Thread: D4 AirCon issues

Originally Posted by Graeme

My understanding of the sticky valve fault is that the a/c is slow to start but keeps going thereafter. If this the case then maybe your system is just low on gas.

Possibly. I was about to say it was only a couple of years ago I had the valve changed and regas, and then I checked the records 11/2019, so that’s four years ago!

Great idea, regas it is.

Originally Posted by Graeme

My understanding of the sticky valve fault is that the a/c is slow to start but keeps going thereafter. If this the case then maybe your system is just low on gas.

I'm pretty sure the fault with ours was the RCV, but the end result was really random performance, it would come and go off at will. Sometimes a bumpy road helped.

Originally Posted by scarry

What a wonderfull set up

Yep, crap indeed.

The only thing I may add to possible safety features is that there is a pressure switch/sensor, and the operation of the RCV in this scenario.

One possible way to diagnose RCV vs gas level is that when the AC is turned on, the ECM will add extra fuel to it's inject routines to compensate for the extra load created by the compressor.

If the gas is low, this doesn't seem to happen, if the gas level is ok and the RCV has failed to the "destroke" position, the engine idle speed will increase as the compensation fuel is still added, with the expectation that the RCV "commanded position" has been attained, and therefore we have extra load.

If the gas is low but the system has integrity, I'm guessing the the RCV would be commanded to minimum, which should hopefully save the compressor.

If the system is breached, you get the grey death..... And a repair bill that's more than the value of the car.

As always, I await my orders to ascend to the top of Mt. correction.....

Cheers

Originally Posted by shack

If the gas is low, this doesn't seem to happen, if the gas level is ok and the RCV has failed to the "destroke" position, the engine idle speed will increase as the compensation fuel is still added, with the expectation that the RCV "commanded position" has been attained, and therefore we have extra load.

It's not a case of "add extra fuel resulting in a higher idle". The HVAC ECU monitors the evap temperature. If the temperature isn't dropping fast enough (or at all) it asks the ECM to idle up a notch. This then happens a second time. So if it's low on gas and not cooling then you'll wind up idling at 1000RPM as it tries to add extra cooling.

Same effect as you indicate but the mechanism isn't different. It's not adding fuel to cope with the load of the compressor, it's giving the ECU a higher target RPM.

Originally Posted by BradC

It's not a case of "add extra fuel resulting in a higher idle". The HVAC ECU monitors the evap temperature. If the temperature isn't dropping fast enough (or at all) it asks the ECM to idle up a notch. This then happens a second time. So if it's low on gas and not cooling then you'll wind up idling at 1000RPM as it tries to add extra cooling.

Same effect as you indicate but the mechanism isn't different. It's not adding fuel to cope with the load of the compressor, it's giving the ECU a higher target RPM.

Thanks, I'll walk up the mountain a little way...

All things considered, I think I'll stop commenting on D3 D4 AC issues.

Obviously above my pay grade!

Originally Posted by shack

All things considered, I think I'll stop commenting on D3 D4 AC issues.

Obviously above my pay grade!

Don't stop, everyone's input is very enlightening (or terrifying) for a 300Tdi Defender owner 🥺

Tony

Originally Posted by shack

All things considered, I think I'll stop commenting on D3 D4 AC issues.

Obviously above my pay grade!

I don't think it's above your paygrade, some others maybe.