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Old Dec 6th, 2018, 13:21   #34
Rversteeg
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Last Online: Today 13:18
Join Date: Feb 2006
Location: Amersfoort (NL)
Default Ecu

Quote:
Originally Posted by Clan View Post
yes , The Engine ECU actually controls the AC . The command comes in to it from the climate unit to request cooling , if conditions are right the engine ECU will activate the AC clutch , ambient and engine temperature and engine RPM , AC Pressure are a few of the factors which enable the request to be allowed to pull the clutch in . So if the AC does not turn on when you press the button there are a lot of checks needed to find out why .
I am not quite sure that this is correct. The AC compressor clutch is fed in series with a low pressure switch and a high pressure switch. The power comes from an auxiliary relay. In case of an MCC system it is integrated in the printed circuit board inside the MCC panel. In case of an ECC system it is a seperate component. When I switch on the AC on my MCC system, I can hear the relay in the panel clicking once. The actual switching on and off of the compressor is done by the pressure switches. The ECU only gets a signal that the AC is engaged to prepare the idle speed control system for the additional load. It also does something to the cooling fan control, but I never noticed any differences.
On MCC systems and ECC systems of the last series B230FK/FT the electric diagrams show no feedback from the ECU to the MCC/ECC panel, so at least for these models the ECU cannot actively influence the AC.
Btw, on an MCC system it is sometimes necessary to resolder the auxiliary relay on the printed circuit board.
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