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hi i have a c5 2002 2.0 hdi with manual temperature control with aircon. the aircon gives a high pitched whine when its going to work then about 30secs later starts blowing cold air for a few minutes then starts blowing warm air. it has got plenty of gas in the system i have checked it with a pressure gauge when the system has been on a long while about 1 hour the pressure reeds very high about double what it should be when cold pressure reeds ok. anyone got any ideas to help me??

many thanks

mark

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It is possible the amount of refrigerant gas may be low, even though the pressure may be ok. As a guess, the high pitched whine if from under the dash area, could be gas blowing through the pressure reducing valve instead of the more normal sound of liquid rushing through. If the gas is not being condensed at the front of the car (engine fan should be running to provide cooling and check the matrix is not blocked up) then only gas will be circulated and it will be heated up by the compressor and its pressure rise. Also worth checking when the pollen filter was last replaced in case it is restricting the air flow. The compressor clutch should be cutting in and out as the pressure goes up.

 

Any work on the system replacing bits that requires the gas to be removed/refilled has to be done with the right equipment to avoid any loss to the atmosphere, so you really have no choice but to go to such as a dealer for it checking/regassing. Cost for this was about £50 a couple of years ago at my dealer (our C5 air con was not cooling the air much at one side of the car, turned out to be low on gas. Car was 7 years old).

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The following guide is taken from the procedures for the latest C5 so may help a bit:

 

Interpretations of the pressures measured in the air conditioning circuit (Vehicle stationary, engine running)

High pressure / Low pressure // Symptoms / Possible causes / Solutions

 

- 8 to 10 bars / 3 bars

// Does not produce cold air / Excess oil in the loop OR Air or humidity in the loop / Discharge the refrigerant gas. Drain all of the oil from the circuit. Extract a vacuum in the circuit. Refill the circuit with gas.

 

- > 11 bars PRESSURE / > 4,2 bars

// The temperature of the intake pipe is lower than the temperature of the evaporator / Opening of the air conditioning pressure control valve too great / Replace the air conditioning pressure control valve.

// The high and low pressures become equal when the air conditioning compressor stops and these pressures fluctuate when the air conditioning compressor is operating / Intake or discharge valve jammed open by a particle or broken / Replace : The air-conditioning compressor

 

- Pressure lower than 7 bars / Pressure lower than 2,4 bars

// Does not produce cold air / Not enough refrigerant gas / Discharge the refrigerant gas, Test for leaks, Extract a vacuum, Refill the circuit with gas.

// The temperature of the intake pipe is lower than the temperature of the evaporator / Obstruction of the circuit on the low pressure side / Replace the pipe.

 

- > 11 bars / > 2,4 bars

// Fluid line (Filter drier iced up) / Obstruction of the fluid line / Replace the pipe.
// Filter drier iced up / Filter drier blocked /Replace the filter drier

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Worth checking that the flaps that set the temperature are still being correctly driven by the motors, and that the gears on same are not stripped. Search form for more info. This fault is usually one side or the other, but if you do not have split temperature control it could still be the issue. The chiller may not be getting any airflow across it....

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