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
  • CarQuest Auto parts
  • NAPA Auto Parts
  • O’Reilly Auto Parts
  • Pep Boys
  • Fast Track
  • Bumper to Bumper Auto Parts Specialists
  • S&E Quick Lube Distributer
  • DYK Automotive
  • Fisher Auto Parts stores
  • Auto Plus Auto Parts stores
  • Hovis Auto & Truck Supply stores
  • Salvo Auto Parts
  • Advantage Auto Stores
  • Genuine Auto Parts stores
  • Bond Auto Parts stores
  • Tidewater Fleet Supply
  • Bumper to Bumper Auto Parts
  • Any Part Auto Parts
  • Consumer Auto Parts

Pictures Provided By:

ac_pressure.jpg – By Favor_of_God – Licensed by Getty Imagines – Original Link

Related Posts

8 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!


  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!!!

    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

Leave a Reply

Your email address will not be published. Required fields are marked *