Idea to improve economy of aircon

[mickthemaverick]

Having had my aircon working properly now since the overhaul I have noticed two main characteristics of using it:
1) Fuel consumption goes up significantly
2) Power away from the lights is reduced.

I now automatically turn off the aircon when stationary or approaching junctions and hills to give me max power if needed. That means I use less fuel at the times of heavier throttle and have the benefit of the power. I notice that the cooling effect is not really altered during these periods due I believe to residual pressure in the system.
So I am wondering if it is possible to turn the compressor on and off according to the throttle position sensor and thus run the compressor mainly when using gravity or momentum as the driving force on the belt. I think I would say that any more than 25% throttle turns off the compressor giving all power to the car when needed. So 1) could it be done in software, maybe by using the TPS output to replicate the condenser pressure sensor's output and thus turn off the compressor as required?
and 2) what do others think of the idea?

[white exec]

I'm guessing the AC compressor will already be cycling in and out (ECU operated clutch) according to need to cool, and the need for extra engine cooling when coolant is running very hot.
Would have hoped the 2.2HDi had more than enough oomph to cope with the AC ?

When I've switched AC on mid-acceleration* (on several PSA cars, petrol and diesel), I've never noticed any fall-off in available power.

* Not a good habit, as it asks compressor clutch to engage at speed; better to do it at idle, or foot-off, according to many mechanics.

[myglaren]

Perhaps I am not as well attuned to my heaps as you are but I have never been aware of any lack of power while the aircon was running. Not that it does any more to test it. And the fuel consumption has always been crap anyway.

[mickthemaverick]

I'm guessing the AC compressor will already be cycling in and out (ECU operated clutch) according to need to cool, and the need for extra engine cooling when coolant is running very hot.
Would have hoped the 2.2HDi had more than enough oomph to cope with the AC ?

When I've switched AC on mid-acceleration* (on several PSA cars, petrol and diesel), I've never noticed any fall-off in available power.

* Not a good habit, as it asks compressor clutch to engage at speed; better to do it at idle, or foot-off, according to many mechanics.

My car has allegedly been rechipped to give 60mpg and 170BHP. The power is there once the turbo comes in but there is a significant dose of turbo lag made worse when the aircon is on. Hence my routine for uphills etc. I drive with very light throttle most of the time so maybe I need to buy some lead boots

[white exec]

Have to wonder about the quality of the rechipping.

Good rechipping usually involves an improvement in throttle and turbo response, and an available increase in both power and torque. Given that, it's possible to drive a turbo-diesel more sympathetically (less need for welly) and so obtain an improvement in mpg.

'Leaning off' - by reducing available fuelling - can do the opposite. Sounds a bit like that for yours.
Is it a chipbox that you can simply disconnect (or adjust), as an experiment?

[GiveMeABreak]

I'm guessing the AC compressor will already be cycling in and out (ECU operated clutch) according to need to cool, and the need for extra engine cooling when coolant is running very hot.
Would have hoped the 2.2HDi had more than enough oomph to cope with the AC ?

When I've switched AC on mid-acceleration* (on several PSA cars, petrol and diesel), I've never noticed any fall-off in available power.

* Not a good habit, as it asks compressor clutch to engage at speed; better to do it at idle, or foot-off, according to many mechanics.

Spot on Chris - the A/C compressor is already being switched in and out as needed and is controlled by one or more ECUs as obviously pressure has to be closely monitored and maintained.

[Gibbo2286]

Air con is said to add approximately 8% to fuel consumption, it's also said that you get the same effect by driving with the windows down due to loss of streamlining.

[mickthemaverick]

Is it a chipbox that you can simply disconnect (or adjust), as an experiment?

The car was advertised as chipped by a company in Newquay. I have contacted them and they have no record of chipping carried out before 2009 so I honestly don't know if it has been done or not. I am getting around 600 miles to a tank of normal driving and it does have more go than my last 2.2 but I think the job is more of a remapping of the existing ECU than an additional chip box. Unless I take it down to Cornwall I cannot really say what it is. Maybe I'll have to do that next time I visit my Son in Plymouth. I may rig a mini camera on the aircon clutch and display on the screen so I can see when it is in or out and go from there!!