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| The ratio for the period during which the signal is actually applied is indicated in display zone “3”. |
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| The operating and display unit, Climatronic control unit -J255- uses the ratio to calculate the pressure in the refrigerant circuit. The calculated pressure is indicated in display zone “4”. |
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| If the ratio is less than 12 % (corresponding to approx. 1.8 bar absolute pressure) and greater than 87.5% (corresponding to approx. 32 bar absolute pressure), the operating and display unit, Climatronic control unit -J255- does not switch on the compressor (the air conditioning system compressor regulating valve -N280- is not actuated). The compressor is only re-activated once the ratio exceeds 15 % (corresponding to absolute pressure of 2.6 bar) or drops below 48% (corresponding to absolute pressure of 16 bar). |
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| To prevent abrupt compressor shutoff on account of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the operating and display unit, Climatronic control unit -J255-: |
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| - As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) (full compressor output is not released again until pressure has dropped below 16 bar) |
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| - As soon as the coolant temperature exceeds 115° C (full shutdown at 118° C) |
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| Depending on the ratio, the operating and display unit, Climatronic control unit -J255- transmits a signal via the convenience data bus system to the relevant engine control unit, thus causing it to act on the radiator fan control unit -J293- to switch the radiator fan(s) -V7-. |
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| Depending on the version of the operating and display unit, Climatronic control unit -J255-, the radiator fan is either switched on immediately in air conditioning mode when the compressor is activated or the radiator fan is only actuated on exceeding a pressure of approx. 9 bar in the refrigerant circuit. |
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| At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from “-1” mark below “0”). |
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| The pressure in the refrigerant circuit and thus the ratio are governed by various factors. As a general rule, however, the pressure will not exceed 20 bar (absolute) with maximum compressor output and an ambient temperature of 20 to 25 °C. Under extreme usage conditions (e.g. in hot countries with high ambient temperatures, “stop and go traffic” and high relative humidity), the extremely high cooling output involved may also result in pressures of up to 30 bar (absolute). |
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| The high-pressure sender -G65- operates with a frequency of 50 Hz (50 Hertz = 50 activation pulses per second). The signal ratio indicates the proportion of the ON time per pulse. |
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| The activation signal can be checked for example using the vehicle diagnostic, testing and information system -VAS 5051A- (“Measurement” function) → Chapter (Checking signal from high-pressure sender -G65-). |
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| The signal generated by the high-pressure sender -G65- is also used to control the engine (the torque required to drive the compressor is governed by the pressure in the refrigerant circuit). Depending on the engine control unit version, the signal is displayed as signal ratio in the measured value block of the relevant engine control unit. |
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| The signal transmitted at a refrigerant circuit pressure of approx. 5 to 6 bar absolute corresponds to a signal ratio of approx. 22%, which is achieved with the compressor not running, at an ambient temperature of 20 °C and with the refrigerant circuit properly charged. |
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