Bush Pilot

I could use your input on this. My AC went from working great to not working at all, except for a case where it worked one time as before. Now it’s not working at all. Static pressure reads as it should for a full system at the ambient temperature measured in which indicates a fully charged system. Running pressures are no difference in static pressures.

I had the R-34a removed from the system and the shop said that the system was only half full of R-34a. I asked if we should try a refill to see if that was the cause and the tech said, “No. Even with a half full system, I should have seen a running pressure differential.”

My compressor clutch is engaging and I’m not hearing any bad compressor noises. I’m wondering if it may be worth trying to evacuate and refill the system before going down the path of replacing the drier/filter and compressor? A new OEM (Denso) compressor is about $400 with shipping. The cost to evacuate and refill the system is $100 + R-34a. The car is a 97 with 50k mi. so did a lot of sitting which is bad for a compressor. What would you do?

TexSquirrel

If it were me, I'd fill it and see if there is a pressure differential.
But I'm able to evacuate and refill myself, so the cost is MUCH less.

Are you certain the clutch was ever engaged?
If the pressure switch keeps the compressor from engaging, there wouldn't be a pressure differential.
If the compressor is replaced then you should replace the receiver drier, expansion valve, and condensers and flush the system before installing the new compressor.
All of that is required in order to have a warranty.
The only time I replace a compressor without doing all of that is when there is a faulty clutch and no aluminum is found when evacuating the refrigerant.
BTW, it's R134A.

Bush Pilot

Thank you for the correction on the refrigerant and response. When I command the compressor on, I hear the engine respond to the load so am assuming the compressor is coming on. Is that reasonable?

My understanding is that when the refrigerant is removed, only gas and a slight amount of oil that is in the form of a mist is removed. If that's true, how would you see aluminum in that process? Also, I'm guessing that the shop can measure the amount of refrigerant it took out by weight of the container before and after. Is that right?

My 97 Boxster holds 30 oz of refrigerant. Correct?

TexSquirrel

Yes, it's reasonable, but I like to watch the compressor and make certain the clutch is working properly.
I've seen really old clutches slip.

Refrigerant, oil and any aluminum shavings will be evacuated.
I watch the sight glass and can see if there's lots of aluminum being pulled.
Also once you disconnect the recovery machine, you'll find traces of aluminum on the connector.
You could weigh how much refrigerant you pull, but I never do.
I pull everything to a maximum vacuum as indicated by the gauges.
Then repair the system and pull a vacuum again for system testing.
Then I add the correct amount of refrigerant by weight.
During that process I inject the specified amount of oil.(Whichever oil is specified by the new compressor manufacture)

I could compare to my 996.2, but that might not be exact.(Although both systems are VERY similar, they're possibly not exact matches)
The best place to find out is the refrigerant specification label on the hood for the frunk.
I always use grams and not pounds.
My refrigerant scale is in grams, so it's what I'm used to.
If a label only has it in pounds or ounces(rare) I convert to grams.

Here's the 996.2 label:

Bush Pilot

My path forward now is to attempt to add the specified amount of R-134a and see what she does. If it's still not working it's only another $50 to have it removed again. Thanks for your help.

TexSquirrel

If you were closer, I'd evacuate it for you for free.
If you don't have a recycling machine, you have to send out your refrigerant to be recycled.
But it's not THAT expensive for 900 grams worth.
That's a drop in the bucket compared to how much is in a recovery tank.

