D4 a/c not cooling

**Graeme** · 16th November 2025, 05:35 PM

My old D4 had a new genuine Denso a/c compressor fitted with the engine swap. The vehicle isn't being driven. Some time after the a/c was gassed with Hychil, the a/c was found to not be cooling at all but then worked very well as soon as a climate control fault was cleared, with the fault possibly caused by an earlier totally flat battery. Now a couple of weeks later, the a/c again doesn't cool.
Static pressure of around 89 psi rises to around 103 psi with the engine running. The pipes are basically ambient temperature and the evaporator temperature several degrees higher. The clutch is engaging when the a/c is switched-on. No faults are recorded. Being a new compressor, the assumption is that the flow control valve in the compressor should be OK. The connector for that valve is inaccessible so the effect of unplugging that connector can't be determined. Unplugging the pressure sensor connector causes several faults and when refitted and the faults cleared, the faults don't return. The battery was disconnected for 30 seconds to force a restart of the climate control ecu, but without any change.

Does anyone have suggestions of possible causes or tests to try please?

**BradC** · 16th November 2025, 06:05 PM

103 PSI is close enough to ambient at the moment. Have you put gauges on it? What is the low and high side? Unless they are close, I'd be inclined to look for a leak. Either the compressor isn't compressing or there's bugger all there to compress.

I did a recharge on our D3 just after we got it, which turned up a leaky service valve.

**Graeme** · 16th November 2025, 07:13 PM

Thanks for replying.
We don't have gauges. My understanding from the WSM is that the pressure indicates adequate refridgerant but we may have to get the pressure checked. There are no pressure faults, low or high.

We're confident that the compressor isn't pumping anything worthwhile but not being able to check the signal to the valve we can't tell if the compressor is or isn't being instructed to be at minimum displacement. That the system worked well some 2 weeks ago when last started, many months since the system was regassed, suggests that the fault is electrical/electronic rather than lack of refridgerant.

The 2 calibrations have been done and all the controls appear to work so I'm wondering if something such as WOT condition is met, which suspends a/c operation.

Does anyone know if the LR diagnostic tool can monitor the signal to the compressor control valve? The IIDtool doesn't have such an option.

**scarry** · 16th November 2025, 07:19 PM

If the compressor is definitely turning over and keeps operating,at those pressures,it maybe not pumping.

Are the High and low side pressures the same when the compressor is operating?.

Edit,Sorry Graeme,didn't see your post above.

**BradC** · 16th November 2025, 07:20 PM

Originally Posted by Graeme

Thanks for replying.
We don't have gauges. My understanding from the WSM is that the pressure indicates adequate refridgerant but we may have to get the pressure checked.

Not really. Refrigerant pressure is a P/T relationship between liquid and gas. There can be 2/10ths of **** all liquid, but as long is there is *some* the pressures at rest will be the same. So the D3 needs ~550g of refrigerant. If there was 100g of liquid the pressures would be the same at the same temperatures (at rest). If the compressor was running however there'd be not much on the high side and the low side would be in vacuum.

While it's nice the car gives a high side pressure, without a low side pressure you're a bit in the dark. Whacking a set of gauges on you should be seeing ~>200 psi high side and ~50psi low side. (Ambient +20-30c on the high side and ~4-6c low side).

**Graeme** · 16th November 2025, 07:46 PM

Thanks Brad for the education.

The 3.0 D4 2-zone WSM specs state 600g of R134A.

**BradC** · 16th November 2025, 09:06 PM

Graeme, I'd take it to anyone who does vehicle A/C and get them to put a set of gauges on. This is one of those things that need a bit of extra help/equipment to diagnose.

If it has a good charge and a buggered compressor you'll see not much pressure differential. If you see a good compressor and bugger all charge you'll see a massive difference. Either way, looking at the high side you might see the same thing. You really need to get a look at the differential pressure to have more of an idea.

Where the bloody hell is 4bee? He'd be all across this.

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