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HVAC Discussions - Heating, ventilation and air conditioning.
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Posted by Lloyd E. Sponenburgh on April 17, 2007, 7:29 am
I'm learning the trade, and have installed four or five residential systems
under the eye of my instructor.
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.
LLoyd
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Posted by Bubba on April 17, 2007, 7:51 am
On Tue, 17 Apr 2007 07:29:22 -0400, "Lloyd E. Sponenburgh"
>I'm learning the trade, and have installed four or five residential systems
>under the eye of my instructor.
>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.
>LLoyd
Nice story, Mr Homeowner doing your own install. Id suggest you check
with your "instructor" and your "learning books" on the proper
procedures. Then, work with an actual tech as an apprentice for a year
or two and you should have all your questions answered.
Bubba
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Posted by Lloyd E. Sponenburgh on April 17, 2007, 8:43 am
> Nice story, Mr Homeowner doing your own install. Id suggest you check
> with your "instructor" and your "learning books" on the proper
> procedures. Then, work with an actual tech as an apprentice for a year
> or two and you should have all your questions answered.
My "actual tech" couldn't answer the question for the reason that he never
tried what I did. He doesn't spend 18 hours trying out an idea, because he
earns his living doing it. FWIW, not one of my textbooks lists anything
about passive pressure rise vs. time in an evacuated system.
And yes, DBCC actually offers the certification course, which is pretty
poorly attended. And yes, there is a severe shortage of _qualified_
technicians in this part of Florida. I'd like to become one who actually
understands my systems, instead of like the duct mechanic who answered
above. I wouldn't be studying my ass off every night for ONE system, or
shucking out what right now for me is big money on tools for ONE system; now
would I? And since I can't buy refrigerant yet, wouldn't it all be kind of
a waste?
Troll!
Does anybody besides this subhuman plenum crawler have a reasonable answer?
Obviously, Bubba can't figure it out.
LLoyd
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Posted by Noon-Air on April 17, 2007, 8:56 am
>> Nice story, Mr Homeowner doing your own install. Id suggest you check
>> with your "instructor" and your "learning books" on the proper
>> procedures. Then, work with an actual tech as an apprentice for a year
>> or two and you should have all your questions answered.
> My "actual tech" couldn't answer the question for the reason that he never
> tried what I did. He doesn't spend 18 hours trying out an idea, because
> he earns his living doing it. FWIW, not one of my textbooks lists
> anything about passive pressure rise vs. time in an evacuated system.
> And yes, DBCC actually offers the certification course, which is pretty
> poorly attended. And yes, there is a severe shortage of _qualified_
> technicians in this part of Florida. I'd like to become one who actually
> understands my systems, instead of like the duct mechanic who answered
> above. I wouldn't be studying my ass off every night for ONE system, or
> shucking out what right now for me is big money on tools for ONE system;
> now would I? And since I can't buy refrigerant yet, wouldn't it all be
> kind of a waste?
> Troll!
> Does anybody besides this subhuman plenum crawler have a reasonable
> answer? Obviously, Bubba can't figure it out.
> LLoyd
Maybe if your didn't start off with a bunch of bullshit lies, you might get
a more reasonable response.
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Posted by Lloyd E. Sponenburgh on April 17, 2007, 9:18 am
> Maybe if your didn't start off with a bunch of bullshit lies, you might
> get a more reasonable response.
Which lie? That I'm studying for my universal certificate? Or that I have
a local HVAC guy who's my friend AND my instructor? Or that I've installed
several systems with him guiding? Or that I've already started building up
my equipment list (including saving up for a recovery system)? Or that you
can't hire one in ten AC people in this area who actually know what they're
doing? Or that I'd like to be one that does know what I'm doing?
Which lie?
I guess this is like all newsgroups. You have to lurk for a while to know
who the assholes are, and who the real experts are. You can't all be like
these two.
LLoyd
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>under the eye of my instructor.
>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.
>LLoyd