Yes that's correct, I ran the HF 3 cfm pump for several hrs, than close off the manifold valves leaving the hose ends open to monitor pressure / vaccum.
Both low and hi side show -0 and will hold 24 hrs, so I then charge, purging can hose before opening manifold valves.
Then I open the low side, Freon flows and gauge registers, gets enough in that compressor will run when eng started.
Blows cold, in green on ac thermometer.
Next day, no ac

Edit: at 80 deg, low side = 35/40, hi side = 175/200

 

I know that you said -0, but there's a range. Does it move at all?
Get a sniffer, HF sells one for ~$60 and other members in your part of the world may have one. It may not be the compressor so it's money well spent.

 

ok, sniffer it is, and yes -0, the needles are pegged at the stop, well at least the hi is pegged at the low stop, the low reads -0

 

The low side gauge should go past 0 to 30 inches of vacuum... If it only goes to 0, you won't be able to tell how much vacuum you are pulling as 0 is actually atmospheric rest pressure. If the gauge goes past 0 and when you are running the pump the low-side gauge stays at 0, you are not pulling a vacuum at all, but are sucking air in from the leak. Can you post a pic of your low-side gauge?

Dan
'91 928GT S/C 475hp/460lb.ft

 

Can't post pic from phone, but it is -1, the lowest reading on the low side showing on the red scale.
So yes, it is pulling a vaccum on both sides, hi and low.
Thanks for confirming, I followed a video on YouTube

 

I've driven my car in your Texas heat and humidity, still plenty cold. It's been in 110º+ Cali central and west San Fernando valley heat and still plenty cold. Inland Empire area here with over 100ºF and still cycling on the freeze switch. With that jumpered (the usual configuratiuon here on the coastal desert plain) , it still pulls down to less than 25º. It's never obviously tripped the high-pressure switch contacts. The ability of R-134a to get cold has never been an issue. For most folks, keeping the condenser pressure under control at high ambient temps is the challenge. The fans --must-- work correctly, with a clean condenser and no airflow restrictions like leaves and crud between the condenser and the radiator.

 

Very good.

 

I read that when converting the system you should rebuild the hard line. How do you do this and is it necessary?

 

How does one go-about replacing the hoses with barrier hose?
Source for hose? Do you re-use the 928 hose fittings?

 

Any recommendations on an inexpensive sniffer that does the job? HF was mentioned, is anyone using one, if so how did it work?

Thanks,

Dave

 

No, the hard lines are not rebuilt, just flushed.

Dan
'91 928GT S/C 475hp/460lb.ft

 

There are three ways to go:

1) Try and reuse the 928 fittings. The downside here is that the fittings have barbed ends and most barrier hose is not designed for barbs, so that may or may not work.
2) Use standard fitting replacements. Of course the fit is not 100% same as stock with these. Aftermarket kits use these with good success
3) Hack off the ends off the 928 fittings and weld on beadlock fittings. This would be the best of both worlds, but requires more work

I have personally reused the stock 928 fittings with barbs using barrier hose in the past and they held up fine for years. The barbs on the 928 fittings I had were pretty shallow, and as long as the fittings are not over-crimped and you use good quality barrier hose, they should be fine. If you want to do this yourself, you will need an A/C crimper such as this one. You can buy barrier hose like this. On the 928, high side is #8 and low side is usually #12, but I have seen some earlier cars with #10. The third small hose connecting from the condenser to the hard-line that goes to the expansion valve is #6. Be careful, there is standard and reduced diameter hoses and the 928 uses only standard.

Dan
'91 928GT S/C 475hp/460lb.ft

 

From what I've been reading on Sniffers they are not the way to go to find most AC leaks.

Using them under the hood with fans and engine running is iffy at best due to air movement. Also if the tip touches oil it gets contaminated, so you'd want one with a replaceable tip. Sound like they are only good for interior work.

Most AC guys are recommending the dye w/ glasses?

 

When using a sniffer, the engine should not be running. On a charged system, the rest pressure on both sides is 80psi or above, more than adequate to find a leak. In your case, since you are losing a complete charge in one day, the leak is so large you should be able to hear hissing if you get close enough to the leak.

Dan
'91 928GT S/C 475hp/460lb.ft

 

Many thanks for the advice, Dan.