While awaiting parts to arrive, I dug out my old Robinair 15400 pump and micron gauge. Both have been in a box for the last 18 years or so. Warmed-up pump and replaced the oil (with Robinair oil). Connected micron gauge and it pulled down to abt 180 microns within a couple of mins. This pump is rated at 15 microns. I think it will be good enough but wanted to see if there was a quick fix or if I need to install a seal kit. I suspect the shaft seal has hardened over the years.
Thoughts?
Improving vac pump perf
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JohnHere
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Re: Improving vac pump perf
If your vacuum pump will evacuate the system to about 500 microns, that's all you'll need. Ensure that the vacuum holds.
For an 18-year-old pump that evacuates to 180 microns with an oil change and a direct connection to the micron gauge, that performance is pretty good. Double-check your micron gauge that the sensor is clear of any debris and that it doesn't have any oil in it.
For an 18-year-old pump that evacuates to 180 microns with an oil change and a direct connection to the micron gauge, that performance is pretty good. Double-check your micron gauge that the sensor is clear of any debris and that it doesn't have any oil in it.
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Re: Improving vac pump perf
After messing with the hose connections, I'm now able to achieve 130 microns in 3 mins and down to 91 microns after abt 20 mins. Holding it is another matter. If I close pump isolation valve, vacuum goes over 500 microns in a few mins with just the micron gauge connected via 3 ft hose. Still not sure if it's moisture boiling off, hose outgassing or something leaking.
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JohnHere
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Re: Improving vac pump perf
A reading of ~500 microns, excellent for MVAC systems, is an extremely small, measured amount of vacuum that you can't even notice on a high-quality Manifold Gauge Set's low-side gauge in Inches of Mercury (InHg). That said, temperature, pressure, and material composition can also affect outgassing, and hence, rising micron rates.
When measuring vacuum with a micron gauge, outgassing of the material in an MVAC system—that is, the oil and desiccant (even if new), hoses, seals, and etcetera—plus air and moisture that might be trapped in the system, can affect the reading observed on a micron gauge.
The micron gauge should eventually "settle down" after evacuation to less than, say, 1,000 microns in an MVAC system, unless the system or equipment has a leak. Be aware that a micron-level leak probably can't be detected even by a sensitive electronic "sniffer" unless it's a substantial leak (non-micron-level).
The best you can do is to either change every o-ring, seal, and hose in your vacuum pump setup in an effort to prevent any equipment leakage, or (presuming your setup isn't leaking) continue evacuating until the micron gauge stabilizes to *some* arbitrary reading, unless the system itself is leaking.
When measuring vacuum with a micron gauge, outgassing of the material in an MVAC system—that is, the oil and desiccant (even if new), hoses, seals, and etcetera—plus air and moisture that might be trapped in the system, can affect the reading observed on a micron gauge.
The micron gauge should eventually "settle down" after evacuation to less than, say, 1,000 microns in an MVAC system, unless the system or equipment has a leak. Be aware that a micron-level leak probably can't be detected even by a sensitive electronic "sniffer" unless it's a substantial leak (non-micron-level).
The best you can do is to either change every o-ring, seal, and hose in your vacuum pump setup in an effort to prevent any equipment leakage, or (presuming your setup isn't leaking) continue evacuating until the micron gauge stabilizes to *some* arbitrary reading, unless the system itself is leaking.
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Re: Improving vac pump perf
Last night I played with it some more. Connected my brand new 3-port Fieldpiece manifold and all 3 brand new Yellow Jacket Plus II hoses to vacuum. Got down to 370 microns after a few mins. Shut-off pump isolation valve and shut-off pump. Today I'm at ~750 microns, so think I'm OK in regards to leaks with test equip.
Searching HVAC vacuum tests shows most recommend that sys should hold below 500 microns for 20-30 mins, and others say it should hold below 500 microns overnight. May be some are referring to HVAC systems other than automotive??
Don't think my system will hold below 500 microns for more than a few mins since the test equip by itself can't do that due to outgassing??
Anyway, I'm headed to the shop for what will certainly be a long crappy job. With a little luck, I'll have it evacuating this evening and see what's up.
Searching HVAC vacuum tests shows most recommend that sys should hold below 500 microns for 20-30 mins, and others say it should hold below 500 microns overnight. May be some are referring to HVAC systems other than automotive??
Don't think my system will hold below 500 microns for more than a few mins since the test equip by itself can't do that due to outgassing??
Anyway, I'm headed to the shop for what will certainly be a long crappy job. With a little luck, I'll have it evacuating this evening and see what's up.
