What Pressure Should my Car AC Be - How To Check Automotive R134a Air Conditioner - Recharge Tips

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In this video I show what the typical AC pressures should operate around for a vehicle using R134a refrigerant. I also talk about my recommendations for finding and fixing leaks as well as a few tips and tricks.
Thanks for watching and subscribing! As an Amazon affiliate I earn from qualifying purchases. Thanks for your support!
Blessings,
Ben

[@eddiew2424]

I have been in the auto A/ C business for 48 years the use of a/c Dye is the best way because 75 percent of the leaks in auto A/c is intermittent due to expansion and contraction of all the aluminum parts and all the hot exhaust and water temperature repaid change I have the best sniffers that you can buy and use it first but most of the time we have to install a/c dye and bring it back at a later date and let it cool down and take all the plastic covers off put it on the lift and find the dye . We repair several hundred A/C jobs a season that is all we do

[@Cleofizoid]

One period 😂

[@BenjaminSahlstrom]

Thanks for sharing your expertise. I'll have to try out the dye option in that case. What brand/product do you recommend for the dye kits?

[@Dave-ei7kk]

Does someone make a UV dye for AC systems in cars like the leak-finder dyes you can get for engine oil or antifreeze?

[@DutchStar]

@@Dave-ei7kkJohnstone sells UV dye formulated for hvac and refrigeration systems.

[@Know-Way]

I had a leak in my AC system, turned out to be in the evaporator. What a PITA. It was my first ever A/C repair and after some research, I bought a set of cheaper digital gauges. The digital gauges can calculate superheat and subcool internally, and allow for switching between automotive (R134A) and residential (R410A, etc) refrigerants for the calcs. I found most analog gauge sets have dials for one or the other. I used dye in the system. A leak detector may have been useless because the evaporator is inaccessible behind the dash. After a month or so, I saw signs of UV dye coming from the evaporator condensate drip/drain line under the car. I can't confirm, but I read somewhere that some car manufacturers put dye in the system at the factory from new. I had to add R134A about once every 6 months before fixing the leak. The method I used was to first verify that there was a large difference between superheat and subcool temperatures. Then slowly add refrigerant until the superheat and subcool are within about one degree of each other. Typically it took about 2/3rds of the factory charge.

[@tonywahab3523]

Thank you for CLEARLY EXPLAINING how recirculation and ambient temperature affect the pressure reading on the manifold gauges! The chart that you share at 2 minutes is a valuable resource that will be very helpful. Those areas had me a little confused until I watched your video.

[@erikj9962]

I used this method minus the scale for my '07 BMW a few years ago and it's been working well ever since.

[@lilo2469]

When Ben Speaks, I LISTEN 👍

[@craigallenbeckett]

Great video, I would like to see more car stuff, ie finding leaks and repair.

[@ennardplushproductions8187]

Thanks Ben....great & Informative video

[@HVACTechMechanic]

I've been doing HVAC for 8 + years now. Car HVAC systems used to come pre-charged with dye. So yeah, dye is designed to be in the system. Dye is one of the best and easiest ways to find the leak. It mixes with the refrigerant oil and is A-OK to be in the system

[@DELLISTX]

WELL DONE! Car Guys should watch this just to refresh their memory. Save this video to watch, the only thing I would add is to use goggles when working on the AC.

[@craighansen7594]

Eye protection yes, gloves too. Refrigerant will give you a cold burn on unprotected skin.

[@briancarlisi2224]

All car compressors are designed to leak a small amount of refrigerant to keep the outer seal pliable. Adding several oz every few years is not out of the ordinary. Also, good mention on checking condenser’s coils for blockage. Many times on very high mileage vehicles (200k +) the condenser’s coil fins are smashed closed. This will cause the high (liquid) side pressure & temp to run much higher than normal. May need a condenser replacement or lots of patience in straightening the fins to allow proper air flow/ heat transfer when high pressures/ temps seen on liquid side.

