What Should My Car AC Pressure Be?

Car AC Pressure, Car AC pressure gauges Your car ac pressure can tell you almost everything you need to know about your air conditioning system.  If you are a do-it-yourself type of person even a little bit you’ve probably had some experience with the AC recharge cans that have a built-in pressure gauge that you can get at your local auto parts stores or online.  This gauge can tell you a little bit about what is going on in your air conditioning system, but it’s really only half the picture.

Car AC Pressure: High-side and Low-Side

These gauges that come with a small can of refrigerant are showing you the low-side pressure in your system, or the pressure right before the compressor.  To get a full picture of what’s going on in your system you also need to measure the high side pressure. The low-side pressure gauges are easy to find because they measure relatively low pressure so they don’t need to be super accurate and they are inexpensive to build.  The high-side pressure in your system is hundreds of PSI higher than the low side so it requires a different connection and more advanced gauge.

To measure the high side pressure in your system you need an AC gauge set.  These gauge sets come with a gauge for the low-side and high-side pressures, as well as a line to connect your system to a refill can, and often times a sight glass so you can observe the condition of your refrigerant.

Having the right tools is a huge step in the right direction, but now you need to know what the indications you’re seeing really mean.  Unfortunately, your air conditioning system doesn’t have a set level that means everything is ok like your engine oil dipstick. There is a range of high-side and low-side pressures that are acceptable and they change depending on what the ambient temperature is.  Your AC gauge set should have come with a list of pressures that are acceptable or you can use this chart.

If your pressures are in range everything should be working normally!  If not, check your ventilation system for proper operation or check for a clogged condenser or expansion valve.  If you find low pressures on both sides of the system then you probably need to add refrigerant. Similarly, if you find high pressures on both sides of the system you may have added too much refrigerant.  A low pressure rise from low to high-side usually indicates a failed compressor while a higher than usually high side pressure indicates a clog somewhere in the system.

If you find a low pressure on both sides then you’ve probably got a leak.  To seal your leak and get your system working again use Red Angel AC Stop Leak to quickly seal your leak and add a small amount of refrigerant.

If you had a large leak and your system is completely empty you should have your system evacuated and refilled as that is the only way to be sure you’ve got the correct amount of refrigerant.
Red Angel AC Stop Leak & Conditioner







You can pick up BlueDevil AC Refrigerant Stop leak at one of your local 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 Distributor
  • 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:

car_ac_pressure.jpg – By Saravuth-photohut

2 responses to “What Should My Car AC Pressure Be?

  1. Pressures were both low(20-150), added refrigerant and pressures are within range(40/45-225). The clutch is engaged, appears the ventilation door works, fan is blowing hot air. Had a bad heater control valve, replaced with a 1/4 turn valve. Has two fans on condenser and they are both working. Not sure what else to do? Thanks

    1. Shawn,

      Thanks for your question about your air conditioning. If your pressures are where they should be and you’re sure your heater control valve is working allowing all the air to bypass the heater core then usually it means you’ve got a problem with your expansion valve. The expansion valve is where the pressure drops and the refrigerant should get cold but if there is a problem with the valve or the pressure is dropping too slowly there it won’t cause the cooling effect in the refrigerant.

      Thanks again for your question!
      -BD Auto Pro

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