OT Vacuum pump maintenance / repair

I purchased a used Robinair 15102-A vac pump last winter (much better price off season). Now I am ready to use it. I added oil (did not
replace the old oil since I was doing a test evacuation) and hooked the vac pump up to the vehicle's A/C system. I was able to pull 26 or 27 in of Hg of vacum. As I understand it I will need to pull 29 in of Hg to properly evacuate the A/C system (after repair).
Will changing the oil have an effect on the pump's performance (pull a stronger vacuum)? I searched for a manual or an exploded view of the pump with no success. What other sort of maintanence might I need to do to the pump? Other than hooking the pump up and letting it run, are there any other proceedures that I should / need to follow? Suggestions / links to info very much appreciated.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I do not know much about A/C systems or vacuum pump repair, but I do know that you can not pull more than the local atmospheric pressure which changes with altitutde and weather. For example, in Denver it averages 24.8 mm Hg.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
anorton wrote:

True. You'd almost want an absolute pressure meter (i.e. one that reads 24.8 mm Hg in Denver, and 0 in a perfect vacuum) rather than a relative one.
Or be ready to adjust for altitude...
--
Tim Wescott
Control system and signal processing consulting
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oops, my goof. That should be 24.8 in. Hg in Denver.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 11, 8:53 am, snipped-for-privacy@c3net.net wrote:

Oil will pick up all sorts of volatiles, I strongly recommend dumping the old stuff and putting in fresh. Keeping the intake and outlet sealed between sessions will help, too. You need vacuum pump oil, too, not just car oil. Just thought I'd mention that, you never know what some people will do...
Manufacturers sometimes will have rebuild kits, I know Welch pumps do. Used vac pumps can be a crap-shoot, you never know what kind of service the thing's been in, once a month, once a week, 24/7, you just never know. If it's been in the usual repair garage, nobody's changed the oil since it's been bought new.
Don't be too quick to blame the pump, a car A/C system has lots of leak potential, until you've replaced all the seals, you won't know what you've got. Attach the vac gauge directly to the pump and test it that way. Refrigerant sniffers have come waaay down, that would be my first choice for tracing leaks. Even HF has one, not that that's what I have.
Stan
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In order to be sure you've got all the moisture out of the system, you really need a micron gage. Your manifold gages aren't able to read the fine measurements you need.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Stormy, after the refrigeration sigs, I never thought I would see you mention HVAC again.
Yes... See my post (made after yours) about why/what/how.
LLoyd
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
What's a "refrigeration sig" and why would it have any effect on my posting?
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

SIG="special interest group". A newsgroup, in this case. The guys over there are pretty full of their own importance.
LLoyd
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I'd not heard that term used. Thanks for explaining.
There was a Dave From Illinois, who used to talk about the DG (discussion group). Fundy Dave used to post on alternating havoc usenet list, and rebuke us all as reprobates.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@c3net.net fired this volley in

You _cannot_ determine the degree of vacuum necessary to properly dry and fully evacuate a system with only mechanical gauges. You need a thermistor-style vacuum gauge. They aren't expensive.
I'll give you a scenario as to why. Yesterday (yes, actually) one of my employees asked if I could check out her Toyota's AC (which was blowing hot). yep. I grabbed the manifold gauges, the 134A adapter fittings, and the vacuum pump (Robinaire 6cfm). New oil, by the way. Always new oil -- AFTER every pull-down. Always. Never not. No excuses. ALWAYS... (did I say, "always, every time, no excuses, ALWAYS? If not -- ALWAYS, after EVERY pull-down on ANY system of ANY size. Oil is cheap, pumps aren't and inadequate pull-downs even less-so).
ANyway...
She complained that several people had "charged" her system using one- hose taps, and it was blowing hot. So I told her to go get two cans of 134A, and let me just pull it down. If it had a leak, we'd know. She could get the leak fixed professionally (I don't DO auto repairs except on my own vehicles).
I pumped the goop out of her system (full of leak-check and excess oil), then hooked up the pump and thermistor gauge, and let 'er run. I was hoping for 200 microns (mercury column) of vacuum. After three hours, it wouldn't drop below 400. That's sort-of a sign of a leak, but I had a clue that said, "no".
By the way, do you know what 400-micron vacuum looks like on a mechanical gauge? (clue -- about the same as 1000-micron vacuum)
ANyway... the average vacuum wouldn't drop below 400, but the thermistor gauge would occasionally dip to 275, then suddenly JUMP back to 400. That's not the way they normally work -- they move _gradually_ from point-to-point. They never jump -- unless. Unless there were droplets of water entrained in oil in the system, and they were progressively exploding into vapor, literally one-at-a-time.
Another clue was that the oil in the pump sight glass was growing cloudy. It never does that on a healthy system. Only on one with lots of water in it.
BTW... do you know what water looks like in a mechanical gauge? (clue -- about the same as no water, only there's an important distinction concerning how the system will work with or without it, and the gauges don't tell you that)
So... we let it run; All of 6 hours plus, actually. It pulled "droplets" for almost the whole time, gauge slowly moving down to 275, then jumping up to 400 again suddenly. Then, in the last 30 minutes, the thermistor gauge started indicating improvements. Eventually, it held 50 microns on pull, and rose to only 200 after being off the pump for 10 minutes. That's a good pull. No air, no water, nothing to interfere.
A quick re-charge was all that was left -- and you already know how to do that.
Quick answer -- no... you can't tell with mechanical gauges.
LLoyd
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message
interesting stuff snipped ----------