[@fauxque5057]

If you draw down a vaccum forget about trying to reach certain pressures. Always go by weight. Get a cheap digital scale and if the system requires 34oz give it 34oz and ignore the pressures unless they are sky high

[@frankconte5545]

Great video as usual....FYI not only do the automotive quick disconnects make it easy to connect, they usually have open/close valves right on the quick connect hose fittings so you don't actually depress the schrader valve until you turn the knob in after your connected...

[@BenjaminSahlstrom]

Must vary by set type as the ones I've used immediately connect and don't have a separate option of depressing the valve core.

[@frankconte5545]

@@BenjaminSahlstrom yeah, that's true...afaik they are add on so they can be bought separately to just screw on to the ends of your gauge set hoses if it didn't come with them. 👍

[@Barryd57]

When I attach the quick disconnects, I make sure the needle in the quick disconnects are fully withdrawn so it doesn't push/open the Schrader valve. Once it's connected, I turn the handle in so it opens the system and allows gas to flow. If you didn't buy gauges with handles, replace the set.

[@GreyRockOne]

Nice work Ben, I've done my research, did everything by the book and had fantastic results, even after replacing components like an evaporator, (NO easy task in today's cars). I use all OEM parts, proper oil and amount, system evacuation and such. I also had no R134A to reclaim so that wasn't an issue. I even have a scale to measure the refrigerant. One thing I noticed on your setup, looks like you did a liquid charge vs a gas charge, when is one desirable over the other? I'm also with you on the sniffer over the dye.

[@Barryd57]

If the jug is inverted like Benjamin's example, you can overwhelm the system by introducing too much R134a so monitor the low side head pressure carefully.

[@MrRikkitikki]

Add Slowly and it will flash to vapor before it gets to the compressor.

[@seephor]

I was going crazy trying to find out why my high side was so high that the safety valve in the compressor was releasing refrigerant. I replaced expansion valve, condenser with no luck. I was about the give up until I decided to check the radiator fan. Turns out I replaced the fan a couple months ago and never checked the direction of the airflow. It was reversed so it was blowing through the radiator then the hot air was hitting the condenser which was heating up the refrigerant and causing super high pressures. A reversed radiator fan can cause high side pressures to be insane. A simple wire swap fixed the issue.

[@jima3129]

How in the world was it running backwards? You mean the plug could go either way????

[@seephor]

@@jima3129 The fan motor I ordered off Amazon had the red/black wires swapped on the plug. I assumed it was correct since it was basically spinning and never checked the airflow direction. Never assume with aftermarket parts.

[@jima3129]

@@seephor Amen to that my passengers side window still works backwards. Lolol not as catastrophic as your case.

[@SixTwoHemi]

Excellent video 5 ⭐️

[@Martinpreciado1]

Thanks for clarifying the ambient temperature. Most videos say the pressure should be between 25 and 30 on the low side when recharging and about 190 on the high side and they don't say anything about the ambient temperature. The temperature here was about 102 degrees and my pressures were high around 40 for the low and 210 for the high but I had barely put any from a 12 oz can. It was still not blowing cold air. I put in some more and it started blowing cold air now my high is around 250 and the low still around 40. I will check it at a lower temperature later to see if it has a lower pressure. I was afraid it was too high. Maybe it needs some more.

[@bobbyplatt7654]

Good info sir thanks..

[@MichaelMantion]

When testing the car take the temperature close to the Condensor. Ijust because it 75 degrees out doesn't mean the fan is Circulating 75 degree are. It's likely warmer. The other option is doing it when it's windy or use fans to move hot air away from the condenser. Oh and I know with R134a prices going up don't use propane. I yes it works better, but is flammable and you need a lot less and you would have to accidentally vent all the air to the atmosphere.

[@publicmail2]

All compressor will leak at shaft seal. Always add a PAG oil charge (walmart) especially if leak is low and leaking oil too, without oil compressor will fail. If you need to add 12oz a year system can last indefinitely. To fix a leak and evac system diy'er doesn't have equipment and more parts may have to be changed also.

[@Terrapinstation20]

Thanks

[@genehart261]

Use a thermometer at the vents, add very small amounts of refrigerant. One or two ounces at a time.

