pressure side is going
to be the diameter on the inside of it is going to be larger than the one that goes
on the low pressure side. In so many words these are basically dummy proof and you really
can’t put them on wrong. Alright so I going to go ahead and attach this to our high pressure
side, after I attach it you just want to pull on it slightly make sure it’s secured in place.
And also before you put this on you want to make sure your valve is turned counter clockwise
all the way so that the pin is not going to press on the schrader valve immediately, but
than after you attach it than you want to turn this clockwise so that the pin that’s
inside here press on the schrader valve and there I don’t know if you guys heard it that
just opened the system to our ac manifold gauge set. Alright so we come back up to our
pressure gauges and as you can see on the high side now we have about 75 psi of pressure
on this side and this is going to be considered your static pressure which means this is the
pressure you have with the car sitting turned off and the compressor not engaged. Alright
next I am going to connect the low side which is back here. Alright as you can see we’ve
got about 60 psi of pressure on the low side as well which is pretty close to what on the
high pressure side and this is what you want to see. So on this board I’ve drawn up two
types of common ac systems that are out there, one type is the one that has an expansion
valve and the other type is the one that comes with an orifice tube instead and what we have
on this car is this system here so we got our ac compressor which is this guy here which
compresses the refrigerant and starts the high pressure side of your ac system which
goes from your ac compressor to your condenser and from there to your receiver drier and
than your expansion valve and than after that is the low side of your system which is the
evaporator, which is the one that’s inside your dash inside your car with your blower
motor inside there blowing over it and than the return line that goes to your ac compressor
so this is the low pressure side on this system and everything in red is your high pressure
side. Alright so if you attach your pressure gauges to a car that’s been sitting for a
while the pressure on both sides should be fairly close to equal because once the compressor
is turned off the pressure equalizes on both sides, the pressure leaks from the high pressure
sides to the low pressure side and without the ac compressor running one side is not
going to have more pressure than the other but if you attach your pressure gauges and
this side is alot higher than the low side than that means you have a clog here that’s
not letting the refrigerant to slowly get back into the low pressure side equalizing
the system and that usually the culprit for that is a clogged orifice tube if you have
this system or an expansion valve that’s stuck closed. Now unless you have a completely clogged
orifice tube or an expansion valve that’s stuck completely closed, it’s not very common
to have those numbers with the ac turned off and the car not running. Get in your car and
turn on the engine, turn on your fan all the way to high make sure you’re in maximum cool
and turn on your AC. Next you want to wait a few minutes and with your AC compressor
clutch engaged you want to take your measurements and as you can see on the low side we got
about 15 17 on the low side and about 120 on the high side. So next once you get these
numbers you want to look into your repairs manual and compare those numbers to the numbers
you are supposed to have given the temperature and the humidity at the time you took the
measurements. But here are some very general numbers that could guide you to try to diagnose
problems with your car. Alright so here today our temperature is about 68 degrees fahrenheit
and our relative humidity is above 40% and the pressure we are looking to get at the
low side should about twenty five to thirty seven and the high side should be about eighty
three to one fifty five. Alright so according to the numbers we got earlier we are definitely
on the low side for the low pressure side and also on the high pressure side we are
towards the low side as well which basically means we are simply low on refrigerant. And
that about sounds right because on this car when you turn on the ac you don’t get cold
air you just get slightly cool air coming out of your air vents. Alright next lets talk
about different numbers that you could get on your gauges, so if your numbers on the
low side and on the high side are higher than what you are supposed to have than that would
indicate that you either have too much refrigerant in the system or you could have air that has
gotten in your system as well. Also if your ac condenser is unable to cool the refrigerant
that’s passing through it, either because your ac fans are not coming on or junk and
dirt and debry that could be logged in front of it and not allowing air to pass over it,
than again you could potentially be high on both sides as well. Alright next lets say
