I've started buying some tools: A Robinaire 6cfm vacuum pump, a Robinaire thermistor gauge, some decent manifold gauges, a leak detector, basic hand tools, etc.
My dad decided to "take the risk", and let me install his new upgrade system. I'm going to do all the rough work, then let my instructor check it out before he charges it. But since this is "my" system, and not just a "job", I decided to try an experiment, and it's got me a little confused.
My instructor tells me to evacuate the system by "pulling it down as far a the pump will take it" then letting it pump for a couple of hours more. My new pump with new oil has taken every system down below 50 microns.
But the Rheem manuals say you only need to go down to 500 microns.
Well, I hooked up dad's system, and pumped it down. Then I shut off the manifold port valves, shut down the pump, disconnected the center hose, and put the thing to bed overnight with the manifold gauge still connected.
I wanted to see how well it would hold up overnight.
18 hours later, I reconnected the center hose to the pump, and pumped down the hose until I was below 50 microns again. After letting that 'age' a few minutes with the pump running, I opened the manifold valves, and the pressure came back up to somewhere between 275 and 400 microns (finest steps on my thermistor gauge).
It only took about three minutes to drop that back down below 50 microns.
Sorry for the long narrative, but here are the actual questions:
1) isn't the Rheem 500 micron recommendation kind of HIGH? Especially considering that my pump will reliably go below 50? 2) Did the pressure rise overnight by what is really a small amount because of diffusion through the rubber hoses, or does that 300-or-so micron rise in 18 hours indicate a leak? I can't disconnect the manifold gauge with a vacuum in the system without leaking in even more air than that, so I don't have another type of test I can do for pressure rise.
Thanks... just learning. Hope to have my certificate in about another 8 months.