Automotive Air Conditioning Information Forum

Hey all. Did a recovery and recharge on a buddy's 2006 Nissan 350z base model. It only took 0.4lbs from a deep vacuum and would not take any more. I found the gauges were equalized at about 70-90 psi, and the compressor clutch was spinning. Revving the engine only changed the pressure by 5-ish PSI. Condenser and blower fans feel strong. The compressor clutch's hub nut was tight as well. This car has a compressor with a variable displacement control valve, according to the factory service manual. The FSM also says to replace the compressor in this condition.

My question: Can the variable displacement valve, or TXV failure cause completely equalized pressures? Is there an easy way to inspect the valve when we take the compressor off, assuming the oil is clean?

I kind of think the compressor is shredded or broken internally, but I won't find out until this weekend when we recover it again and inspect the oil.

When the control valve fails nothing gets "shredded" - there will be no evidence in the oil.

I would question the inability to charge it properly first. Are you using cans or a tank?

Why was it recovered in the first place? How much refrigerant was recovered?

I was referring to the compressor internals shedding through the system, but was hoping a control valve stuck wide open could cause similar issues.

I'm using a 30lb cylinder and a digital refrigerant scale and a set of manifold gauges. It would only take 0.4lbs because the low side was not pulling down at all.

It was drained and refilled because he stated it was gradually cooling worse as the weeks went on. Those were typical symptoms for a leak so I suggested a drain, fill by weight, and leak check, then go from there. I don't know the amount since he had it recovered at a shop before he swung by.

System leaks slowly > Low charge causes poor performance > …

The problem is a stuck control valve can mimic all sorts of other issues. That is why the FSM says "replace compressor" - because it is not cost effective to do otherwise for a line mechanic.

You can't expect a compressor to "pull in" a charge. Especially a variable displacement unit.

Sometimes a proper charge will get a stuck valve moving again, it is worth a try.


With the engine stopped, and the system in vacuum - charge liquid refrigerant through the High Side port. Open the cylinder valve all the way, invert it for liquid and watch the scale. Spin the high side manifold valve open. Generally you can get 60% to 80% of a full charge in to a system in vacuum that way.


CLOSE THE HIGH SIDE VALVE, then start the engine.

You can finish charging vapor on the low side if the system begins working. If the system still offers no appreciable differential across the pump, then recover the system & replace the compressor.

I meant to post a reply to this but forgot. He took the compressor to the pro shop that did the evacuation and they said it was not moving anything at all and was completely worn out. We will be doing a compressor, and receiver drier this weekend. They oddly noted there weren't any metal shavings, so that leaves me a little baffled. Thoughts? Have you all ran into a completely dead compressor with no shed metal before?

No dice at all on the old compressor. Installed the new compressor and receiver drier today. Apparently you can do the receiver without removing the radiator or condenser. It's just kind of a pain in the ass. Took about 3 hours in total, including the vacuum. No apparent leaks.

Charged right up to 1.21lbs. Low side was in the 30-40 range.54f at an idle at the center-right vent, max blower, windows down, 90f day in the sunlight. My buddy is really happy with the job. The shop was gonna charge him close to $500 and I did it for $100. Had him hold onto the old compressor for spare clutch parts just in case.

Appreciate the feedback. Hopefully this post will help other Z owners in the future.