[@ricks88s]

Thank you Ben.. Sure enough the cabin filter was clogged with leaf debris . Thank for the smack in the back of the head...I should of thought about it but didnt know that the van had one behind the glove box.. Fixed.....

[@erickfranklin4675]

I need some of those auto ac guages

[@jgarcia9527]

You showed the connections and where the each hose/connector go, but did you opened both valves or just the low side??

[@paulthompson1654]

Pressures are dependant on clean evaporator core clean condenser condenser fans working orifice tube or Tx valve variable displacement maybe ecu controlled fixed displacement When charging use weight method with scales u did excellent pressures are almost are individual to each model pressures are changed by design or fault if correct charged The ambient temp can change pressures have all doors open when charging to load a/con have on recirculation ,, sucking in air from engine bay is not normal check pressures at idle and 1500rpm THE PRESSURE CHART IS WAY INCORRECT 115F DAY 25--35 PSI LOW ,,, 150--160PSI HIGH at idle and 1500rpm txv and fixed displacement compressor

[@konstantinusstoyanov9749]

Don't do AC but interesting, thank you

[@rantanplan1911]

In my Subaru's factory service manual it says to set recirculation to ON and open all windows. I would really like to understand why this all matters. Thanks!

[@traviskelly7082]

I work on MVAC, fan speed always on max and put recirculate on...ALWAYS. The same with a house do you open a window when you're charging a house? JS lmbo. Now as far as dye, it works well and I find it better than a sniffer just my opinion and if your look for a leak with dye if you don't want it in there flush it out, I mean once you find the leak you have to take the freon out anyways to fix it. I honestly think you did well even with a scale. I don't use scales I use a temp gauge and if it's a healthy system I can get normally 39 to 42 degrees coming out the vent. as of 2024 this will be the last year you can buy it everything goes to 1234yf. Be good bro

[@garrettstevensen2467]

R134 not available after 2024?

[@traviskelly7082]

@@garrettstevensen2467 nope, all gone

[@traviskelly7082]

@@garrettstevensen2467 Remember how they did R12? doing it the same way.

[@petem6291]

The last few 30 lbs 134A 😅 I bought came with dye in it ….

[@TroyD-vo1bz]

Hello Ben: So I have a question that I believe is closer to your area of expertise. I have a mini split, but it is a 24 volt system that uses a variable frequency compressor that I use in my RV. These are designed to be energy efficient, but they probably don't produce the same kind of output as a traditional one speed compressor would. I can tell when the compressor is at max speed just by the sound, and I can also confirm by the wattage being used. I'm assuming that low pressure and high pressure readings are only valid when the compressor is running at full bore--correct? For an automobile I don't think this is even a factor, the compressor is either on full output or off. Since the head unit or evaporator is indoors (Inside the RV in this case) I'm assuming I should be using the indoor temperature and not the ambient temperature outdoors. Alternatively I guess I could open the doors in the RV so everything is the same. Since this test is based on ambient temperature, this seems to be a critical factor so I wanted to ask for your suggestion. In my experience with this mini split, it only produces the extreme cold temperatures very briefly when the compressor is at full bore, and then it's cycles back down again. I think this is a trade-off for energy efficiency as this runs off a battery. Nevertheless, all the more reason to get it as cold as possible. Again I just wanted to ask about where I should be taking the ambient temperature reading, because I'm talking about a mini split, and then I'm also assuming that the pressure is only valid at full power on the compressor. I've even seen guys with automobiles rev the engine up to 2500 or so to get the readings. I think you're just using idle speed, so that part is a little confusing as well. Isn't pressure going to go up on the high side with higher revs and the low pressure lower? I don't know which one is correct, but most Mini split systems only have one speed. My situation is a bit unique here with a variable frequency Compressor, but I think the basic concept remains the same. Your comments and feedback Appreciated.

[@timmytool1231]

I've got a situation on my 2016 F250, 6.2 gas. This year for the first time 137k miles, when I come to a stop the AC heats up, as soon as I get to speed it cools down. My gauge showed low on R134a, so I added some not much, and the pressure was ok. But still the same situation happened. I don't have a condenser fan, just a cooling fan. If you have an idea where to go next, I would appreciate it. Great video by the way.

