Heating and Air Conditioning: Description and Operation

A/C Refrigerant System (R-134A), Pressure and Temperature Relationships

The pressures and temperatures in the A/C refrigerant system vary depending on engine speed (RPM), coolant fan speed 1 or 2, engine temperature, A/C compressor (ON/OFF), outside temperature, humidity, required cooling performance, etc.

Pressure and temperature specifications given in chart below are based on the following:
- Engine running for approx. 20 minutes
- Engine speed (RPM) 1500-2000
- Outside (ambient) temperature 20 °C (68 °F)

With the engine not running and ambient temperature at 20 °C (68 °F) the pressure in the system should he approx. 4.7 bar (68 psi).

To check pressures, pressure testing equipment must be connected to The service valve. See "A/C Refrigerant System (R-134A), Servicing". Service and Repair

A/C system with restrictor and accumulator, refrigerant flow





NOTES:
- Small arrows indicate the direction of refrigerant flow.
- Low side pressures are regulated and maintained within certain tolerances by the variable displacement compressor independent of engine speed (RPM). See refrigerant system pressure testing. Testing and Inspection

1 - A/C compressor, high pressure side
2 - A/C condenser
3 - Restrictor
4 - Evaporator
5 - Accumulator
6 - A/C compressor, low pressure side

Table of pressure and temperature relationships