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.
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.
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.
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.
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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.
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?
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
The cheap Delavel-type compressed air powered pumps easily pull 29". HF has one for $10 or so. JR Dweller in the cellar
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"Bill Noble" fired this volley in news:hsd7pl$8v6$ snipped-for-privacy@news.eternal-september.org:
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).
To the poster that mentioned the air compressor veturi type of vac gage - I used one of those a few years ago when I serviced the A/C on my wife's car. A poorly positioned clip chaffed thru a tube on the condensor. I found that the pump effectiveness was very dependant on ambient (or engine compartment temp). If I ran the engine to temp and then used the venturi vac pump, I could hear as moisture droplets were pulled out (I had replaced the filter along with the condensor). I never felt confident that I pulled adequate vacuum (never saw 29 in of Hg on the gage), but after 2 seasons, the A/C is still functioning well in her Saturn.
So what is considered an inexpensive micron / thermistor vacuum gage? After a quick search most of these gages run between $200 to $450. These would appear to be gages for daily professional use. I found one gage for $137
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expect to use this equipment once every 2 to 3 years.
Are there lower cost gages out there? I am a bit leary of a used gage
- concered about a used gage calibration / function. Would a dedicated vacuum gage such as this:
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better than relying on the manifold gage? If so, I would need to plumb it into the R134 manifold or connect it to my old R12/R22 manifold gage set and connect that to the other port on the A/C system during drawn down. With all the money that I will be spending on A/C parts, I do not have a lot of money left over for additional tools.
FWIW, my '91 F150 has suffered "black death". This Saturday I am going to play around with flushing the Condenser and Evap (presuming that I can get the broken off orifice tube out of the evaporator - was using an orifice removal tool and the end broke off anyway) but realistically I anticipate replacing condensor, evaporator and suction/ pressure hose (with integral muffler) along with the accumultor and compressor; so I would be pulling a vacuum on virtually a new A/C circuit.
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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.
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I got the Robinaire model you cited for $97 from Network Tool Warehouse
--
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. They frequently have really hot deals on refrigeration equipment. Apparently, they buy new stuff from factories, but also do large buys from distress sales, and offer the materials at pretty spectacular prices.
Don't overlook a U-Pullit joint as a source of used parts. I've gotten a lot of A/C related parts for cheap, whole compressors for $7 when all I needed was clutch parts, clips, clamps and other hardware. If you like living dangerously, you can salvage condensors and evaporators and flush those instead of your original contaminated parts. Very, very cheap compared with the cost of new. Also you can learn how-to on wrecks instead of messing up on your own stuff. I've rebuilt the compressors with new gaskets and seals and come out way ahead.
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