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How to disable V90 air conditioning in winter?

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Old Dec 5th, 2018, 21:08   #31
Laird Scooby
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Do 960s/V90s have viscous fans? Pretty sure mine only has a Leccy one. Only heard it at full whack in the summer when it was 34*C!

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Leter 9xx cars had a two-speed electric fan under ECU control, earlier cars (possibly not 960) had a vicious fan and an electric one operated by a thermoswitch in the rad, or sometimes in the rad hose using an alloy adaptor tube.

As i've completely removed the vicious fan from my 760, i rely purely on the electric one that some previous owner has wired into the thermoswitch on the rad. Somewhere i have an alloy adaptor and (if memory serves) a Vauxhall Omega two-stage switch that switches at 92C and 104C so the 92C will bring a (yet to be fitted) primary fan on and if it ever gets hot enough or the A/C is running, the second (factory) electric fan will come on - project for another day though!
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Old Dec 5th, 2018, 21:16   #32
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Do 960s/V90s have viscous fans? Pretty sure mine only has a Leccy one.
See post #21.
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Old Dec 5th, 2018, 21:18   #33
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Dave,

On cars with fuel injection, ECU takes signal from A/C control unit (and in some cases also compressor clutch feed) and uses this to adjust Idle Air Control (IAC) valve.
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 .
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Old Dec 6th, 2018, 13:21   #34
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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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Old Dec 6th, 2018, 16:08   #35
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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 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,
Spot on - the engine ECU only has an INPUT from the ECC/MCC, it does not have an OUTPUT to the MCC/ECC.
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Old Dec 6th, 2018, 16:17   #36
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Spot on - the engine ECU only has an INPUT from the ECC/MCC, it does not have an OUTPUT to the MCC/ECC.
it's a long time since I investigated a 900 they never had AC problems ! However what I said does apply to the new generation cars starting with the 850 in 1992 .
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Old Dec 6th, 2018, 20:03   #37
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.....now averaging 44.3MPG over the last 20k miles (all long journeys, mostly with cruise control on at motorway speeds).
Well done Jim, that's impressive! Just goes to show what you can get out of a well looked after D24, contrary to the mutterings of others on here......
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