JPS

So I'm reading through the air con diagnosis threads here.

I've diagnosed and replaced a faulty footwell motor. I've diagnosed and ordered the fresh air motor (should arrive today).

I measured the pressure with the cheap replacement can kit gauge, and it shows (on the low side) it is a little high, even when running. I think it was running 25 at the lowest, 40 at the high, and going up into the red when off (hoping that's normal?).

So it seems I need to let a little out. Short of going into a shop and all that, is there a simple way to take a little out?

Thanks,

TMc993

You really need to pull a vacuum on the system, then refill it with the proper amount of refrigerant. Anything else is just hit-or-miss.

wwest

Perfectly, PERFECTLY, normal readings.

Low side will be lower with compressor clutch engaged, getting, growing higher during compressor off cycle. System off for long enough for the high/low side to equalize, >70 PSI will be normal.

therossinator

Did you take the ambient temperature into account?

JPS

It wasn't much more than about 75F out at the time. So if I read this correctly:
https://rennlist.com/forums/993-foru...diagnosis.html
it should have been 9 lbs and 16lbs , not 25 and 40. Even at 100F+, according to that link, 19 lbs would be the high cycle of the low pressure.

So it seems to me I have too much schtuff in there, no?

Seems I should start the car, warm it up, turn on the air, ensure the pressure really is in the 25-40 range as it cycles on/off, and if so, either take it someplace to suck some out, or perhaps suck up the minor environmental hit and let some out a little at a time until the pressure is ambient adjusted to something more appropriate. No?

This is of course after replacing my fresh air servo as well.

NOTE: I did reread the link and see that I didn't have the car at 2000 RPMs. I had it at idle. Not 100% sure what that will do to the pressures so I guess I have to get a helper and find out.

willus

The 2000 RPM's does matter. It is surprisingly tricky (at least on my car) to get the engine to remain steady at 2000 RPM. I used a spare 2x8 jammed between the accelerator pedal and driver seat rail to set the RPMs (other adjustable length "assistants" are probably better). To get to 2000 RPM, the best approach I found was to slowly creep up on 2000RPM from below -- once I went over 2000 RPM, I pretty much had to go back to idle and slowly start ramping-up again.

wwest

Most systems will disable the compressor to prevent damage if the high side pressure falls below about 30 PSI. So ~30 PSI will be the minimum pressure you see with the compressor running full bore, flat out. Obviously that pressure will rise during the compressor off cycle, off long enough, full equalization, >70 PSI would not be unusual.

TMc993

+1....I had exactly the same experience. I was at a non-Porsche AC shop run by a friend. We were attempting to follow the Porsche procedure but the 2000 RPM thing was a pain. My buddy thought I was exaggerating the difficulty of holding 2000 RPM, but when he tried it, he was worse than I was. We finally were able to hold it long enough the get a stable reading, but it took more time than it should have.

JPS

I was referring to the low side. I don't have an AC manifold set.

wwest

Sorry.. If the high side falls below the point at which the compressor circuit is disabled you can be CERTAIN/SURE that the low side is equal or less.