if you get about the same numbers on both sides, and if you are getting the same numbers
on both sides with the air compressor running in other words your ac compressor clutch engaged
and you are still getting the same numbers than that’s going to mean basically your compressor
is not doing it’s job which basically to compress the refrigerant , to take refrigerant from
one side suck in refrigerant from the low side and compress it into the high pressure
side creating low pressure on the low side and high pressure on the high side and if
it’s not doing that than that probably means it’s shot and needs to be replaced. Alright
so in the next scenario we are going to say that the numbers for your low side are lower
than what they are supposed to be and the high side are higher than what they are supposed
to be. Alright so if that’s the case you more than likely have a clog in your high pressure
side which is basically blocking the refrigerant from passing to the low pressure side raising
the pressure on the high side and lowering the pressure on the low side, the main culprit
is going to be if you have a system with an expansion valve the valve that’s stuck near
the closed position or a clogged receiver drier, now if you have a system that has an
orifice tube instead of an expansion valve than the main culprit is going to be the orifice
tube, see on this system you don’t have a receiver drier on the high pressure side but
instead you have an ac accumulator on the low pressure side. Alright so next lets talk
about the trickiest set of numbers you can get while diagnosing an ac system which is
too high of a psi on the low side and too low on the high side, if this is the case
if you have an expansion valve set up than that could potentially be your expansion valve
thats stuck open or near the open position allowing too much refrigerant to pass through,
or a problem with the check valves inside your ac compressor, see these check valves
like on the low side they only allow refrigerant to get in and not get back out and on the
compressor side or the high pressure side they only refrigerant to get out and not get
back in. But if like this check valve is not opening enough or it’s kind of closed than
you are going to build up too much psi on this side but more likely culprit is going
to be your expansion valve stuck near the open position. Now if you get these numbers
on a set with an orifice tube than, see it wont be your orifice tube because an orifice
tube just has a set opening or a set orifice you could say which only which is not adjustable
so it can’t be stuck open like an expansion valve so the culprit is going to be either
your ac compressor or your ac accumulator if its clogged would raise the pressure on
the low side and therefore lower the pressure on the high side. Alright enough of that so
now let me show you how you can use this to add refrigerant to your car’s ac system. So
obviously you’ll need a can of refrigerant you’ll also need a can tap like this and the
way this works is that you’ll screw this on the can and than once you screw in this valve
there’s a needle at the end of it that’ll come out and puncture the can opening up the
refrigerant to the valve and this is going to be connected to this yellow line here and
than from here we are going to open up the valve to the low side and than that’s going
to suck in the refrigerant through this line and the can to the low pressure side. And
once again when you are screwing this on the can make sure this valve is turned counter
clockwise and it’s in the open position and next we will screw on our yellow line and
than we start turning this in. Alright so once again we are going to get in the car
turn on the engine and turn on the ac and come back here and open up that valve that
will open up the system and suck in the refrigerant from the can through this yellow line and
the blue line into the engine. Alright so turn this counter clockwise and you can turn
this upside down to help with the flow, and here is a closer shot and you can actually
see the refrigerant and all the oil that’s in that can pass through here to your low
pressure side. Alright with our can pretty much empty we are at just about 25 on the
low side and just above 150 on the high pressure side which is about right, and now we got
really nice cold air coming out of these air vents, awesome. And that should about cover
it guys hope you enjoyed this video, if you did do me a favor and share it with your friends
and family on your favorite social network whether it’s facebook twitter or instagram
and also join me there I’ll put a link to my pages on those networks or platforms right
bellow this video, and especially on instagram I just opened my page there and I really like
the platform there so if you want to communicate on there and if you have an instagram page
go ahead and add me there I’ll also put some links to other related video’s on this side
of the screen that you can click on there will also be links in the description down
bellow. Alright thanks for watching I’ll see you guys next time.

