Mine has a Sanden pump, I have replaced the G65 sensor and the system has pressure (later) VCDS shows the voltagge applied to the solenoid valve and the current drawn but no increase in pressure, this is also confimed by me testing it with a manometre set.

 

My MK1 ran withoiut fluid when I changed the pump but that had a clutch so was not turning, the Sanden pump runs continously and uses the solenoid valve for regulation, at the moment it will just be running withoit developing pressure but lubricated by the fluid.

 

I want to remove the valve, try to free it off or replace it but my concern is running the engine after depressurising the system as I believe that the refrigerant is a lubricant.

 

Or maybe I am worrying about nothing, by releasing the gas pressure the fluid will remain in the circuit as I will not be vacuuming it out?

 

Secondly I have a question concerning the pressure, the system was evacuated and refilled recently with supposedly the correct 525g but the guy (a friend) did not really knwo what he was doing so it may be less, the first replacement G65 sensor did not work, the second does and is showing 2.7bar on VCDS at todays 13°c temperature, does that sound correct as I expected more like 4 bar?

 

When I test with the manometre set, a cheap Chinese Ali-Express purchase it shows 4 bar on both circuits although its right at the bottom of the scale for the high pressure circuit where the G65 measures so maybe it is closer to the 4 bar, it does not rise when the AC is switched on hence my belief that the solenoid valve is inoperative.

 

I dont know whether to trust the 2nd pattern part G65 sensor or the guage set but in any case the control module believes there is enough pressure to energise the (I believe) non functioning solenoid valve.

 

Have little to do at this time of the year so want to tackle the job but it may be some while to find anyone here who wants to work before January to do the recharge and its possible that if I have to wait for a new sensor I could be driving a couple of weeks without system pressure.

The MK2 has a CVC compressor (Continue Variable Compressor) so yes, it runs continously. Even with the AC switched off, the compressor runs at approx 2% capacity.

 

Having refrigerant charge is mandatory. The oil in the compressor mixes with the refrigerant, so it will lubricate the compressor. No refrigerant = no lubrication, which might end up in burning the compressor. 

 

In a non-CVC compressor, the compressor often just 'locks up', causing the belt to pop or whatever (it stops turning so eventually the belt, which still tries to do its job heats up). In a CVC the same happens, but by design the connection beween the compressor between the pulley and the actual compressor is a less solid, so it will break internally (causing the pully to turn freely). This prevents further damage (belt and so on)

 

If you've run the system without refrigerant, that doesn't mean the compressor is always toast. However, you might have to clear the system, since there is a change of burned oil due to lack of lubrication. Contamination in the refrigerant is also bad for a compressor. You also have to refill the compressor oil.

 

You said the system was refilled recently with 525 gram. Usually, the do a discharge first. With this dischare they are able to see the amount of removed refrigerant and oil, so they know how much oil to add, and how much refrigerant was left. 

The amount of refrigerant left might be an indication of an actual leak, or just loss of refrigerant due to natural evaporation. Do you know these values?

 

Many garages just refill. Sometimes they include an UV dye to spot a leak (the leak will turn bright yellow when lit by a UV light). But based on EU regulations, this is actually not allowed. You're only allowed to refill a fully functional system.

If there is any leak, you're not supposed to refill and have to find the leak first.  However, this can take some time, so many garages just ignore this and refill (And charge both the AC and you) and ask you to return the next week/month. 

 

A good AC technican should charge the system with nitrogen and do pressure tests, and use the correct equipment to find the leak before refilling.

 

The MK2 has 2 'known issues' for the AC leaks: The condensor (its not very protected, so small stones and debris can hit the condensor easily) and the plastic nut at the condensor (This will eventually start to leak). 

Both requires replacing the condensor (approx 3-4 hour work). In wost case, the compressor needs to be replaced (another 250-300 GBP or so). 

I was lucky with only a replacement condensor (approx 60GBP) which took me 5 hours (I'm an IT guy, not a car mechanic)

 

First steps are

- Checking for refrigerant in the system

- Checking for proper operation of the pressure switch (this can prevent the compressor from starting)

 

You might consult a AC expert. Many garages aren't, they just recharge AC's and so on to have some additional profit, only a limited amount of them do have actual knowledge of refrigerant systems. Most just 'know which buttons to press'.

 

 

I have done all that you mention, pressure switch replaced and i know that the solenoid valve is stuck, system has 2.7 or 4 bar pressure dependant on whether you believe my AC guage set or VCDS (the difference might be that one is absolute pressure the other is guage pressure).

 

I know that there are no leaks because its held pressure and when it was refilled recently a vacuum was drawn and left for 20 minutes to test, almost as much regrigerant was withdrawn as was reintroduced but my pal was getting confused with units etc, trying to refill with 425kg so I'm not convinced that the correct amount was re-introduced.

 

I know that its pressurised be it 2.7 or 4 bar and that its enough for the system to function if the solenoid valve was working.

 

After my pressure test I released the pressure from the guage manifold (there are 1 way valves) and there was probably 5% liquid came out and 95% gas, on that basis if I vent the system very slowly with the guages up high I think most of the oil will remain in the pump which is the lowest part of the system.

 

I do need to have a carefull look to ensure that the shear plate or whatever the disconnect mechanism is is intact, it looked fine last time I looked but I do need to be 100% sure that the internals are turning.

 

My Sanden pump does not have the shear hub that the other make of compressor does, would anyone know what the failsafe mechanism is and if it can be seen?