Clutchless AC compressor lubrication when not running

[JHZR2]

My 2008 ML320 diesel had a fine running ac system. I didn’t use it for a few months and now the AC isn’t coming on.

In the past it had occasionally been sluggish to start, but then it would run perfect.

The compressor has 206k miles. Static charge is perfect. I checked with gauges. This is one of those clutchless compressors which has a Denso variable actuator on it.

Our 2008 VW rabbit had the same type compressor.my wife complained of sluggush AC. We had a shop evacuate it, replace the valve on the compressor, and then recharge and it was perfect after. That may be the case here, as I don’t know that there’s any good reason to replace the compressor.

But I don’t know when I’ll do it. And I may want to drive the vehicle a bit. Thus the question:

A standard clutched compressor would just command the clutch off (or cut the belt in the old days!),and there were no worries. These new ones are always moving. There’s a wash plate and some variable flow valve.

Using my scantily I’ve seen it commanded to 100% with AC on (not cooling of course), and down to 32-49% when HVAC is on but AC button is turned off, and 0% when HVAC is off completely.

Of course I don’t want to damage, or worse, seize up the compressor and throw the serpentine belt. I’m not sure if that’s really a thing. But I’d hate to find out the hard way on the highway.

Are these clutchless compressors lubricated differently? Do they have their own reservoir of oil that isn’t reliant on refrigerant flow?

Or, is it that the solenoid can’t possibly go to full closed (0%), even if the hvac is off and it is commanded that way? So essentially a minimal amount of flow has to go through, even if it isnt producing a refrigeration cycle?

Just don’t want to drive it and do damage.

Thanks!

 

[JavierH19]

They rest cracked open so they don't produce vacuum in them and still let some oil pass in. Pretty much all modern ac compressors on vehicles no longer have a sump and pickup tube.

Those really old Mercedes compressors were like that and were thus incredibly hard to kill since they didn't depend on refrigerant bringing oil back to the compressor. The oil stayed there though it can eventually get pumped out into the condenser but it was designed to stay trapped.

As for clutch ac compressors they're both original on my 298k and 344k gmc's and i haven't even shimmed them yet. If an ac clutch is well designed and manufactured i see no reason why it wouldn't last a half million miles and the variable thing in the clutchless compressors usually fails sooner than a simple non variable clutched compressor.

 

[RooflessVW]

As I understand it, no freon flow = no lubrication. It should always bypass a little so I don't see harm in driving it with the aim of repairing it.

If you ignore it, you'll eventually lunch the compressor but you don't seem the type.

 

[JHZR2]

As I understand it, no freon flow = no lubrication. It should always bypass a little so I don't see harm in driving it with the aim of repairing it.

If you ignore it, you'll eventually lunch the compressor but you don't seem the type.

I don’t think I could ignore it terribly long because I like my AC!!

 

[shortyb]

I have one of those compressors in my 2010 VW Passat (continually running, variable displacement). From my understanding the oil remains in the entire system as the electronic control valve that adjusts the swashplate angle does not close completely, even when demand is low/off. This allows the oil to still lubricate the compressor pistons and seals as refrigerant flows through the entire system

This compressor doesn't have a reservoir per se, but still holds 50-60% of the total oil capacity. So if I were to replace just the compressor, I would have to ensure that amount is in the compressor when installed. If you replace the entire compressor, dump out the oil and measure it, then replace with the same amount of fresh PAG oil. If just replacing the control valve, I don't believe any extra oil has to be introduced other than lubricating the seals on the valve.