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Home >> Audi >> 2007 >> A3 Base, Standard >> Repair and Diagnosis (Single Page) >> Heating, Ventilation & A/C (HVAC) >> HVAC Control Systems >> Air Conditioning >> 87 Air Conditioning >> Diagnosis And Testing >> Cooling Performance - With Manually Regulated A/C System, Checking >> Continuation Of Test: Pressure In Refrigerant Circuit Increases

Continuation Of Test: Pressure In Refrigerant Circuit Increases

-- Open hood.-- Repeat cooling performance test COOLING OUTPUT, CHECKING .
  • Is the coolant fan running during the cooling output test? The RPM depends on the coolant temperature and on the refrigerant circuit pressure, it is determined by the engine control module.
↓ Yes ↓ ↓ No ↓
-- Read the pressure in the refrigerant circuit and the radiator fan control using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
  • Do(es) Coolant Fan(s) run at increased speed when pressure in refrigerant circuit increases?
 -- Check the coolant fan activation using "output diagnostic test mode" using Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".-- Correct the coolant fan activation.-- Repeat cooling performance test COOLING OUTPUT, CHECKING .
↓ Yes ↓ ↓ No ↓  
-- Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel, refer to RADIATOR AND COOLANT FAN OVERVIEW and refer to A/C PRESSURE SWITCH -F129- and refer to A/C REFRIGERANT HIGH PRESSURE SWITCH -F23- . Bring the problems determined to the attention of the workshop. -- Check the coolant fan activation using "output diagnostic test mode" of Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".-- Correct the v activation.
NOTE:
  • The pressure in the refrigerant circuit depends on several factors. However, in general, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25 °C. Pressures up to 31 bar may occur due to extremely high performance under severe conditions (such as in southern countries with a hot climate, stop and go traffic and high humidity).
  • At temperatures below 25° C, the pressure in the refrigerant circuit generally does not rise above 16 bar (the coolant fans run and cool the condensers down).
  • Depending on the measured value, the A/C control module controls the A/C compressor regulator valve and tells the engine control module, via the data bus to control the coolant fan.
  • If the absolute pressure is less than 1.2 bar or greater than approximately 32 bar, then the A/C control module will not turn on the A/C compressor (the A/C compressor regulator valve is not controlled). The A/C compressor is switched on again only after the measured absolute pressure has become greater than 1.8 bar or less than 16 bar.
  • To prevent the A/C compressor from suddenly switching off because there is too much pressure in the in the refrigerant circuit or because the coolant temperature is too high, the A/C control module controls its power as soon as the refrigerant circuit pressure goes above 30 bar (absolute pressure) or the coolant temperature reaches 115 °C. Full A/C compressor output is released again after the pressure goes below 27 bar. If the coolant temperature goes above 115 °C, the A/C compressor output will continue to be controlled by the A/C control module. At 118 °C it is completely switched off.
  • If the refrigerant circuit pressure was greater than 32 bar, the A/C control module switches on the A/C compressor again only when the pressure has decreased below 29 bar.
  • Additional information regarding the pressure in the refrigerant circuit can be found in Vehicle Diagnosis, Testing and Information System VAS 5051 under "Guided Fault Finding".
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