[@MrRikkitikki]

Plugged condenser, no air flow at idle.

[@2nickles647]

Clean the condenser and the radiator. Wash both of them out with a garden hose. When I did my daughter truck. I used dawn dish soap. Used compressed air to blow out any remaining debris.

[@clarkbreen4634]

I usually recover the refrigerant and weigh in the correct amount

[@BenjaminSahlstrom]

Great method for sure. Eliminates all the environmental factors.

[@DELLISTX]

Please do a video on changing from R-12 to 134A, show all the steps and what all the pressure readings should be to get the 134A car vent temps as low as the R-12.

[@MichaelMantion]

R134a is getting phased out . There are a lot of R12 alternative, use to get them at auto parts stores. I bough a bunch a decade ago from Canada. you can still get Envirosafe online but the prices keep going up. You need half as much as your R12 system says and they say you don't have to vacuum the system. Eventually all the safety nannies will allow cars ACs running on R290 or R600a. Might take a decade.

[@Know-Way]

@@MichaelMantion "Eventually all the safety nannies will allow cars ACs running on R290 or R600a. Might take a decade." We can hope, but I think you're being overly optimistic.

[@royagservicesllc387]

@MichaelMantion R134A is not getting phased out. It is illegal to charge a R134A system with R1234YF. R134A will be around for a long time.

[@2nickles647]

They sell R12 to 134a conversion kits. Recover the R12 to an approved container. Weight the recovered R12. If there is any oil recovered, weight it too. Pull a vacuum on the system and close all the valves. Shut the vacuum pp off Record the vacuum reading. Go to lunch for 1 hour. Did the vacuum reading drop significantly or held vacuum. A decayed reading indicates a leak. Refill the system with nitrogen gas. Add dye. Replace the bad part and retest. If the system held vacuum. Obtain the specs for the vehicle you are working on, that will tell you how much in Oz to fill the system. Get a scale and add a can to the yellow line. Open the tap, depress the small valve 2 sec to burp any air out of the line. Open the blue or suction line and start filling the system. Start the vehicle. Set to max cool. The AC condenser cooling fan should start. Observe the AC clutch cycling as you fill system. Fill the system to the specs for the vehicle you are working on. Make sure the condenser is clean also. You may need to wash it out.

[@Bass.Player]

It's actually fairly difficult due to inside fan speed choice and outside condenser condition, fans and temperature. Don't run the inside fan at full speed but do run on recirculate. Recirculate is the only position that should be used unless the inside ambient temperature is above the outside temperature, this is what that feature is designed for. (Unless Bubba let's out a giant fart) Master Ase and IMACA certified instructor...

[@spelunkerd]

So, his advice (to not use recirculate while measuring pressures) is incorrect? In that case, what ambient temp do you use when trying to decide what ideal pressures are? Shouldn't your choice of ambient temp for looking at gauges be the same temp that is entering the evaporator? If you use recirculate, your ambient temp for the condenser will be correct, and the temp for the evaporator will be colder than ambient temp suggests, confusing gauge interpretation.... HVAC techs would measure temperatures at both coils and calculate superheat, but in the automotive world we don't have those fancy tools.

[@jima3129]

Do you ever clean under the hood? Dirt will wick plasticizer out of plastic parts, making it brittle and prone to crack, then you get leaks, then you have problems that are very hard to locate. I actually use a pressure washer to clean, and apply protectant like armourall to hoses and plastic parts. 2004 f150, 164,000 miles. Runs like a swiss watch. 😊

[@LTDan-pk3mx]

Dude, Please look into Aerospace 303 protectant for your hoses and even tires.. The stuff is Amazing!

[@jima3129]

@@LTDan-pk3mx thank you I've been using armourall.

[@Gruin]

Look into "Strike Hold" Dry Lubricant Protectant, see their Video, can be Sprayed Directly into Electrical Componants while Running. Alternator, Electric motors, battery Operated Equipment, Generators, Excellent for Firearms.

