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Suggestion · Original poster
Finally the workshop manual is a bit confusing says test AC cooling temp @ center console vents with motor at 2000 rpm.
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Recently need an AC recharge on my '03 996 4s. Had it since last summer when on hottest days I thought AC could be working better on 90F days. Used one of the simple recharge cans of 134a with gauge. Followed the directions ( AC on full, car idling etc) but never got to requisite PSI for the ambient temp in the instructions. In fact only got to about 25 from initial of 20 psi. It was a big can so I figured the cheap gauge was wrong. Concerned I got a set of Hi/Low AC gauges that read 32-35 psi on low side and 200-245 Hi side at 80F. I get ~45F at the vents so its colder than before.
Here's my confusion. I just found the Porsche 996 workshop manual AC charts. Converting Bar to PSI puts low side range (non temp dependent) @ 20-25 psi and high side 195-275 psi @ ~80F. So it appears I'm overfilled.
But there's a lot of misinformation out there....even Pelican parts puts low side @ 25-45 PSI and so does my cheapo can with gauge. Looks like potential for a lot of overfilled AC units.
Finally the workshop manual is a bit confusing says test AC cooling temp @ center console vents with motor at 2000 rpm. This is the last mention of RPM before showing the Hi/Lo charts on next page.
My question is does 2000 rpm also apply to reading the Hi/Low gauges or are they done at idle? Any long term downside for the slight overfill I have?
Your current numbers seem correct. If u google r134 pressure charts u will see the pressure ranges for every 5* increase in temp. Many things can effect the numbers too like moisture in the drier or debris in the system causing a restriction.
There are a lot of variables when dealing with A/C pressures. The A/C pressures are only reliable
if
you know that you have the correct amount of refrigerant in the system, anything else is guess work. That's why all A/C shops have gone to recovery/recharge systems. The refrigerant is removed/recovered and measured/weighted ( that's how you tell how much was in the system) , then the proper amount is charged. Then the pressures can be used to evaluate/diagnose the system.
IF you are concerned you have overfilled it, you can go to a shop that has a recovery/recharge system, they can recover the refrigerant and tell you if you overcharged it, then refill to correct amount. Yes, they will keep any "leftover" refrigerant and still charge you..
+1
I have learned that there is a very narrow band for optimal operation. I used to think that being over filled by a few ounces wouldn't affect performance, and was actually a good thing, as performance would be maintained as refrigerant is lost over time. Being over filled actually hurts performance.
On a side note, empirical data from some experienced mechanics indicates most auto AC systems lose about an ounce per year of refrigerant. I assume it is mostly past the compressor shaft seal with a little lost past fittings and other tiny leaks.
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