D4 AC Intermittently Cold – Compressor Clutch Engaging, Recently Re-Gassed (MY13 SDV6

[tankwaste]

Hi all,
Looking for some advice on my MY13 Discovery 4 SDV6 air conditioning.


The issue:
The AC sometimes blows properly cold air, but lately it’s mostly just slightly cool rather than properly cold.


What I’ve checked so far:


System was recently re-gassed

Compressor clutch engages when I press the AC button


Clutch spins when AC is on, stops when off

No obvious warning messages on dash


No clear pattern related to driving vs idling (although I haven’t done controlled testing)



Other observations:


Air isn’t warm — just not properly cold

No unusual noises from compressor

Doesn’t seem to be rapidly cycling on/off

Cabin fan works normally

A few questions:


Could this point to the compressor control valve starting to fail (rather than full compressor failure)?

Would a weak control valve cause intermittent cooling like this?

Is it worth checking condenser fans / pressure readings next?

Could an HVAC sensor or ECU issue cause this without throwing any faults?

If it is the control valve, does the system need to be fully depressurised to replace it?



Trying to work out whether I’m looking at:


Control valve replacement

Full compressor replacement


Sensor/electrical issue

Something simple I’ve overlooked



Appreciate any guidance from those who’ve been down this road before.


Thanks in advance ?

[BradC]

When was it re-gassed? It's not unheard of for a service valve to leak after a re-gas. I've been caught with that twice over the years. Give it gas and it's all working great for a week or two, then it gradually drops off.

It could also be the control valve. Do you have a GAP? Have a look at the system pressure both at rest and while operating and report back.

[tankwaste]

When was it re-gassed? It's not unheard of for a service valve to leak after a re-gas. I've been caught with that twice over the years. Give it gas and it's all working great for a week or two, then it gradually drops off.

It could also be the control valve. Do you have a GAP? Have a look at the system pressure both at rest and while operating and report back.

Hey Brad,

It was re-gassed about 3 weeks ago, how would I check to see if it has a leak?

I don't have a GAP tool yet, trying to pick one up second hand. I have a cheap mongoose cable from AliExpress and the SDD tool it comes with but it seems to be pretty unreliable.

[BradC]

Unfortunately you need gauges really. If it's the compressor, the high side pressure will be low and the low side will be high. If it's short on gas the low side will be very low and the high side will be low.

I bought my Gap direct from Gap in Canada. I paid full price and it arrived in 4 days. It has been the best investment I ever made for the car. Keep looking, they come up pretty regularly (particularly from SDV6 owners when they snap a crank and move the wreck on). If you plan on keeping your car, they are absolutely a worthwhile investment.

For the A/C, unfortunately the Gap only shows what the car measures, and that's the high side. With either a gas leak or a stuffed compressor, the high side will be low, so that's not much of a help.

I'd take a 6 pack round to the local car A/C guy on Friday arvo and ask if he can put a set of gauges on and have a look for you.

[Blknight.aus]

it might also be the controls not stepping properly all the time, if the AC is on and the heater controls are open you get excellent demisting but suckful AC.

[Graeme]

Being so soon after the regassing, I would take it back to the person who regassed it who should put his gauges on to check pressures, which only takes a couple of minutes.

[tankwaste]

Being so soon after the regassing, I would take it back to the person who regassed it who should put his gauges on to check pressures, which only takes a couple of minutes.
Hey Graeme,
I had Raymond at Roverworks in Goulburn do the work on my D4 (I’m in Canberra, about an hour away). They weren’t licensed to carry out the A/C regas themselves, so they arranged for a qualified local technician in Goulburn to handle that part.
I’m hoping to avoid another trip down there just to have the pressure checked, if possible.

[Graeme]

I've always shied-away from A/C systems until very lately. I now have a set of ebay gauges that cost $76 which was cheaper than a single visit to a local mechaninc with gauges. I should have ventured into A/C years ago.

Edit: I'm further away from you than Goulburn though.

[DiscoJeffster]

I've always shied-away from A/C systems until very lately. I now have a set of ebay gauges that cost $76 which was cheaper than a single visit to a local mechaninc with gauges. I should have ventured into A/C years ago.

Edit: I'm further away from you than Goulburn though.

How’s that working out for you? [emoji38][emoji38][emoji38]

[Graeme]

Connecting the hoses is simple then open each valve at their line connections. No chance of getting the connections wrong because high and low vehicle connections are different sizes and the hoses and valves are colour-coded. I only wanted the gauges to see both sides, with no current intention of doing my own vacuuming and filling using HyChill.
I've just collected a little oil to use on o-rings when reconnecting after removing and hopefully cleaning the valve tomorrow by slowly draining off some gas into a clean container, although I'll collect all that I can during the discharge.

[BradC]

Before I bought a recovery machine, I had a gauge set and a rotary vacuum pump. Here's how I did a recovery.

I brazed up an adapter between the 1/4" SAE flare and a 3/8" LH gas bottle connector. I vacced the bottle out completely (Ok, I have a vacstat also, so down to > 200 microns). I bought a kilo of dry ice from BOC, put it in an Eski the gas bottle fitted in and topped it up with Metho. Dropped the gas bottle in which chilled the gas bottle to ~-80C. Hook up the gauges, vac out the whole assembly. I had a ball valve on the end of the vac hose. Then connected the vac hose to the "very cold" bottle and opened all the valves. That sucked all the gas out of the system and into the bottle. _all_ of it.

I could weigh the bottle before and after which gave me the refrigerant weight +/- 1g (I have $40 35kg shop scales that are both accurate and calibrated).

To get the gas back in, hook the stuff up, vac out the system and gauges, connect it to the bottle and turn the bottle upside down. Open the high side valve and let it suck as much liquid in as it can. When it has stopped, shut the high side valve, start the vehicle and slowly bleed the remainder into the low side using the low side valve. Close the coupler on the high side and open the high side valve on the manifold. Bleed everything back into the low side until the pressures equalize. Then you can close the low side coupler and disconnect.

A _lot_ of dry ice is much cheaper than a credible recovery machine. Most recovery machines have orings that struggle with hydrocarbons, so it's a much more cost effective way to do it. I bought a cheap Chinese recovery machine (still $800), sealed the electrics, replaced all the seals with viton and am good to go. I could buy a lot of dry ice for that.

[scarry]

That sucked all the gas out of the system and into the bottle. _all_ of it.

.

And for those that don't do these types of things often,just be carefull,as your lines,and the system,and the gas bottle can get into a vacuum.

The less air and moisture into any system the better,even if it is going to be evacuated later.
Any air in the with the reclaimed refrigerant in the gas bottle means the refrigerant cannot be reused.


One of our $2.5K recovery units got a gut full of water through it the other day,not ideal.[bigsad][bigsad]

[BradC]

And for those that don't do these types of things often,just be carefull,as your lines,and the system,and the gas bottle can get into a vacuum.

This is a hugely valid warning. ^^^^ <---- read that.

If you do it my way with Dry Ice, they _will_ get into a vacuum. If you do it the way I described, the only possible moisture entry point is the short bit of pipe between the bottle valve and the ball valve on the hose. If you use a 4 hose manifold (separate vacuum hose) then even that isn't an issue. Either way, a new dryer will take care of that.

Hydrofluorocarbons (HFCs) are bastards of refrigerants, and because they are **** refrigerants they need **** oil to lubricate. Their **** oil will often hydrolyze with a bit of moisture and turn to acid, dissolving your lines and compressor. Using Hydrocarbons and decent oil will mitigate this, but none of these cars come from the factory with this refrigerant or oil.