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Summary of change:
Air Conditioning subpage of GenBoard/UnderDevelopment/FirmWare GenBoard/VerThree firmware * can provide enable / disable signal for AC (eg. provide ground for clutch relay), via misc outputs * can sense 0/5V AC-On signal (take care not 12V ! Apply through a diode, so diode anode goes in to a pulled-up mcp3208 analog pin.). Any changes can be applied through TableSwitch : ** higher iac_reference position/pwm values ** changed iac_PID parameters ** and other changes (lower redline maybe) '''Things below are mostly outside the scope of ECU''' - they are controlled by simple sensors (widely available in the AC industry) and relays. ---- '''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. * Often the compressor clutch is engaged in defrost mode (even in cold temps) - Reason is to reduce cabin humidity to help eliminate fogging more quickly. Probably not something we should do, but worth mentioning. ---- 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) ---- '''Vasilis' suggestion''' i think i have a solution for a very stable idle control for the audi engines that can have a good solution for the A/C function as well, and can make it work with the IAC valve+diode Here is what is needed: Under idle settings, put a dialog, IF A/C turns ON, then decreace Idle PW by X number. If you cannot control the AC function through VEMS, ( i mean when it comes ON or OFF) then you can actually do this by using battery voltage: SO if Vbatt = 13.00 then IAC PW decrease by X number so you can make a simple table of 5 values (i dont think more are needed) so that the IAC PW can change depending on Vbatt. This can work in combination to the IAC PW/ CLT. So for example when CLT=80 and IAC PW=20 if vBatt=14.00 BUT if CLT=80 and vBatt = 13.40 (just when the fan kicks in) then IAC PW=18 etc. That way you can possibly eliminate the problem with idle drop AND use the IAC succesfully. We '''actually do that since 1.1.4x : apply higher IAC PWM duty with lower VBATT voltage. (It's done automatically, unconfigurable atm).
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