About the Author: Michael Flood


  1. Sir I am experiencing a problem with my Toyota Yaris (2008) Aiconditioning. When I am running around 60 – 80 kph (let say 2 for 2 minutes) the AC blows hot air in the air oulet, and when I reduce my acceleration or in Idle position the AC works perfect.
    I already recharge/flush system with fresh 134A, replaced the receiver/drier. All gauges are working fine during idle position of the car (low and high side is perfect). My compressor is only 9 months old so i dont see any issues with my compressor.

    Hope you can share your experience with me. I am from Qatar. thanks.

  2. Yeah, that $10 deposit for Cali AC cans is annoying… On my trips there, I'll just grab some AC cans in Vegas if I need them in SoCal. You can't sell 49 state AC cans in Cali, but you can import them from other states for your own use… Yet another crazy California regulation…

  3. Hi, I tried the refrigerant, but still not cold air is coming from the vents. I think there is something wrong with the compressor. Belt is not running on AC. Any ideas on how this can be fixed. I don't want to take the car to the store and pay lots of money for repair. Thanks.

  4. Good explanation. I would suggest using the refrigerant to flush the air from the charging hose before allowing it to flow into the AC system. There is a valve for that purpose on your manifold gauge set. Sometimes you don't get away with turning the can upside down and allowing refrigerant to flow into the system in the fluid state. I'd keep it flowing in the gaseous state just to be safe.

  5. After watching numerous other YT videos on this subject, I found that yours is the only one to logically explain the steps to topping up the refrigerant. You were the only one to mention the IMPORTANCE of making sure the valves are in the correct position BEFORE attaching to ports (and can of refrigerant). Excellent! The best presentation yet on this subject! Keep up the good work!

  6. I am trying to diagnose my 2000 Mustang GT A/C problem. I have been searching for hours and I cant find a video that has my specific issues combined with my troubleshooting results. You videos are very informative and I was wondering what you think. The A/C blows warm air and the compressor clutch is rapid cycling. My low and high pressure switches ohm out correctly. Manifold gauge readings are @80/80 static (80 deg F 30% Humid). When the A/C is on the gauges read 20-60 on the low and 100-125 on the high. If I jump the low pressure switch, to stop the rapid cycling, the compressor runs continuously and the low side goes to 0 and the high side stays at 100-125. Bringing engine rpm up to 2500 never increases pressure. Gauge pressures are unaffected by rpm. No obvious leaks but I have not leak tested yet. I'm narrowed down to a leak causing low charge or the compressor is bad. Any advise would be appreciated. Thanks for the great videos

  7. Quality of the refrigerant is also that important? Everywhere you go you find made in China or India and on the can it says nothing about standards of quality.

  8. Question: I have a 1998 Ford Mustang GT. My A/C clutch stopped running. I watched one of your videos that stated that I could add refrigerant using the Low Pressure port. I purchased a kit which included a gauge. When I connected the line to the Low Pressure port, the gauge showed 150 PSI. My understanding is that the pressure should be between 0 and 35 PSI. What could cause 150 PSI on the Low Pressure side of the A/C system? I am afraid to "add" refrigerant due to the extremely high pressure…

  9. on the dynamic pressure reading with the ac system on and truck running and the compressor running. . my pressure gauges fluctuate from 18- 40 low side and 200-280 high side like ever 15 to 20seconds. I just install a new compressor orifice tube and accumulater so. the temp on the front air vent will show 60degrees F. …. So is this normal?? or is the pressures suppose to be constant.???

  10. You did not bleed out the air from the yellow hose before turning on the low side to allow the 134 into the system.


  12. great video partner love all your video's I think u forgot to purge your charging hose yellow one, but great explanation!!!!

  13. good job i got question what would be the problem if my system does not suck out freon out pf the can hi and low pressure 80psi with ac rinning thanks paul

  14. I have a 93 pajero 3.0l v6 6g72, its has a r12 system, I`m going to regas it do I have to change the compressor oil? or just buy r134 and fill it, tested earlier no pressure at all, gave to a mechanic to do timing belt think he disconnected ac instead of just moving to the side.

