How do you check a car’s AC refrigerant level?

How do you check a car’s AC refrigerant level? It’s been abnormally hot recently, and I’ve been using my car’s AC more, but the air coming out doesn’t feel as cold as it used to. I want to see if my refrigerant is low before going to a mechanic, as it could just be the heat getting to me.

Jack Walsh · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
Finding out your air conditioning isn’t working correctly is frustrating, and if you feel it might just be the heat getting to you, you’re smart to check the refrigerant level before visiting a mechanic.
To check the refrigerant, you will need:
  • Safety goggles
  • AC gauges
  • Thermometer
Once you have your supplies:
  • Inspect the air conditioning unit. If you discover any loose clamps or worn-out pieces, it’s time to visit the mechanic.
  • Attach the gauges to the low-pressure service port and the high-pressure service port. The low port is on the passenger side of the firewall between the accumulator and compressor. The high port is on the line between the condenser and the evaporator on the firewall. If you can’t find the ports, consult your owner’s manual.
  • Once attached, start your car and set the air conditioning to its coldest setting, using the recirculating air feature if available.
  • Place the thermometer in the center vent of your vehicle and allow the car to run for a few minutes.
  • Read the gauges once the pressures stabilize. The low port should read between 25psi and 45psi, and the high port should read between 250psi and 400psi. If both are low, you are likely low on refrigerant.
  • Read the thermometer and if it is 40°F or lower than the outside temperature, your air conditioning is working properly.
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