[@CaptainSteve777]

Good video. Is there a rule of thumb for what the equalized pressure should be if the engine is off and cool high and low equal)?

[@2nickles647]

Approximately 50 to 65 psi

[@datsuntoyy]

I saw your pressure chart that shows about 340 psi at 100 degrees. I've found quite a few charts that show 100 degrees closer to 120psi and that's more inline with what is on the front of my manifold set. How do you know which chart is correct? The app from the Freon manufacture (chemours) states about 135. 135 seems low to me but who would know more than the one who actually makes the refrigerant? Edit: finally charged. 2,000rpm. 40/365 with 128 degree condenser air inlet temp. 158 degree high side line temp at pressure tap. Upon test driving, 40 degree outlet temp.

[@brucesimpson8579]

Adding the refrigerant every 3-5 years seems the most practical solution for Ford vehicles.

[@mr_mnky]

What tips do you have to diagnose & fix an overcharge condition?

[@MrRikkitikki]

Recover all the refrigerant and weigh in the correct amount.

[@marconantel7735]

So I’m guessing a 50-60 degree condensing temp then? And an evaporator temp of 35-55?

[@markyakubovsky3380]

Hey Ben, Rookie question- I noticed some of the manifolds like yellow jacket and Mastercool don't have the sight glass on them, but they look sturdy as hell.. Is the sight glass needed for pulling a vacuum etc?? Thx

[@MrRikkitikki]

No

[@jake-mv5oi]

I always add dye. Best way to find slow leaks IMO.

[@jbichl]

Can you use 1 set of gages for different refrigerant types?

[@MrRikkitikki]

Yes to read pressure only. Careful of cross contamination.

[@natedawg4997]

With the tank upside down like in the video, does it matter if you charge through the high side or the low side?

[@MrRikkitikki]

Yes, always charge slowly to low side.

[@coyoteserranoband]

When doing a recharge with a manifold set- I'm guessing keeping the high pressure coupler value should be open? But the high pressure value on the manifold is always closed while the vehicle is on + compressor on. Is this correct?

[@2nickles647]

No, both valves are closed. Never open the high side valve at the gauge set. You can blowup the can.

[@coyoteserranoband]

@@2nickles647 it didn't! I wonder why?

[@flemsnopes3135]

I'll evacuate the system and put 100 psi of nitrogen to it, then squirt a solution of water and Dawn soap on the hoses, connectors, compressor seal area and condensor with an ordinary spray bottle. You'll see the problem area quickly where you see bubbles.

[@2theCore777]

What about if one car takes 850grams of refrigerant & another only takes 450grams ? Is that pressure chart accurate/universal for any charge of refrigerant or a particular charge ?

[@watchdogu.s.a.8973]

The chart should be accurate regardless of the amount of refrigerant a particular system is designed to hold. The pressures should measure/register based on the ratio of refrigerant to the overall volume and based on the ambient temperature. I'm not an actual A/C tech but I have stayed at Holiday Inn Express a few times.

[@johnlim6108]

Hi sir. I have a three doors True cooler that uses R134A gas. If the temperature in my store is 75 degree, what should the low side pressure be? Please help. Thank you.

[@MrRikkitikki]

Temperature in the store does not matter. Temp in cooler tells the story.

[@AndrewCoutts]

What RPM should I have the vehicle at? I notice a huge change in pressure at idle (~950rpm) vs 2000-2500rpm.

[@2nickles647]

Should be idling.

[@davids7550]

Be very careful about keeping AIR out of your system. Purge your gauge lines before hooking them up. I actually installed ball valves on the ends of mine to keep them completely sealed. The Schrader valves are a highly likely source of refrigeration leaks. They should probably be changed out if there is any significant leak in your system.

[@abdalqadr1]

❤❤

[@TwoHemiViewer]

I would like to buy some cans of R134R and sent to Australia

[@MiamiWebDesign]

My truck's ac blows cold but barely to the point that I have to drive with my hands on the actual ac vents in order to cool myself down. The problem is that everything in my ac system is new, except the evaporator, all other parts have been replaced. My pressures show normal low side but high high side but in my case the orifice tube is new and shouldn't be clogged at all. What else can be the problem? Thanks!