  15. ilike ur videos
    what the normal value for both side pressure when compreser engage .
    and what the normal value when compresser disengage for both side pressure ?

  16. I connected the gauge and got readings, afterwards when I disconnected the hoses the high side hose had refrigerant in it. I did everything as you showed in this video. Then I re tried it to see what happens and the same thing happened. Any ideas why?

  17. You forgot to purge the yellow line
    I'm glad that's not my car
    Now the refrigerant is contaminated with air.

  18. great stuff question my high side is close to where it should be but the low side is 17psi but when adding R134 low psi doesn't change

  19. Hey there. Good vid. ? I have a 30Ib jug of 134a. How would I charge my truck from scratch after my vaccum is complete?? Do I dump in the gas with jug down (liquid) from the high side or do I dump in jug up (vapor) through the low side port. Thx again!

  20. please help me.
    my car is a 2009 Toyota corolla. (clutchless compressor)
    my compressor takes less than half of the 12 oz can of refrigerant (which seem extremely little) before it max out and won't take anymore.
    low side jumps way above 50psi while the high side won't get any higher than 80 psi.
    I already replace the compressor control valve and pull a vacuum.
    bad compressor or clogged line?

  21. You have good communication with our minds , Thank You

    Just one thing
    How we can get the temperature schedule ?

  22. On the manifold between the blue and red knobs and just above the yellow hose, is that a window or is it for a connection of some kind?

  23. Question, by connecting the manifold gauges and hoses woud it not cause a pressure drop in the system?, and affect the measurement we are trying to get?…

  24. what's the problem when these happens?
    Low side too low — Hi side too high
    Low side too high — Hi side too low
    Low side too high — Hi side within a range (my case 50 psi on low 225 on high, blowing warm air, compressor runs non stop)
    Low side within a range — High side too high

  25. Oh, I charged my system twice and each time forgot to purge the yellow line. Is it going to be a trouble. I am in medium humidity area.

  26. what if I open the low and high side valves on my manifold gauge when checking ac pressure.but not charging the system.

  27. When you got your final readings, the clutch engaged and the pressures changed. Are you supposed to get them with the clutch engaged or disengaged?

  28. Now the question is why the system was low on refrigerant, refrigerant doesn't consume so this has to be a small leak somewhere.

  29. Thanks good video! But, How do you know the amount of the refrigerant that is delivered to the system is optimum so that the system would function as it was designed to have optimum sub cooling liquid and overheated amount of vapour in the system?

  30. Question: Pressure readings when to record them? The gauge records a low number and a high number. Which one do I use? I can hear the clutch "click" and the low number PSI increases. Example: Low side is 25, then increases to 68. It then decreases to 25 again, repeating the process. Which numbers do I use to assess the system? thanks "yours"
    Please reply at [email protected]

  31. I did not see you crack the vacuum line, that's the yellow line. Connect the can, and then the line is full of atmospheric air. You bust that air together with refrigerant into the system? Looks like yes. You are supposed to pressurise the yellow line, then crack it a bit open up there at gauges, for a bit of refrigerant to escape, which busts the air out. Tighten back up. Now you can open the low side to charge!
    If you think you are a profi, then be a profi, not just a garage dude!

  32. My gauge set connectors don't work. One has a spring problem, and the other locks but doesn't seal, leaking freon in the process. Should I replace these cheap connectors?

  33. Based on my understanding, the valve on the high-pressure side should also open facing down instead of facing up. Because the AC compressor draws freon from the low side to the high side, if the valve open facing up like in the diagram, how come the valve get open?
    I hope some one or the author can help me understand. Thank you!

  34. R / W, if the below comments on "bleeding the lines" is accurate (makes sense to me) you should edit this video otherwise you are not being very responsible with your advise . I am not trying to be an ass, I have learned a lot from you, but I am really glad I read the comments before attempting this.

