Technical > Wiring & Sensors

A/C Support

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antonch:
I am looking at the DME pinout for my stock ECU that is going into the trashcan soon. It has:

* Input-A/C Pressure Switch
* Input-A/C compressor on
* Output-A/C compressor control
It seems that we can use MiscOut for A/C control. Most other standalones such as Autronic/AEM support this feature. Does VEMS?

rob@vems.co.uk:
Supporting A/C control is possible, and as it differs slightly across various cars we dont claim to support it out of the box, but its been possible on a few cars.

We can control the compressor on using a Misc Out channel, we just need to work out the function of the inputs.

With the Nissan I have two inputs - one is the Throttle pedal (which cuts the compressor on WOT) and the other is the A/C on button.

So we need to make a truth table up like this:
Pressure SwitchCompressor OnAC controlOffOffOffOffOnOffOnOffOffOnOnOn
And with a table like this all we'd need is an extra relay

antonch:

--- Quote from: rob@vems.co.uk on January 08, 2008, 09:13:23 am ---Supporting A/C control is possible, and as it differs slightly across various cars we dont claim to support it out of the box, but its been possible on a few cars.

We can control the compressor on using a Misc Out channel, we just need to work out the function of the inputs.

With the Nissan I have two inputs - one is the Throttle pedal (which cuts the compressor on WOT) and the other is the A/C on button.

So we need to make a truth table up like this:
Pressure SwitchCompressor OnAC controlOffOffOffOffOnOffOnOffOffOnOnOn
And with a table like this all we'd need is an extra relay

--- End quote ---
That table looks right to me. I am not sure if you need Throttle pedal input. Using MiscOut page we can just disable A/C at pressure > 100kpa and rpm > 3500 or so. I am not sure why you want to use relays. Can the ecu handle inputs?

rob@vems.co.uk:
That's right, the pedal input is going to be controlled by one of the MiscOut triggers.  And while the VEMS hardware can handle 3 inputs the software to control the A/C is not present, which is not really a problem as the solution looks a little like this:

Driver presses the A/C switch on the dash, the coil opens the circuit for the AC control which the VEMS handles based on your MiscOut settings.  The exact wiring depends on the dashboard switch - if it switches to ground when on then the relay coil will need a 12v supply not the ground connection.

The choice of which EC36 pin to use will be made based on the current drawn by the AC control circuit.

Bat:
Hi,
On the standard system I would expect the pressure switch to activate the cooling fans, is this not the case?
Cheers,
Gavin :)

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