Clutch-Less Air Con compressor issues??

[harlie]

Hi guys, after some advice re AC

So my Octi FL (MK6 based) has AC issues – would seem Mk6 AC is no better than Mk5 which my bank account remembers well.

It has a Clutch-Less Variable Displacement AC Compressor and it is not operating at the low to medium capacity range. From what I understand, the HVAC ecu will ask the compressor to run at high to cool the car, once it is cool the compressor output will decrease to a level that keeps the car constantly cool. Same way an inverter system at home works except home systems are varied by compressor speed, where the car system is varied by changing the piston stroke length.

On a warm day it blows freezing air until the car cools down, then uncooled air (like the compressor has turned off completely) until the cabin temp starts to get uncomfortable, then freezing again ect ect. When it’s raining the windows and screens completely fog over after about 5-10mins – when the compressor drops out there’s no drying of cabin air. A window must be opened because it sometimes takes 10+minutes before the compressor kicks in again.

With 525g of R134A freshly inserted (we now don’t think it was low) the low side sat at 90psi with the needle fluctuating down to 85 every 3-4 seconds, like it was trying to start – or is this what we see normally as it needs to produce minimum 2% for lubrication??
The pressure starts to drop to 30-32psi within 30-40 seconds. I would class this as high output – top vent temp according to VCDS 6-7 degrees – thermometer agrees.

I can see the compressor load with VCDS and it ramps up as vent temp comes down which seems normal. However, when the car is started it does nothing for about 30-40sec. During this period the HVAC ecu could be sending a medium request??? Can anyone confirm what their compressor load does after starting?

So is it the PWM solenoid in the compressor (new compressor required), or the HVAC controller in the dash?? I’m not sure exactly which parameter is the request to the compressor – I’m sure it is a PWM signal so I would expect to see either a 1-12v or 2-100% -

any ideas please.

[hoi polloi]

When it’s raining the windows and screens completely fog over after about 5-10mins – when the compressor drops out there’s no drying of cabin air. A window must be opened because it sometimes takes 10+minutes before the compressor kicks in again....

Sounds like the same issue mine had..

VW fixed under goodwill.. New compressor, receiver dryer & regas.. The interweb seems to think it is the (refrigerant control??) valve on the compressor..

- Anthony

[harlie]

really? I received a new mechatronics under goodwill in July. Can I ask how old you car was at the time? Mine is a late 2009 with 62km.

And yes, after much reading and testing; it is the RCV (refrigerant control valve) in the back of the compressor. I’ve read that BIG thread on the other forum, carried out the tests described and can see the HVAC ecu asking for full AC with no action from the compressor for up to 10 minutes.

Dump from VCDS - compressor current at 0.820amp is considered as full AC output. As we can see by the compressor load, refrig pressure, vent and evap temps nothing is happening.


Address 08: Auto HVAC (3T0 907 044 AL)

20:19:31
005 Compressor current; actual value 0.825 A
006 Compressor current; specified value 0.820 A
007 Compressor load 2.7 Nm
040 Interior temperature 28.2 °C
042 Left front vent temperature 28.3 °C
078 Refrigerant pressure-MUX Kaeltemitteldruck 7.2 bar
116 Temperature after evaporator-MUX Temperatur nach Verdampfer 26.7 °C

What gets me is the valve can be landed here for $38, but the dealers and AC shop only want to replace the compressor, which of course means they want to replace the dryer bag (condenser has to be removed) and TX valve (half the interior has to be removed). The compressor manufacturer won’t give a warranty if the other parts aren’t replaced; sounds like an obvious money grab to replace a $38 valve.

[Umai Naa!!]

It will maintain the temperature you set it at.

So in other words, check all vent temperature sensors as well.

With regards to TX valves and receiver driers, unless the compressor has had an internal failure (not electrical), and you're planning on having the system open for any great length of time, I don't see a need to replace these. That is, if you're the one paying the bill

[harlie]

all vent temps were roughly the same unless I set the dials to 26 or higher, then the vent temp rose to 38-40 as it tried to heat. As you can see they are no colder than inside ambient - evap temp is the obvious one, it is on the evap an unaffected by the heater matrix. Once the compressor finally gets going the temps drop to 6-7.

No, mine does not maintain the temp I set it to.

I agree re drier and TX. the AC shop even says "they are not expensive parts so while we're there...." fails to mention the labour required.

I'm at odds with whether I take it to the dealer or get a valve in.

[hoi polloi]

really? I received a new mechatronics under goodwill in July. Can I ask how old you car was at the time? Mine is a late 2009 with 62km.

What gets me is the valve can be landed here for $38, but the dealers and AC shop only want to replace the compressor, which of course means they want to replace the dryer bag (condenser has to be removed) and TX valve (half the interior has to be removed). The compressor manufacturer won’t give a warranty if the other parts aren’t replaced; sounds like an obvious money grab to replace a $38 valve.

My car was about 8 months out of warranty (so 3yrs 8mths) and with just under 70,000km IIRC. I did the whole forum search thing and came to the conclusion the RCV was stuffed... There are two types though - one that is bolted on and one that is retained by a circlip (mine was the circlip one that seems to be the more common of the two). I went to the internet and bought one and in the meantime (while awaiting delivery) I thought I'd try VW and see what they said.. They didn't have any issue with fixing the whole lot under goodwill (which they said was $2500 worth of parts & labour)..

- Anthony.

[hoi polloi]

Harlie, PM sent...

[harlie]

Update:

Thank you hoi polloi!

New RCV fitted today.

Now as the compressor counts up to 0.820 the compressor load also counts up, and vent temp immediately counts down until it’s below 6deg. Adjust the temp dial and the compressor current varies down with the load and vent temp matching.

All the AC experts said I need a new compressor, drier and TX valve, now thinking back I bet our old mk5 only needed a valve when I paid 1500 for the 3 items...