MkV air conditioner load

[Greg Roles]

Hey all,

I have been working on an electronic way to cycle the air conditioner compressor on and off under high throttle applications. I've read that Porsche amongst others turn their compressors off under WOT until about 3000rpm and decided this might be a good thing for laggy diesels. I'm at the point of hooking up my Jaycar controller but I recently read on here somewhere that the compressor is continually variable from 2% up to 100%. Thus I have to ask the question: does anyone know if the VW compressor already reduces it's load under WOT? I've already noticed the air output varies from time to time and this would tie in with the continuously variable nature of the compressor, but I'd love to know for sure before I mess with it!

[chrisgti]

I think my old falcon did it.. well it sounded like it did.

[isaw]

our old vs commo did it. you could see the light go off on anything over 3/4 throttle

[Transporter]

Hey all,

I have been working on an electronic way to cycle the air conditioner compressor on and off under high throttle applications. I've read that Porsche amongst others turn their compressors off under WOT until about 3000rpm and decided this might be a good thing for laggy diesels. I'm at the point of hooking up my Jaycar controller but I recently read on here somewhere that the compressor is continually variable from 2% up to 100%. Thus I have to ask the question: does anyone know if the VW compressor already reduces it's load under WOT? I've already noticed the air output varies from time to time and this would tie in with the continuously variable nature of the compressor, but I'd love to know for sure before I mess with it!

Hey, Greg
You could use VCDS to find out.

[wokwn]

Yes our compressors are variable displacement types, 2 - 100%

I think when the 'requested torque' figure heads towards 100% or available torque the aircon is backed off anyway, but I can't remember where I read that.

Anyway, there is no electric clutch you can release to cut off the compressor.. The displacement control is by a rattle valve and controlled by a PWM signal from the HVAC controller.

HVAC diagnostic channel 11.3 shows the PWM output between 0 and 200 (so divide by 2 to get the compressor output percentage). Maybe you could watch that channel during hard acceleration to see what happens.

[Maverick]

I've already noticed the air output varies from time to time and this would tie in with the continuously variable nature of the compressor, but I'd love to know for sure before I mess with it!

Why would the air output have anything to do with the compressors operation?

The air output is controlled by a blower inside the car and the compressor is pumping refrigerant around.

[Greg Roles]

As in air temp rather than velocity.

[Greg Roles]

OK, thanks to the clever suggestion to map the load using Vag Com, I can confirm that the MKV air compressor does indeed decrease it's load on acceleration. I found a channel with the actual NM load of the air compressor. For the record, adjusting the fan made no appreciable difference to this value. With the AC on, at 22 degrees at idle the load hovered around 5nm, and putting the temp on low raised the load to just above 6nm. On standing start WOT acceleration the load drops to about 1nm regardless of temp setting, and the load averages about 3nm on normal driving. Seems to be highest at idle.

What was really clever is if you try rolling acceleration off boost, that is below 1800rpm or in any "lag" zone, the load drops to zero. It seems any time you really overload the engine the compressor load vanishes, to return once on boost. Nice one VW!

No AC controller necessary for me, I think I can live with losing 1nm, or just switching it off to get zero load. Obviously this measurement is the compressor reading itself, and there must be *some* actual parasitic loss all the time through the compressor, generator and belt, but I'm happy the compressor is adjusting itself with the throttle application.