Compressor Issue?

[rocket rod]

Recently I changed all struts and all worked well at this stage. Just noticed now at starting the car my compressor runs for a few seconds, stops, then runs a few seconds again etc, etc and after while settles down. it's a D4 MY 2016 with 175K. This is a new issue, what could be the problem? Compressor or ride height sensors or other? Car levels correctly.

[loanrangie]

Drier desiccant starting to break down possibly, no dash messages or error codes ?

[rocket rod]

Drier desiccant starting to break down possibly, no dash messages or error codes ?
no codes and it's a Hitachi compressor

[BradC]

Recently I changed all struts and all worked well at this stage. Just noticed now at starting the car my compressor runs for a few seconds, stops, then runs a few seconds again etc, etc and after while settles down.

This is for a late D3, but all the info I've seen indicates the D4 is similar but maybe with slightly different pressures :

If you have no leaks and don't drop height it should run once every start*, and twice every couple of starts* (2-3 in my experience).

* Where a "start" is after the vehicle being stopped and idle for some indeterminate amount of time I've not been able to accurately pin down (>5 mins and less than an hour).

After months of observation the algorithm "appears" to work like this.
Start car.
Pressurise gallery from reservoir to measure pressure (open reservoir valve, wait until pressure stabilises and close reservoir valve). Note if pressure is above ~16.(5-7) bar absolute.
Vent gallery to ~2bar.
Start compressor and wait until gallery > ~10bar. Stop compressor
Vent gallery to ~2bar.

If initial pressure measurement was < 16.(5-7) bar then :
Start compressor
Open reservoir valve and wait until gallery > 17.7 bar absolute
Stop compressor
Close reservoir valve
Vent gallery to ~2bar.

2 or 3 pressure tests is enough to drop the reservoir below the 16.x threshold and make it pump up. It runs every start and pumps the gallery up > 10 bar as a compressor test.

If I run into the shops, generally it doesn't re-do the test on a warm start.

[loanrangie]

no codes and it's a Hitachi compressor

Are you sure its a hitachi ?, all D4's from 2012 ish should be AMK.

[rocket rod]

Are you sure its a hitachi ?, all D4's from 2012 ish should be AMK. Looked at compressor type in the GP tool and it said it was Hitachi. That's all I was going on. Haven't had a look though.

[scarry]

This is for a late D3, but all the info I've seen indicates the D4 is similar but maybe with slightly different pressures :

If you have no leaks and don't drop height it should run once every start*, and twice every couple of starts* (2-3 in my experience).

* Where a "start" is after the vehicle being stopped and idle for some indeterminate amount of time I've not been able to accurately pin down (>5 mins and less than an hour).

After months of observation the algorithm "appears" to work like this.
Start car.
Pressurise gallery from reservoir to measure pressure (open reservoir valve, wait until pressure stabilises and close reservoir valve). Note if pressure is above ~16.(5-7) bar absolute.
Vent gallery to ~2bar.
Start compressor and wait until gallery > ~10bar. Stop compressor
Vent gallery to ~2bar.

If initial pressure measurement was < 16.(5-7) bar then :
Start compressor
Open reservoir valve and wait until gallery > 17.7 bar absolute
Stop compressor
Close reservoir valve
Vent gallery to ~2bar.

2 or 3 pressure tests is enough to drop the reservoir below the 16.x threshold and make it pump up. It runs every start and pumps the gallery up > 10 bar as a compressor test.

If I run into the shops, generally it doesn't re-do the test on a warm start.

That is how my my12 D4 behaved,but I don’t know what pressures it cycled at.

[PTCAAR]

I have a MY 07 Disco 3 with Hitachi compressor and it does the same thing on start up. Exhausting then running the compressor, then exhausting and running the compressor. I never noticed it until I changed my compressor and removed the sound deadening in the compressor housing. I thought it was a fault with the compressor. Seems like a crazy function to drop the air and run the compressor on every start up all that needless work the compressor performs.

[BradC]

I have a MY 07 Disco 3 with Hitachi compressor and it does the same thing on start up. Exhausting then running the compressor, then exhausting and running the compressor. I never noticed it until I changed my compressor and removed the sound deadening in the compressor housing. I thought it was a fault with the compressor. Seems like a crazy function to drop the air and run the compressor on every start up all that needless work the compressor performs.

Depends on your point of view I suppose. Is it better for the car to tell you “sorry there is a problem with the suspension” when you leave the driveway, or would you rather find out when you beach it and it can’t extend?

[PTCAAR]

Depends on your point of view I suppose. Is it better for the car to tell you “sorry there is a problem with the suspension” when you leave the driveway, or would you rather find out when you beach it and it can’t extend?
I hadn't thought of it that way, thanks for the different perspective. [smilebigeye]

[BradC]

If you read the sequence I posted, I didn't really explain why it does each item.

First pressurize gallery and vent is to measure the pressure in the reservoir.

Run compressor and vent is a compressor function test (which is why it only pumps up to about 10 bar absolute and not the 17.7 bar threshold).

If the measurement in the first one was under the threshold it then starts the compressor and pumps the reservoir up. That's the second compressor run and third vent.

If the reservoir, pipework and center valve block is in good order, the second compressor run shouldn't happen each startup. It takes 2 or 3 measurement cycles to lose enough air to put the reservoir below the threshold.

The early software on the D3 didn't vent the reservoir after use and they found it was shortening the compressor life having it start up into a serious head pressure, which is why the revised software vents the gallery any time it's above 5 bar absolute and idle.

If you get the reservoir valve leak like I did, on a long trip it will slowly leak the reservoir into the gallery, the gallery will then exceed 5 bar and it'll vent. This will happen some 10 times and then the system will fault with the "too many cycles" error. On mine at that time it meant driving for more than ~2 hours 45 minutes without stopping (which I could never do with kids in the car).

[veebs]

Looked at compressor type in the GP tool and it said it was Hitachi. That's all I was going on. Haven't had a look though.

I’d have a look, as the logic for the AMK and Hitachi are different. I believe the AMK runs a lower pressure, which might explain why, if trying to achieve Hitachi values, it is running different to expected.

[BradC]

I’d have a look, as the logic for the AMK and Hitachi are different. I believe the AMK runs a lower pressure, which might explain why, if trying to achieve Hitachi values, it is running different to expected.

Also the Hitachi has 2 temp sensors (head and brush pack) and the AMK only has one (head).