Measuring pressure and temperature in a "switched-on" refrigerant system
WARNING: This page does not describe the selected car, but rather 27 other vehicles, including the 2002 Volkswagen Cabrio, 2001 Volkswagen Cabrio, 2000 Volkswagen Cabrio, 1999 Volkswagen Jetta, and 1999 Volkswagen Golf. However, it is still accessible from the selected car via links, so may be relevant.
Use the A/C refrigerant high -pressure gauge to measure high pressure between the compressor and restrictor (including condenser) with the A/C switched on.
Use the A/C refrigerant low-pressure gauge to measure low pressure between the expansion valve and the compressor inlet (including evaporator) with the A/C switched on.
The temperature displays of the low - and high - pressure gauges apply only to a portion of the low - and high -pressure sides. The low -pressure gauge displays approximate temperature between the expansion valve and evaporator outlet. The high -pressure gauge displays approximate temperature between the compressor outlet and restrictor.
NOTE:
The temperature/pressure relationship only holds true when the refrigerant system contains liquid and vapor, but not when it contains only gas. In the gaseous state, the temperature is approx. 10 - 30 °C (18-54 °F) higher than indicated on the pressure gauge.