Ducman82

greg told me to let it run for an hour or 2. close the vac pump line and let it sit overnight to see if the needles drop, indicating a leak

Rob Edwards

I finally got around to buying a short adapter hose so I can run my micron gauge in line with my Robinair pump- Next time I have a car to evacuate I will collect some data on how deep a vacuum it'll generate, how fast.

Bilal928S4

What I have found is that when you shut off the pump, it has to be disconnected from the gauges, otherwise the hose to the gauge will get filled with the vacuum pump oil. Even if the gauges are closed, the hose is still under a negative and will suck the vacuum pump oil up.

Rob Edwards

My Robinair has a lever that switches between the vacuum hose connection and atmospheric so you can 'break' the vacuum to the pump before turning it off, without affecting vacuum in the hoses. Or you could just close the valves on the gauges and loosen the connecting hose at the pump inlet before turning it off.

The Robinair pump (#15600) was $202 on Ebay a few years back. Incrementally more than the HF 2-stage, but built like a tank.

dr bob

And of course a reminder that the 'holds vacuum' test is a looky for BIG mistakes. The fittings on the car are o-ring sealed, so vacuum actually draws things together tighter, often sealing small leaks in the process. If you are seriously looking for leaks, pressurize with dry nitrogen and start the search with soapy water at every connection, looking for bubbles. Then evacuate overnight and charge just until pressure is a bit positive relative to atmosphere, search again with electronic sniffer. If still no leaks, add the rest of the charge and sniff/soap spray again. If still no leaks it's OK to start the engine and drive.

Kevin in Atlanta

Which is why I liked the GAST - it does pressurization as well. It was instrumental in finding a gross leak on my 87. I know it is not nitrogen , but it was sufficient.

bureau13

Tell me more about this....what gas did you pressurize the system with? This is exactly where I stand...it won't hold a vacuum, so I know I have a big leak in something I did, but I have no ability (at least yet) to pressurize with anything.

Ducman82

so when i did my system (just did), i had resigned my self to that if it would not hold vacuum, would be to re do all the connections. my main concern was the expansion valve o rings. so i made SUPER they had clean seats and the connections had good clean threads. my last "system" had a nice leak due to a chewed up o-ring on one of the compressor connections. it may be worth it to add dye and fill the system up, look for a leak, drain, fix and re charge.

bureau13

My system is still R12....Any harm in using R134a w/ dye, just to leak-check?

I was really thinking I could find someone to pressurize with nitrogen and find the leak, but haven't had a chance yet.

dr bob

So the deal with pressurizing with nitrogen is that it's DRY, so you aren't adding moisture to whatever is in there already. You can use almost any dry compressed gas, and nitrigen happens to be the cheapest. Next on the list is probably CO2.

Using the little Gast 'pump' to pressurize the system for leak-check isn't a great idea. Ditto using air from your home compressor, since both have compressed moisture in with the compressed air.

If you have a nearby tire store that offers dry nitrogen fills, you might try having them fill your portable tire-fill tank. But the tank already has moisture in it and no good way to get it out short of a good vacuum pump overnight with the tank warmed to coax the water out as vapor. Can you see how this all forms a big logistics circle?

jpitman2

Mate of mine used an old fridge pump to make a vacuum forming unit for moulding fibre glass. He left it running a bit too long and it crushed the article flat.
jp 83 Euro S AT 56k

harveyf

Easy for me cause I have a MIG welder and a TIG welder, both of which come with bottles of gas, but I used a couple of fittings to introduce the MIG welder gas into the system. Pressurized it to about 90 psi.

In answer to the question about using R134 in a R12 system for testing, I think it was AirTek who suggested this approach in another thread. That is what I did. Of course, if you are going the R12 route (which I did) you'll want to re-evacuate the system to get all of the R134 out. I also used a soap solution. The only significant leak I found was at one of the Schrader valves.

dr bob

Brings up a good point -- The o-rings at the Schraeder valves are old black crispy bits. When replacing o-rings in the rest of the system, the Schraeder valves need to be replaced too, with correct refrigerant-rated valves of course. With the green HNBR o-rings in them. For my S4 IIRC there are six total Schraeder valves to replace. The two obvious ones at the service ports on the car, one each under the pressure transducer and the low-pressure safety switch, and then the two on the compressor manifold.

When I swapped to R-134a fifteen years ago, I ended up removing the two from the service ports so the adapters would work correctly. The adapters had little depressor tabs on the female sides to open the Schraeder valves, but they ended up just bending the pins over. Since each adapter has its own Schraeder valve, it was an easy choice to just remove the one in the port underneath.

And for those playing along and perhaps not familiar, the charge hoses used between the manifold and the port on the car has a depressor in one end of each hose (red and blue). Make Sure that you have the depressor in the 'car' end so the valve is actually open, else the valve will stay closed until you put enough pressure on it from outside to push it open. You can preven the system from evacuating, and make charging a real chore if you forget this detail.

The depressors and seals on the hose ends are renewable parts. Seals particularly are an annual replace item if you use the gauges regularly. The depressors fall out when you aren't looking, or get mashed when overtightened on the dummy manifold ports. Hoses ALWAYS get stored with the ends closed.

Rob Edwards

I got an object lesson in this after volunteering to check the A/C in a neighbor's Acura TL. Only 25 psi residual pressure in the system- discovered a leaking low-side Schrader valve, with telltale oil and dirt around the connector. Bought a kit of valve cores and a core tool, replaced both valve cores WIWAIT, evacuated overnight. It held perfectly, so I recharged. Charge on an '04TL is ridiculously small- 540 grams (~$5 worth of r134a). Or maybe the 928 charge is just ridiculously large. Dunno.

harveyf

Oh crap Dr. Bob. I replaced mine with some I got from Ace Hardware I'll buy some of the correct ones now so I have them for next time. Any advice on where to get them?