Gasngo

Since I dont have a Boxster yet I just say can you see the compressor with the engine cover removed or is it down in the deep dark world of German gotcha American. TSquirl mentioned a few items like looking into the sight glass on the receiver drier where you can see refrigerant flowing. When the system is full the sight glass is clear and it ought to be blowing cold air. Also dont forget the Germans also run the refrigerant system in defrost. If its low you will see some movement or foamy maybe. If the compressor is not pumping then no movement there for clear. Now Ill assume you know this but Ill go over it anyways. The compressor pump drive consists of the belt pulley, electromagnet located under the pulley and the outer most part [hub / flange if you will ] connects to the inner working of the compressor and pumps the freon. When the clutch is engaged the magnet pulls the hub up against the belt pulley and make the inside spin. If you have the system on and you see the outer most piece spinning [hub] then its all online. If you have the system on but that hub is sitting still and the pulley is spinning away with the motor running of course then its not engaged and not pumping. If thats what you find then why? Low freon or no freon? Bad switch or sensor? Now if its engaged and you have bubbles in the sight glass its low. From there I would top it off and see what happens. The ECM and idle control dont know anymore than what they or it is told to do Ill assume thats what Porsche wanted . So if the idle bumps when you push the A/C or climate control it might automatically bump the RPM because of additional load even though the clutch is not engaged. So determine that your compressor is really engaged by watching the outer hub hook up to the pulley and spin while engine is running. Without the engine running and hot if you can reach the outer hub and spin it by hand it ought to have some resistance. If it spins super smooth then theres possibly something wrong but without me actually putting my hands on it all I can say is if everything is good Comp. wise you ought to be able to spin it with your hand or fingers what ever you can grab and it should take a little muscle to do it. If its sloppy or locked solid then you are on a different path. Hope this helps.

Also one word of caution refrigerant work can be dangerous know what you are doing.

TexSquirrel

I was actually referring to the sight glass on the attached gauges.

Also I would never add freon without a proper set of gauges.
The R134a cans available with 1 hose are not the best option because you can't see what the high side is doing.
My suggestion is use the correct tools, or don't do it at all.
Note: I have used the single gauge 1-hose cans before before I was trained in how to properly evacuate/repair/fill AC systems.
Now I no longer recommend them.
I have seen many systems damaged by people adding too much refrigerant.

Gasngo

Yep what he said. Again not owning one or being under the hood but if the drier does not have a sight glass then yep a good set of gauges do. Just verify the compressor is engaging or not. Start with the basics.

TexSquirrel

There isn't a sight glass on the 996 receiver drier.
I can only assume there isn't on the early Boxster also.
A good set of gauges can be purchased from Harbor Freight.
I use an old HF set and they have lasted longer than my previous tool truck brand.
I probably R&R about 5 or 6 complete AC systems per year and perform occasional refills as well.
(Mainly domestic & Asian, but occasionally European)

Bush Pilot

I evacuated the system and attempted to add R134a. With the compressor on the pressures hi and lo immediately went to about 25-30 psi and stayed there. It only accepted about 6 oz of R134a and then nothing was flowing in the sight glass. Would the refusal to accept refrigerant coupled with the same pressures hi and lo to indicate a bad compressor?

TexSquirrel

You'll need to have more than 6 ounces(170 grams) of refrigerant in order to get the compressor to kick on.
Most systems require close to 35 psi on the low side in order for the system to activate the compressor.
Did you pull a vacuum before refilling?
If not you'll have to start over.
You can fill both low and high side with some refrigerant while the engine is not running, but be certain to close the high side on the gauge before starting the engine and running the compressor.

Bush Pilot

Thank you. I did pull a vacuum on both high and low sides to around 29 mmHg for about .5 hr. So the recommendation is to try to inject some refrigerant into the high and low lines with the engine not running? My theory now is that the pressure in the can is the same as the pressure in the system, around 28 psi and if true, since everything is pressure equalized, no refrigerant is going to flow into the system regardless of what line I attach to or whether the engine is running or not. When I google this issue, compressor failed does come up as a fault mode. Thanks for all of your help.

Gasngo

Ill assume theres a fair amount of plumbing but I would expect 1 can to bring the Comp. online. That being said did you actually get your hands on the front hub and attempt to spin it by hand. Basic part of diagnosis. I would do that before any other time is spent with evac Etc.

Bush Pilot

I have now verified that the clutch on the compressor is not engaging when I command LO on the AC system from the cockpit. Apparently I was being fooled by the engine anticipating a load and responding to that.

How would I verify that the clutch is getting g the correct signal to engage?