What Should my AC Pressure Be?

ac pressureKnowing what the pressures are in the air conditioning system in your car can tell you almost all you need to know about how your system is functioning.  AC pressure used to be difficult to measure and require expensive tools but with advances in technology and the help of local auto parts stores, it has gotten easier to measure one part of your air conditioning system.

AC refill cans are readily available at your local auto parts stores and even at many larger stores.  Many of these refill cans come complete with a pressure gauge to help you discover a little bit of what’s going on in your system and to help you guess at how much refrigerant to dispense.  These gauges are relatively accurate and an inexpensive way to measure the low side pressure in your system.

Unfortunately, the low side pressure is just one piece of the puzzle.  Your air conditioning system is split in half when it comes to pressure.  Your air conditioning system holds a very high pressure between your AC compressor and condenser up expansion valve, and a relatively low pressure after the expansion valve and evaporator and back to the inlet of the compressor.

The can of refrigerant you purchased from the auto parts store is pressurized so it can push the new refrigerant into the system.  To make sure you get as much refrigerant out of the can and into your system, you connect it to the lower pressure side of the system so it is the low side pressure that you see measured on the gauge on your refill can.

To measure the pressure in the high-pressure side of your system, you need a little fancier piece of equipment.  The pressures in the high-pressure side of your system are so high that it requires special hoses and connections along with a special gauge to contain the pressure and ensure you don’t release any of the refrigerant to the atmosphere.  The best way to measure the high-pressure side of your system is to get the proper tools for a local auto parts store.  This set of A/C Manifold Gauges would work great!

Now that you’ve got a safe and reliable way to measure your AC pressure, you need to know what you’re looking for.  Pressures can vary from car to car based on the system and the pressure in your system will also vary with the ambient temperature.  The warmer it is outside, the higher the pressure will be.  For a general reference, you can check out this chart of R-134a system pressures.

If you find you’ve got a low pressure on the low side of your system, then it’s most likely that you’ve got a leak as that is a common problem in automobile air conditioning systems.  A low pressure on the low side could also indicate a clog somewhere in your system.  If you find a higher than usual low side pressure it usually is an indication of a failed compressor, but it’s also possible that your system is simply overfilled if you’ve recently added refrigerant.

On the high-pressure side of the system, a low pressure can also indicate that you’ve got a low refrigerant level or if the pressure is close to the same as it is on the low-pressure side it can confirm you’re having compressor issues.  A higher pressure here can again indicate your system is overfilled if you’ve recently serviced it, but usually, it is an indication of a clog in the system.

Most problems with your air conditioning system will require a vacuum, repair, and refill of the system.  Leaks, on the other hand, are problems solved simply by adding Red Angel A/C Stop leak & Conditioner through the low-pressure port in your system!

For more information on Red Angel A/C Stop Leak & Conditioner including how it works and directions for use, click on the banner below!
Red Angel AC Stop Leak & Conditioner

 

 

 

 

You can also find Red Angel A/C Stop Leak & Conditioner at any of our partnering auto parts stores like:

  • AutoZone
  • Advance Auto Parts
  • Bennett Auto Supply
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  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributer
  • DYK Automotive
  • Fisher Auto Parts stores
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  • Hovis Auto & Truck Supply stores
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  • Any Part Auto Parts
  • Consumer Auto Parts

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28 responses to “What Should my AC Pressure Be?

  1. I change the A/C canister, cause the valve to fill, was broken, so I bought a brand new one. I installed it, and I saw on internet I have to add oil in it before to fill it with refrigerant, but which oil I have to add, and how many ??? My car is a 1997 chevrolet Camaro RS 3.8 litre. Thank you !

    1. Louis-

      You would need 26 ounces of PAG 150 for your Chevrolet Camaro 6 cylinder. Feel free to contact our technical support line at 888-863-0426 with any other questions.

      Thank you!

