Since this is an air-conditioning refrigerant in newer automobiles, the optimal running pressure for R134A is between 22 and 57 pounds per square inch. As a refrigerant, a liquid capable of vaporizing at low temperature,that is used in automotive air conditioning, the U.S. Environmental Protection Agency, specifies that R134A is not flammable at ambient temperatures and equally not corrosive to metals such as aluminum, copper and stainless steel.
The Pressure Temperature Chart
Like any other refrigerant, the pressure of R134A rhymes with its temperature. You could determine the refrigerant pressure at any temperature between −22 and 202 degrees Fahrenheit by reading the value from a pressure temperature chart.
In a high-temperature refrigeration box, where temperatures ideally range from 45 to 60 degrees Fahrenheit, the coil temperature is, typically, between 10 and 20 degrees Fahrenheit colder than the box itself. This difference is simply referred to as the temperature difference.
The Normal Running Pressure
For the normal running pressure in an R134A system, the coil should function at 22 pounds per square inch at the lowest temperature, 45−20 = 25 degrees Fahrenheit. Thus, at the highest temperature, 60−20 = 40 degrees Fahrenheit, the coil should function at 57 psi. In other words, the normal running pressure of R134A range between 22 and 57 psi in that type of system.