[@2nickles647]

Evaporator core plugged. When the AC is running. The evaporator core will develop condensation. That's why it has a drain. Because of the condensation, if there is any dirt. That's cakes up the evaporator core.

[@Texasmule]

What if my pressure is at 80+ from what the AC pro gauge tells me

[@ronh5491]

What do you do if the compressor is not running because of the low pressure switch?

[@lordjaashin]

look into why low pressure switch is acting up.

[@marconantel7735]

It sounds like you have a leak. Best thing to do is pressure test with nitrogen, find the leak (s) and repair. Pull a vacuum on the system and refill with refrigerant

[@johnsutter1497]

Where can I find that chart ?

[@BenjaminSahlstrom]

www.rechargeac.com/how-to/ac-system-pressure-chart/

[@chrisasaurus]

I would recover and add nitrogen to find a leak

[@MrRikkitikki]

I always recover what is in the system and then weigh in the correct amount... No Guessing...

[@ManiacalMichael504]

Fords have UV dye from the factory.

[@BenjaminSahlstrom]

Seriously? Since when? That's super cool.

[@ManiacalMichael504]

@@BenjaminSahlstrom Not sure, but they've been doing it since the 90s as far as I know. The dye actually comes in the accumulator, and mixes with the compressor oil.

[@steveharding8965]

I just filled with a can and the aircon stopped working.I started bleeding from the low point seemed warm air was coming out,then suddenly cold gas and it started working again.Must have been air in the system.

[@2nickles647]

To much refrigerant

[@kxtreme1942]

3 Bar is to high on low pressure side. It should be 2 Bar. It is overfilled.

[@darrenveit7065]

So the only correct way to determine anything with wrong with the system and while I'm typing this I see you talk about over charging it don't ever do this it's not the more the merrier! And there isn't capillary tunes in a car ac unless it's like 50 yrs old

[@mariomata9177]

I put new lines and a condenser in the ac of my car but still not cooling down?

[@MrRikkitikki]

Must vacuum system properly before adding charge. Air is a contaminant.

[@2nickles647]

Was the lines broken? Condenser busted. Did you replace the metering valve that goes into the AC low press line ? Are the cooling fans running. Is the AC clutch cycling Have you changed the cabin filter

[@mariomata9177]

I did replace condenser and compressor expansion valve and avaporator too and Liquid Line still not cooling nothing

[@mariomata9177]

The compressor is working and fan, too. I changed the filters, too, but I am still not working. Just blowing warm air

[@bn880]

your low side gauge is busted/wrong

[@sivucit]

None of this temperature will work that you have described on variable valve compressor which is what all recent latel model cars after 2015 has it. The knowledge you have on residential will not work in Automotive because , fan speed, variable valve compressor , change in speed of air at condensor (based on car speed) all affect pressure and heat.

[@BenjaminSahlstrom]

Interesting. I suppose the only option in newer stuff is to just evacuate and weigh in the factory charge?

[@sivucit]

@@BenjaminSahlstrom I always evacuate and add charge as per spec

[@sivucit]

@@BenjaminSahlstrom for same reason super heat and subcool never works like residential and it also differs for every manufacturer

[@eddiew2424]

He is right variable stroke compressors work different can’t go by charts and pressure go by factory specific charge pump it in before you start the car a lot of the newer cars hold like .83 charge without a good robinair machine it is impossible to get the correct charge. And on the small units a once or two makes abig difference

[@JMAC479]

In the automotive world of A/C, dye is used 99.8% of the time and in no way affects reliability.

[@ianbutler1983]

Here is what I do that will horrify pros. When my A/C stops working, I stop at Walmart and blow a can onto my car. Than it works for a month or so. 2 or 3 cans a year is pretty cheap compared to A/C repair.

[@darrenveit7065]

Lol so much of this is wrong you really should have not made this video but I love it when people do this shit I end up with the car at some point and I make money!