      -BDP

  2. Hello…
    I have a problem with the a.c…
    A couple of weeks ago…
    My truck (2000 Chevy Silverado 1500) stop cooling off…
    Started blowing cold air but it wasn’t enough cooling like before… So, we tough that may be the gas (idk the correct name to called.. sorry) was finished, and yesterday I bought a a/c refrigerant I didn’t know how to do it, so, I asked for help to my uncle, and he helped me.. so on the way back of his house to mine ( like 1 or 2 mins away) was cooling perfect…
    Now this noon I tough that May b will be perfect… But my surprise that it was blowing hot air when I turn on the a/c..
    Now it’s not cold like before… At least before I was available to close the windows and feel a little bit of cold air.. but not now…
    So, I went back to my uncle house and telling him about the problem, and he told me that may be was that needs oil for the AC… Ok then I went to buy another refrigerant but now with oil or conditioner… and he filled out… But it’s not working… Still blowing hot air… and he told me that the air compressor it’s not working, so I have to change it!?!!! and while I was driving today (without the AC on… Super hot weather) I listened a wear noise like it was like a Lawnmower not loud but I can hear it while I was driving…
    I’ll appreciate your help!!!
    Thanks

    1. Sandy,

      Thanks for your question about your 2000 Chevy Silverado. Based on your description of the loss of cooling, it sounds like you’ve got a leak in your system letting the new refrigerant you put in escape again. Our recommendation would be to use Red Angel A/C Stop Leak and Conditioner (available here: http://store.gobdp.com/a-c-stop-leak-aerosol-00222/) to seal the leak, then add refrigerant until your compressor starts running again.

      Thanks again for your question!
      -BD Auto Pro

  3. I replaced my account compressor , acculalator and expansion valve, the oil chart said I needed 14 oz of oil and 58 oz of freon. I put 11 oz of oil and 58 oz of freon in it I ran my truck for awhile air blows cold but my high side pressure got to 450 low side was around 60. What’s wrong? Oh it’s a 2006 Ford expedition

    1. Chris,

      Thanks for your question about your air conditioning. Unless it was extremely warm outside, those pressures do sound to be a bit high. You might try calling Ford to find out what the pressures in your system should be just to make sure they are higher than normal. This could have happened if you didn’t fully evacuate your air conditioning system before you installed the new refrigerant and oil or it could be an indication that you’ve got some clogs somewhere in your system increasing pressure.

      Thanks again for your question!
      -BD Auto Pro

  4. Hi,
    I have 2007 sentra and it stopped blowing cold air this summer. I checked the low pressure and it always shows 100 psi even if the ac is switched on or off. Could it be a faulty gauge. I checked the same thing on my altima and it shows same air pressure. I am thinking it is definitely a faulty gauge. But wanted to check with you.
    I just checked pressure in my altima’s ac system after starting it and it is showing 25psi. This means gauge is working fine. Can you please help me why pressure in my sentra is 100psi and there is no cold air

    1. Kapil,

      Thanks for your question about your Nissan Sentra. When your AC compressor isn’t running, the pressure in your system equalizes between the high and low side. What that pressure should be depends on the design of your system and the temperature outside when you take the measurement, but 100 psi with the compressor off may be just fine. When the compressor turns on it should lower the pressure on the low side of your system and that pressure again is dependant on ambient temperature and other factors. If the pressure isn’t lowering in your system with the AC switched on, then either your compressor isn’t running, or it has an internal failure.

      Thanks again for your question!
      -BD Auto Pro

        1. Elijahhannigan-

          The most common cause for high compressor head pressure is clogging or contamination in one of the refrigeration lines. This can be caused by a number of different factors such as blocked air flow across the cooling coil, debris or water contamination, even high ambient temperatures. We recommend bringing the vehicle to an A/C specialist for a proper diagnosis.

          Thank you!

          -BDP

  5. I have a 2014 Nissan Altima. My mystery is as follows: My AC cools off ice cold while it is 80F or below but it blows not hot air but neutral air when it’s over 90F. I followed some DIY tips and assumed it was low on freon so I bought a AC Pro 20 oz can with a gauge on it. First measured the L pressure with the gauge on the canister and it showed overcharged before putting anything in it. I assumed the gauge may be a faulty one so I put all the freon in. Then I realized it stopped the AC blowing any cool air even when the temp waa 75F at night. I read some more DIY tips and decided to discharge and let some pressure and freon out. I did let out quiet a bit. However the gauge always read on the red mark. But the AC started cooling off again like it was before; meaning cooling off when outside temp is 85F or below and blowing neutral air when it is over 80F. Tonight it was 80F and then dropped to 75F at night and it was blowing ice cold air. I checked the pressure at 1am while it was blowing cold air. It showed in the middle of the green mark. Today it will be 92F and I know it will blow neutral air like it has been past 4 days. Since it’s cooling off satisfactorily at nights or when the ambient temperature is 80 or below, can I override the compressor issue, the leak issue and possible clog issue? Or What might be causing my AC not to cool when it’s 90+ outside but work when it’s 80 or below outside. What may be wrong? Thanks in advance

