As the weather's been warming up recently ( ) I finally got round to using the Air Con on our 2006 3.6 TDV8 rather than opening the windows.
It wasn't doing much to cool the incoming air down - a bit cooler, but not a lot, so I thought I'd get the "top-up" can out with it's pressure guage to see if I had gas still.
Surprisingly, the gauge indicated I had plenty of pressure - possibly even too much at 55~65psi ??? Definitely nothing has leaked away. Reading was taken with the engine idling, but ambient in the high 20s (maybe 26 or 27C)

On my D2, the low pressure side runs somewhere between 30 ~ 40 psi & produces nice cold air.
I know the 3.6 uses a variable displacement pump rather than a fixed output as the D2, so I don't know what the low pressure should be. Should I expect to see similar values to the D2 & it's currently over pressurised OR is the higher value OK ?
If the higher value is OK, any ideas what could be causing the limited cooling ?
The AC compressor seems to be working & isn't making any unusual noises.

Some people on here have referred to getting AC low & high pressure values via their Gap IID diagnostic tool.
I tried that using mine, but couldn't get access to any live readings - Only the fact that their were no faults on the HVAC ECU.
Am I missing something on my iiD or is their a hidden menu somewhere ? Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 145,000 miles & climbing
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk

You won't get low side pressures from any diagnostics as there is only the high side sensor.
Pressures are, to a point, meaningless unless you know what your refrigerant charge weight is - I don't mean what the plate says, I mean how much is actually in the system. The only way to know this (and correct as necessary) is to recover, vac, and recharge.

Update & problem solved !
I drove the car again this morning with the AC on & again confirmed it's minimal performance. However, I heard the compressor whining when switched on (which I'd not noticed previously).
Past experience on my Disco 2 & other cars with Denso compressors has always suggested that the whining indicates low pressure, but not low enough to prevent the AC working. I've no ide why it gets noisier, but it seems consistent across 4 cars & 1 of them more than 5 times over 5 years !

Based on that & now that the ambient temperature has reduced back to "normal" I re-checked the low pressure side with the guage & realised I'd been stupid previously & not had the AC switched on - although the engine was running.
This time the pressure started at more than 75 psi then reduced to 25~30 psi when the AC was switched on. According to the gauge marking this was borderline too low - although I'm not sure of the basis of the markings. On Disco forums I've seen people quoting values just below 30psi as when the system will disengage (Although not seen in any workshop manual)
Past experience with the other cars has always suggested adding gas to 35~40 psi resolves the issue & fortunately this worked again. I've now got a quieter compressor & icy air from the ducts  Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 145,000 miles & climbing
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk

Pressure isnt the way to assess the gas content, it has to be done by weight. The pressures youre talking about seem way too low, all aircon units Ive dealy with are 160 psi and above. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

American, quite old but still relevant in terms of understanding pressure in airconditioning systems.
http://www.agcoauto.com/content/news/p2_articleid/257

I can't emphasise this bit enough

Quote:

What is static pressure in the system?
Before the vehicle is started, the static system pressure can be read. Pressure should be very nearly equal in both gauges. Actual pressure will depend on the type refrigerant and the ambient temperature and does not show if the system is properly charged.

Phoenix,

that article in the link is very informative - thanks.
Although it obviously stresses needing to know both low & high pressures to make sensible decisions & I accept the purist view that I've no idea of the volume of refrigerant in the system, I'm sure its not unreasonable to start with the assumption that the system was filled with the correct amount of refrigerant originally & that I'm probably suffering from minor leakage over the 4 years I've owned the car & the additional period prior to that since it was last filled.

The article does highlight that the low pressure values I was getting of 25~30psi with the system running are not unrealistic (article suggests approx 30 psi for a good system) & probably do indicate that my system was just slightly down on pressure / volume before a minor "top-up" corrected it.
My original value with the system off appears to be comparable with the quoted 90 psi "static" pressure quoted for a good system minus some leakage. My 55~65 psi value is very approximate as the gaugeon the top-up cartridge is small, the scale is non-linear & I'm sure not that accurate.
I didn't measure the static pressure after topping up, so obviously don't know what I've increased it to.

AJGalaxy,
from the article in the link, it's probably that the 160psi values that you've experienced are probably high pressure side values ? Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 145,000 miles & climbing
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk

How can you 'top up' a system without knowing the correct charge weight and the current charge? additionally, at best it's irresponsible to top up a known leaking system, it's also possible for a leaking system to draw in air (which is non-condensable) if the leak is on the low side or the high side if the restriction orifice (or on some vehicles, the thermostatic valve) is blocked, which will artificially increase the low side pressure.
Any aircon issue should start off with a recover, vacuum (and pressure leak test if the vacuum test fails or there is a leak suspected) followed by a recharge with the correct weight of refrigerant.
You may not like it because it will generally involve someone qualified to do it and therefore cost, but that is the only correct and responsible way to do it. If there is an issue after that, it's generally easy to diagnose as the refrigerant charge is known and pressure readings will be meaningful provided the ambient temperature is accurately measured.

Pawl wrote:

Phoenix,
AJGalaxy,
from the article in the link, it's probably that the 160psi values that you've experienced are probably high pressure side values ?

Advice please, running a TDV8 4.4 and suffering from the normal issue of AC not cutting in until after 5 mins and then intermittent working during running. Possibly the normal issue with PCV sticking. I took the car into my local garage today and explained to the receptionist when she asked what the problem was and told her I thought it was the PCV and that the AC cuts in after 5 mins.

Had to chase at 5.00pm and spoke to engineer, he said looks like compressor shagged as not engaging and working and there was only 20grm of gas in the system. I said I was surprised as it was recharged last month. I also was surprised as it was working lovely all day yesterday and on the way to the garage. I said about the PVC valve and he said I was confused as the control is within the cabin, I said no, it’s built into the compressor and is a known problem. He was unaware that this was a common issue on these units and then said it might just need valve replacing. I then found out that the receptionist had not passed on any of the information I had previously given.

Anyway he is going to get quotes for both replacement valve and price for new compressor.

I can understand from his point of view saying the compressor isn’t kicking in as he only run it for a couple mins.

What my question is, sorry for being long winded, but would the system work at all with only 20gr of gas ?

No it wouldn't work with a small charge of refrigerant in, how did they measure it though, did they evacuate the system to a recovery cylinder as that's the only way to measure it....

Allegedly they discharged it and measured it. They then said the recharged it and tested system and as it wasn’t working discharged and recharged again and concluded compressor shagged.

They may be confusing the RCV in the compressor with the Thermostatic valve on the bulkhead just before the pipework passes through to the cabin. These are known to be slow to react and can be the cause of 'slow starting' aircon (on any vehicle, not LR's especially) The system would not operate with only 20g of refrigerant in it, let alone give any cooling.

A problem with the RCV will not stop the compressor clutch engaging, low refrigerant pressure, an electrical / control fault or a faulty clutch itself will prevent the compressor from spinning, whether any pressure is generated or passes round the system is another question entirely...

Is the RCV the same as PCV that gets talked about on here. So am I correct in that a faulty PCV will still be linked to slow starting and intermittent operation. If I switch off and restart, getting fuel etc. it will take 5 mins again to kick in.

Probably, although the terminology is wrong, the refrigerant control valve controls the flow not pressure of liquid refrigerant.

I've just noticed a typo of mine regarding the Thermostatic valve, it is on the bulkhead just before the pipework passes through from the cabin, not to. It needs to be in the area of control, not outside of it.

Many thanks for your input. Much better informed for discussions tomorrow. So if the RCV not functioning correctly, no AC I presume.

Thanks again