D4 a/c not cooling

**BradC** · 21st November 2025, 09:12 PM

Originally Posted by scarry

Oh well,good luck to them,its the old story with anything mechanical,look after it and it will look after you.

When I was much younger I got a private tour of the WA Kwinana power station. The head engineer had worked for dad early in his career and was happy to give the ex-boss and his son a personal tour. He talked me through the shutdown and startup procedures for a generator and explained it was all about changing temperature slowly in order to look after all the metal. They even had auxilliary motors who's sole role was to keep the rotating mass slowly turning to prevent anything sagging. That was when I really learned about looking after machinery.

I've applied that across my life and it has served me well. Gentle warm ups, cool downs and maintenance. My son is picking up on that. Warm it up gently and let it cool down when you're done. Do the maintenance when it's due rather than when you think it might be needed.

I'm lucky enough to be able to be picky with my clients. Some of the buildings I work in I reckon you could safely eat off the plantroom floors.

**Graeme** · 21st November 2025, 09:53 PM

My son has discovered that the dryer is separate to the condenser even though 2012 Microcat doesn't show that it is on the D4 but does on the L322. This makes much more sense and should be much quicker and easier to change.

**DiscoJeffster** · 21st November 2025, 10:17 PM

Originally Posted by Graeme

My son has discovered that the dryer is separate to the condenser even though 2012 Microcat doesn't show that it is on the D4 but does on the L322. This makes much more sense and should be much quicker and easier to change.

Discovery 4 2010 - 2016 (l319) / Air Conditioning Condensr/compressr (3.0 V6 Diesel)((v)fromaa000001) | Jaguar Land Rover Classic Parts

**Graeme** · 22nd November 2025, 05:42 AM

Thanks.
There are lots of o/s suppliers but a Qld ebay seller has them. Furthermore a local proper a/c business might have one in stock a they fit lots of LRs and some Jeeps too.

**Graeme** · 22nd November 2025, 05:54 AM

A general a/c question - is the system pressure when at rest a vacuum? The D4 dryer sealing doesn't appear to expect high pressure.

**shack** · 22nd November 2025, 09:11 AM

The AC system pressure shuldn't be a vacuum.

When at rest it's normal for both the high side and the low side to be the same pressure, the differential occurs when the compressor starts pumping.

A problem than can occur on these is that if either the condenser or drier are blocked, the pressure on the high side can be much much higher than what the high low switch is reporting, this can lead to failure pretty quickly, and you'll never see the issue on the pressure switch.

My suggestion for anyone working on these AC's would be to just replace the condenser and drier together.

But I'm not an AC tech, however I have learnt a lot through failure!!

Mine and the car's.

**DiscoJeffster** · 22nd November 2025, 09:18 AM

Originally Posted by shack

The AC system pressure shuldn't be a vacuum.

When at rest it's normal for both the high side and the low side to be the same pressure, the differential occurs when the compressor starts pumping.

A problem than can occur on these is that if either the condenser or drier are blocked, the pressure on the high side can be much much higher than what the high low switch is reporting, this can lead to failure pretty quickly, and you'll never see the issue on the pressure switch.

My suggestion for anyone working on these AC's would be to just replace the condenser and drier together.

But I'm not an AC tech, however I have learnt a lot through failure!!

Mine and the car's.

Exactly. Hence when I’m fitting my new compressor I’ve also ordered a dryer and new condenser. I figure it’ll be more efficient than the old, worn one, plus I won’t need to flush it. Win win. Do it once (hopefully).

**scarry** · 23rd November 2025, 07:33 AM

Originally Posted by Graeme

The D4 dryer sealing doesn't appear to expect high pressure.

The drier is on the high pressure side of the sytem,similar pressure to condenser,while the system is operating.

**scarry** · 23rd November 2025, 08:04 AM

Originally Posted by BradC

I've applied that across my life and it has served me well. Gentle warm ups, cool downs and maintenance.

Exactly,i was thinking the other day,of all the vehicles we have had,over the years,including the business vehicles,which totals around 40,we have never had an engine issue,and very few other issues.Almost all the work vehicles did well over 300,000Km,before moving them on.Most had no repairs at all.
We serviced them ourselves,once out of warranty,but lately that has dropped off and some go elsewhere.
But we still keep a good eye on them and make sure everything is done properly,and on time.
We can't afford to have work vehicles off the road either.

**Graeme** · 23rd November 2025, 12:10 PM

Originally Posted by scarry

The drier is on the high pressure side of the sytem,similar pressure to condenser,while the system is operating.

Thanks Scarry.
I've just acquainted myself with a flow diagram - it's not what I prevously thought. However I don't understand how the low/input side of the compressor can be high and the high/output side can be low and that this is caused by a blockage in the system. Could someone please explain?

Edit: I just found this, so replacing the dryer is a logical 1st step. Presumably water vaporising causes excessive low side pressure.
With a faulty dryer, the moisture in the refrigerant would lead to lower pressure on the high side and higher pressure on the low side.

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