    1. Joey,

      Thanks for your question about your 2014 Nissan Altima. The most common causes of the problem you’re having are either an overfilled system or a clog in your system. In either of the situations, when the ambient temperature is high, it causes a higher pressure in your system and could be tripping it off on overpressure. You wouldn’t want to override this as it is a safety feature for your air conditioning system. Since you’ve now added and removed refrigerant, the only way to make sure your system isn’t overfilled would be to have the system completely evacuated then have the correct weight of refrigerant added. To check for a clog you would need to check the system high pressure when it was blowing cold air as well as when it wasn’t working.

      Thanks again for your question!
      -BD Auto Pro

  6. Hi, i have a 2014 passat. The pressure readings are as follows:
    LP side
    Ac off: 115psi
    Ac on: it starts with 80 psi and sometimes goes down to 35 and blows cold air. It may not make sense but when the outside temp i high 35 Celsius it blows cold air. When the temp goes down 27 or so Celsius blows hot and veey rare blows cold air. So with the ac on it fluctuates feom 80 to 35psi. Any idea???

    1. Nick,

      Thanks for your question about your 2014 Passat. The pressures you are seeing in your system could be within the normal operating range. Pressures in your air conditioning system will vary significantly with as ambient temperature varies so those could also be high or low depending on what the temperature was when you made the measurements. Since your system seems to work fine when it’s very warm out it could be that your system is a little low on refrigerant, but the symptoms you’re having could also be due to a clog which would require measuring the system high side pressure as well.

      Thanks again for your question!
      -BD Auto Pro

  7. I have a 2000 GMC Aerotech passenger bus. It has 2 ac units running off of 1compressor and the Freon evaporated after 9 years of sitting. The tag calls for 4lbs and 8oz of refrigerant to feed both units during simultaneous running. I added a can and the compressor kicked on but was hot. Added another can and it started to chill. Looked at the pressure and it was at 40lbs. Added a 3rd can and it was at 50lbs. It became cooler at that point, but not cold.

    Do commercial vehicle units require more pressure than your personal vehicles? I don’t want to add another can to get it cold and it messes something up. Mind you, the ambient temp was 93 degrees and my gauge was at the 85+ temp reading.

    1. Que,

      Thanks for your question about your 2000 GMC Aerotech bus. The operating pressures of an air conditioning system are determined by the type of refrigerant used not the size or configuration of the system. To get your system operating at top efficiency you need to first evacuate the system, then add the refrigerant. If there is a leak allowing the refrigerant to escape, it also allowed air to get in. Having air in your system with the refrigerant will reduce the efficiency of the system and change the pressures. We recommend getting the system evacuated then adding refrigerant by weight.

      Thanks again for your question!
      -BD Auto Pro

  8. I have a 2007 Kia Sportage that blows warm air when at a stop light or drive through. However, if I put it in park or neutral and throttle the rpm’s up to 2500-3000, it starts cooling again. When idle, my low side reads about 32psi and high side reads about 220psi. I have only checked it multiple times within the last two weeks when ambient temperature is near 100 Fahrenheit. Any ideas why it is doing this?

    1. Carlos,

      Thanks for your question about your 2007 Kia Sportage. Both of those pressure readings seem a little low for an ambient temperature of 100 degrees. You can try using this chart to see what pressures should be based on outside temperatures. It could be that your system is low on refrigerant since both the high and low side pressures are low. Also, it’s possible that your compressor is starting to get worn out since things work a little better when your engine is turning at a higher RPM but you would need to make sure you’ve got the right amount of refrigerant in the system before you could check for that.

      Thanks again for your question!
      -BD Auto Pro

  9. Got a 98 S10 my high pressure line is hot ..really hot .im in AZ and temps now are in the 105-110 range . She blows cold,air just wondering how hot is the high pressure line supposed to get ..can it be there is air in the system ..

    1. James,

      Thanks for your question about your 1998 Chevy S10. The high-pressure line between the compressor and the condenser will get very hot, too hot to touch, under normal operating conditions. The compressor raises the pressure of the refrigerant to over 300 PSI and all the compression adds a lot of heat to the refrigerant so that is perfectly normal. There aren’t any specifications for temperatures of the refrigerant entering the condenser as long as the refrigerant is cooled to ambient temperature by the time it comes out, everything will work properly.

