Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...
Air conditioner with refrigerant R134a - Edition 11.2018
3.9
Tests and measurements performed
with pressure gauge
Pressure gauge scales
1 - Temperature scale for refrigerant R134a CF3– CH2F or
CH2F– CF3
2 - Pressure scale
Note
Pressure can be measured in various units: 1 MPa (megapascal)
is equivalent to 10 bar gauge pressure, or 145 psi; 1 bar absolute
pressure is the same as 0 bar gauge pressure, which is roughly
equivalent to atmospheric pressure.
Pressure gauges may have one or more temperature scales in
addition to the pressure scale. The scale values for R134a are
assigned according to the vapour pressure table. As different re‐
frigerants develop different vapour pressures at the same tem‐
perature, there is a temperature scale for each refrigerant.
⇒ “3.9.1 Tests and measurements which can be performed using
pressure gauges”, page 70
3.9.1
Tests and measurements which can be
performed using pressure gauges
Refrigerant circuit pressure and temperature measurements
♦ The high-pressure gauge measures the pressure and tem‐
perature propagated evenly from the air conditioner compres‐
sor outlet via the condenser to the constriction (restrictor or
expansion valve) when the air conditioning system is switched
on.
♦ The low-pressure gauge measures the pressure and temper‐
ature propagated evenly from the constriction (restrictor or
expansion valve) via the evaporator to the inlet of the air con‐
ditioner compressor when the air conditioning system is
switched on.
Note
The relationship between pressure and temperature indicated on
the pressure gauges only applies in a refrigerant circuit containing
liquid or vapour, but not gas. In gaseous form, the temperature is
approx. 10 °C to 30 °C higher than the pressure gauge reading.
Detection of refrigerant in a closed vessel
In a closed vessel or in the refrigerant circuit, refrigerant R134a
is present if the temperature indicated on the pressure gauge
corresponds to the temperature of the refrigerant (standing liquid
assumes ambient temperature).
A closed vessel or a deactivated refrigerant circuit is empty if the
temperature indicated on the pressure gauge is below the tem‐
perature of the refrigerant.
70
Rep. gr.87 - Air conditioning system
English 