interesting post - I wonder if where you live matters
I have repaired a number of cars where the AC system is empty - mostly 944s in fact - swap the seal on the pump put in some of the new oil for R134, and fill - works fine. on one that exploded a hose in 130 deg weather, just replaced the hose (a few weeks later), and it worked fine. Never saw any moisture effects. So, why does your experience differ? could it be a drier climate, or could it be something else? Note, I am not questioning your advice/report, it makes perfect sense, I'm wondering why I can get away with not doing all that stuff?
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Possibly the systems you worked on were clear of moisture before you opened them, and you had them open for just a short time, so the amount of moisture in the system was minimal.
I do commercial HVAC service and all manufacturers recommend pulling a vacuum of 400 microns or lower to remove moisture from the system. If the system is new, and relatively clean you can reach 400 microns in minutes. On the other hand if the system has moisture in it it can take hours, or even days to pull a system down to 400 microns.
One time I vac'd a system for about 60 hours before it would hold less than 400 microns. The year before another service company replaced the compressor that failed. I replaced the compressor a second time, ran the vacuum pump for about 24 hours, changed the oil on my vacuum pump, purged the system with nitrogen and pumped it for about 24 more hours, changed oil on my vacuum pump again, purged the system with nitrogen again, them pumped for about 12 more hours. At this time the vacuum held at about 300 microns. That second compressor has been running for over 6 years. Greg
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

useful story snipped
In my particular case, at least one of these cars was open for several weeks while I sent the compressor out for repair, the one with the exploded hose was open for at least a week. I think the drier climate, and the fact that I wasn't operating the compressor with the system open might explain some of it - still, the very different results surprises me. I have pulled a vac (no, I don't have one of the "good" gauges) and just let the pump run overnight on one system - I didn't notice any improvement, but it wasn't worse either, compared to the ones that didn't get this treatment.
On my 59 cad, the car was empty of freeon for probably 30 years - I added freon and it worked (but leaked down after a year or so, I haven't recharged it in a long time) - but it was stored (in very poor shape) near Oildale - a very very dry area.
I wonder - maybe the careful treatment for moisture applies only when the humidity is above 5%? 10%?
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

This particular vehicle had - at one time - a leak on the low pressure side of the compressor. It had been run like that, recharged, run, recharged over and over without fixing the leak.
So it was sucking in non-condensables more or less continuously every time it ran out of refrigerant. In Florida, those consist of both air and prodigious quantities of humidity. The long pull-down was partly due to sucking the moisture out of the filter-drier (which can be re-dried with a long-enough pumpdown).
LLoyd
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I had thought filter driers were chemical system. And that you couldn't restore them. Maybe on cars, you can?
Yes, I easily imagine it drawing the system full of humidity. And of course, the compressor oil is hydoscopic.
--
Christopher A. Young
Learn more about Jesus
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
in

Some are calcium chloride-based, and only baking will dry them. Many contain "molecular seives". They're ceramic pellets about the size of #6 shot that have precisely-sized pores that will only admit and hold water molecules, while rejecting or releasing other substances. They can be "recharged" either by baking or by holding a hard vacuum on them for a time.
And yes, the oil is quite able to absorb a quantity of water -- in fact, that's part of its duty in a system. Water not in vapor form, and entrained like that isn't nearly as harmful to the system as hot vapor in contact with chloro/fluoro-carbons, or free liquid.
LLoyd
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 12, 7:19 am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

This must have been a cheaper vehicle. Most vehicles are built with a pressure switch in the low side which shuts the system down long before it pulls a vacuum on the low side.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

Florida - the place where you can walk into the ocean and not notice the change in humidity - that explains a lot
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Bill Noble wrote:

BS. There are no fish or sharks swimming in Florida's air. OTOH, ESD isn't a big problem here.
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
  Click to see the full signature.
Add pictures here
✖
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.