      Thanks again for your question!
      -BD Auto Pro

  10. My 2007 Honda Civic was having cooling issues, so I bought a a/c refrigerant and topped it up. It came along with a pressure gauge for low port. I get very high readings when I have driven the car and low reading when the car is in shade or couple of hours. Which one is accurate?
    My AC problem had resolved for few days after I had topped it up, but now it starts blowing hot air after I have drive the car for few minutes. What maybe the problem here?

    Thanks in advance.

    1. Abhi,

      Thanks for your question about your 2007 Honda Civic. It sounds like you’ve got a slow leak in your air conditioning system since adding refrigerant helped it work for a few days. Use Red Angel A/C Stop Leak so seal the leak and keep your air conditioning system working properly. The low side pressure in your air conditioning system should drop down significantly when your engine is running and your AC compressor is cycling on. When the compressor shuts off or you turn your car off the pressures in the system will equalize between the high and low side so the low side pressure will read much higher.

      Thanks for your question!
      -BD Auto Pro

  11. Hi I have a Honda Brio and it met with a small accident which damaged the condenser needing a repair and then refilling of Cooling Gas. I had the AC pressure checked (Car engine running and pressure valves attached) and it stabilized around 32 in the ambient temperature of around 35 degree celcius. I wanted to understand in what is the desired AC pressure level for a Honda Brio car.

    1. Shail-

      Thank you for asking about your Honda Brio. At 35 degrees Celsius, the low pressure gauge should read between 50-55 psi, and the high pressure gauge should read between 275-300 psi.

      Thank you!

      -BDP

  12. I have a 95 F150. Just replaced fan clutch, compressor, accumulator, and orifice. Added appropriate amount of PAG oil, pulled vaccum, and charged 134a. Everything is cooling however at idle I’m seeing my pressure climb sky high before the fan clutch engages. So far example when the truck is warming up and the fan clutch is not engaged (several minutes), if I turn the AC the High side climbs to approx 350-400 (high side pressure sensor turns off compressor after 430 I believe), and the low side can get up to approx 60 – 70. Once the thermal fan clutch senses the high temperature it engages, the ac gauges read approx 35 low, 190 high. The truck is cooling great. Is this normal operation for a truck with thermal fan clutch. I read that the pressure should not be this high?

    1. Andy,

      Thanks for your question about your 1995 Ford F150. The fan clutch you installed responds to increases in temperature and the demand of the air conditioning takes a long time to get heat to the fan clutch to get it to engage so it is definitely possible that is normal operation for your truck. Most new vehicles have electric fans in addition to the engine driven fan that come on when the compressor is cycling. You might consider installing an auxiliary electric fan that comes on when you turn your air conditioning on to keep the pressures lower in your system.

      Thanks again for your question!
      -BD Auto Pro

      1. Thanks for the input! I’ve been looking into aux fans but also thinking maybe the fan clutch is no good even though it’s new. Basically I’m wondering if it’s just not spinning fast enough even when not fully engaged. I may have a shop take a look just to make sure. I did have another question, when I replaced everything, the ac sticker on the truck says max oil is 11 fl oz and to use WSH-M1C231-B? When searching online this appears to be a Ford ac oil that is equivalent to PAG 46. What’s interesting is that all online databases that show ac oil levels specify that 95 F-150 takes 7 fl oz (95 Bronco says 11 fl oz). This is confusing, as that is a big difference. I checked some other 95 F150s stickers that also said 11 fl oz. Anyways if my sticker is only stating max oil and not nominal level should i have put 7 ounces instead? Would this extra oil cause this issue? Once again, when the fan clutch kicks on pressures are normal. Thanks Again!

        1. Andy,

          Thanks again for your question about your F150. It’s possible your truck required a different amount of oil. The sticker is almost always correct but to be absolutely sure you can try calling your local Ford dealership and giving the service department your VIN and asking them to look up the amount and type of AC oil that your system requires. The extra oil in your system may reduce it’s cooling capacity and may eventually clog the dryer which could increase pressures, but if that was the case it would always the pressure would always be too high. It’s also possible that the fan clutch you received is faulty say it may be worth having a mechanic check that out.

          Thanks again for your question!
          -BD Auto Pro

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