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JohnHere
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Re: Improving vac pump perf
Calculate that 750 microns of mercury (µmHg) minus 370 µmHg equals 380 µmHg—or converting from microns, a mere 0.015 inches of mercury (InHg), you realize that it's not possible to even read such a very small amount of vacuum on the low-side gauge of your Manifold Gauge Set (MGS), which is most likely calibrated in *individual inches* of mercury. Since we're dealing with microns of mercury (µmHg) and not inches of mercury (InHg), I simply wouldn't worry about a minuscule difference on your micron gauge of 380 µmHg, and I'm guessing, neither would a pro shop.zz28zz wrote: Sat Oct 03, 2026 1:00 pm Last night I played with it some more. Connected my brand new 3-port Fieldpiece manifold and all 3 brand new Yellow Jacket Plus II hoses to vacuum. Got down to 370 microns after a few mins. Shut-off pump isolation valve and shut-off pump. Today I'm at ~750 microns, so think I'm OK in regards to leaks with test equip.
Professionals definitely wouldn't do this (time is money), but you could choose to continue to evacuate until you see the micron gauge stabilize at an arbitrary reading of, say, less than 1,000 µmHg, and call your evacuation procedure good.
HVAC (Heating Ventilating and Air Conditioning) refers to residential and business systems that are different from automotive systems, which are referred to as MVAC (Mobile Vehicle Air Conditioning) systems.zz28zz wrote: Sat Oct 03, 2026 1:00 pm Searching HVAC vacuum tests shows most recommend that sys should hold below 500 microns for 20-30 mins, and others say it should hold below 500 microns overnight. May be some are referring to HVAC systems other than automotive??
No need for evacuation to be a "crappy" job. I think you're getting too hung up now in the minutiae of the evacuation process. Just use your new MGS (forgetting about the micron gauge for the time being), evacuate down to ~29.9 InHg at sea level (higher elevations will yield a correspondingly higher vacuum reading), verify for 15 minutes whether the vacuum holds, and if it does, call it done.zz28zz wrote: Sat Oct 03, 2026 1:00 pm Don't think my system will hold below 500 microns for more than a few mins since the test equip by itself can't do that due to outgassing??
Anyway, I'm headed to the shop for what will certainly be a long crappy job. With a little luck, I'll have it evacuating this evening and see what's up.
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Re: Improving vac pump perf
Yes I'm aware you can't accurately read deep vacuum using a gauge set. That's why I have a micron gauge.
My understanding is that if you can pump down below 500 microns, isolate system and if it stabilizes and doesn't go above 1000 microns in a hour, there's no significant leaks. Just out gassing that stops at a certain vacuum level. Serious water vapor removal starts at 500 microns and below. New hoses are known to out gas due to solvent still in the rubber from the manuf process. In the past, I've included the gauge set in the evac process, but from what I've learned recently, it better to connect the pump directly to one side of the system and install the micron gauge on the other side.
Many years ago, I worked in a shop that did A/C work along with other automotive stuff. The "pros" are working against the clock and the system only has to last until the warranty expires. This, and the price of auto repair in general, is the reason I do my own work.
The crappy part is replacing everything and also doing some other "while I'm at it" items like new belts, idlers, and tensioners. Also pulled the radiator and gave it a good external cleaning. Had to flush evap and lines too.
C5 vette A/C systems are not designed to be worked on. Just to remove the compressor means pulling the right front wheel, drop the exhaust pipes, remove the batt and then remove the right side exhaust manifold.
The evacuation and charging is the fun part.
Got the A/C system closed up and purged with argon (don't have nitrogen currently available). Pressurized system to 125 psi and letting it sit for a few hours to see if I have any leaks. If that passes, will start the evacuation and finish putting humpty dumpty back together again.
My understanding is that if you can pump down below 500 microns, isolate system and if it stabilizes and doesn't go above 1000 microns in a hour, there's no significant leaks. Just out gassing that stops at a certain vacuum level. Serious water vapor removal starts at 500 microns and below. New hoses are known to out gas due to solvent still in the rubber from the manuf process. In the past, I've included the gauge set in the evac process, but from what I've learned recently, it better to connect the pump directly to one side of the system and install the micron gauge on the other side.
Many years ago, I worked in a shop that did A/C work along with other automotive stuff. The "pros" are working against the clock and the system only has to last until the warranty expires. This, and the price of auto repair in general, is the reason I do my own work.
The crappy part is replacing everything and also doing some other "while I'm at it" items like new belts, idlers, and tensioners. Also pulled the radiator and gave it a good external cleaning. Had to flush evap and lines too.
C5 vette A/C systems are not designed to be worked on. Just to remove the compressor means pulling the right front wheel, drop the exhaust pipes, remove the batt and then remove the right side exhaust manifold.
The evacuation and charging is the fun part.
Got the A/C system closed up and purged with argon (don't have nitrogen currently available). Pressurized system to 125 psi and letting it sit for a few hours to see if I have any leaks. If that passes, will start the evacuation and finish putting humpty dumpty back together again.