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Summary of change:
'''Air Conditioning clutch output ... subpage of GenBoard/UnderDevelopment/FirmWare''' Many ECUs control Air Conditioning (AC) clutch output. Currently there is no firware feature for AC in GenBoard/VerThree, but it seems fairly simple. MembersPage/MarcellGal is not an AC expert, but studied his air-conditioning system (can post scanned schematic, but it's nothing more than described below, with some hardly readible Italian abbreviations). ---- '''Air Conditioning clutch output:''' Clutch active when signal +12V. appr 450mA (26 Ohm) * '''relay''' is the natural choice * '''stepper output''' would work too * standard low-side power-output (eg. a spare injector channel) would not work, unless with a relay. ---- '''Air Conditioning clutch output activation rules''' * AC system pressure is 200 .. 2500 kPa * cabin fan on (eg. switched in 1..4 position, not in 0) * not agressive acceleration (optional) * engine running for a few seconds at least (optional) ---- '''Main fan activation rule''' * AC system pressure > 1700 kPa * or CLT temp > threshold (eg. 97C) ... note: histeresys * the main fan can usually be powered through a (big) series resistor under certain conditions (for light fan-RPM). Although, unknown (to me) condition. ** The only reason I have ever heard given for 2 speed fan is noise. Generally however, with AC on, fans run at high speed. Note that the main fan usually draws 30..40A - almost always a relay is used and a 50A fuse. The main fan is the 2nd biggest current eater (after the starter motor). ---- '''Input signals''' '''AC system pressure signal''' * AC system pressure within 200..2500 kPa range (active-low) signal * AC system pressure > 1700 kPa Naturally, a single pressure sensor can be used instead of the above range switches (eg. an MPX700A). '''Other signals''' * AC enable switch * AC control dials (warm/cold/temp) * headlight switch * CLT temp * ... ---- '''Misc stuff''' These might surprise the unaware, when debugging an AC system: * the AC "snow-symbol" is dimmed when the headlights are on * when the warm/cold dial is in most cold position (sensed by a end-position-switchbutton), a pneumatic valve (using intake manifold vacuum) activates a bypass valve that makes the coolant go around the cabin-heater. This way heat from the coolant will not sneak into the cabin, even if the air-valve "flap" is not perfect. What happens during long duration WOT when there is no significant vacuum ? Will the bypass operate correctly ? I don't know * the ECM is notified about the (AC controller intention of) AC clutch and the main fan, so the iac valve can be opened in time, and RPM target raised * Compressor clutch is usually disengaged (not powered) when in WOT. ---- Some systems are certainly different to some degree. '''Automatic AC systems''' have somewhat more parts, eg. * temp sensor * and control of warm/cold mixing (electro-pneumatic or electric actuation)
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