  35. what are the temperature scale on the gage for on the low side 90degrees line up with 105 psi and it should be 45-55 psi and the T fitting on the yellow hose has a cap if I take the cap off and store the other end of the yellow hose there like I see you have it do I have put the cap back on when I use the gage  thanks for your help Bert

  36. Are the couplers that connect to the car the only ones open? Meaning the ports on the gauges are closed since you aren't using a vaccum

  37. Dear RNW you are great and you take your time to explain things well. But I have Question about my system which is confusing and I have not seen solution to it on you tube Maybe you can Help. I have Tundra 2001 it had front right side body damage affected the fender, RF headlight and air filter housing and bent the condenser, also replaced the Radiator, and fan was broken also. All were fixed. System had pressure even after accident. First situation was Low pressure low (15-20), and High pressure High over 250psi, and clutch engage and disengage frequently we added Freon just a little high side went way up and low stayed the same, pursuant to Toyota Diagnostic table, indicated Blockage in the Receiver Dryer or expansion valve, we replaced both, we also tested all the line connection for leak, after replacement and testing condenser for leak we got to situation 2. Now the condenser have minor bent but holding pressure, the low is steady normal at 40 psi, and the high side went too high 275 and kept increasing to about to 350- to 375 close to 400psi and we did not even put one small can and clutch engages all the time without stop. Do you suspect the high pressure sensor not closing the circuit and causing all of the issues?

  38. Hi my friend again! good explanation…..
    Question ?
    So how do you know is empty or how much refrigerant is in the car.
    Because you just put one can only,

    is a way to know how much refrigerant is in the car?

    thank you!……i am confuse……because you put only one can and it was smaller can…..thats right.
    thank u…..

  39. the book with the pressures you used relative to the temp/hum where did you get it i would like a chart like that to have for diagnosis thanks.

  40. I just added 4 oz of refrigerant oil to the compressor and the recommended amount of ac oil to the drier/receiver, but not to the evaporator. Now, I’m going to recharge the ac system with refrigerant. Do I still need to add more ac oil?

  41. What if it's within the number? My low side 30, high side 145, weather 73F humidity 75,

    Does that mean I'm low on freon? My ac blow warm air when rpm over 1500. I did removed a shim from the clutch after watching a few videos but that didn't help.

  42. Excellent video…with just one error. You did not show to purge the yellow line of air when you added the 134a.

  43. Great job on the video. I love in-depth tutorials that make sense! Too many people are out here making repair guides that don't understand what they're repairing and working on. Great job my friend!

  44. What would be the symptoms like,if you over charged the system ? Would the AC turn on and off rapidly ?

  45. you dident purge the yellow line before u let the 134a into the system so u also let a yellow line full of air into the system as well.

  46. My ac clutch on my 2013 Optima is spinning when on but the compressor does not come on. If I disconnect the low pressure switch, I hear the compressor but it is very faint. I try engaging the clutch manually by connecting 30 and 87 but I dont hear it engage.
    Pleas help.

  47. Questions..
    I changed my compressor, expansion valve, all O-rings, flushed my system and refilled my system with the correct amounts of oil and R134a. There were no leaks, all seems well with 2 exceptions. It takes a few minutes before it starts cooling and once it cools it seems like it isn't cold enough. I made sure the exact amount of R134a & Oil went back in the system.
    1) Should I add a little more R134a?
    2) Would the new expansion valve cause it to delay cooling maybe due to it opening slowly or something?

  48. I've always been taught never to turn the can upside down and let liquid into the low side. That is only for when doing a fast charge on the high side. Which I haven't learned how to do, but would like to. I just set the can in some warm water to speed up the charging. I think the danger is a hydraulic lock in the compressor piston if liquid gets into it. It seems like lately the most common failure is the compressor. There are so many junk new compressors on the market it's hard to find one that works, or lasts very long.. The OEM ones are probably the best bet but the cost is hard to justify in an older used car.

  49. You gave a few scenarios except one. What if the low side is right where it's supposed to be but the high side is too low?

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