Which vacuum gauge is right?

[cuervo]

A few days ago a co-worker and I got to do a evaporator coil and condenser coil changeout under warranty, due to the original coils leaking. Both of us are tool-aholics and we wanted to compare vacuum gauges.
Our vacuum setup included: fresh vacuum oil, Appion 3/8 x 1/4 hoses, Appion CRT's, standard 6 cfm vacuum pump, Yellowjacket vacuum tree at pump and all fittings with Nylog.
This is about 20 mins in.
My Bluvac never dropped below 1000 microns picture shows at 1037 microns. His JB held steady within the 270 range. Now being that the system was mainly new and only 2 places for oil and products of old refrigerant to stick around were compressor and lineset. Which gauge is right? We weren't expecting exact #'s but something within a ballpark.
We had a 3rd micron gauge a Fieldpiece and it was down in the 400 range.
What do you guys think?

[partime59]

how long did u let it sit to equalize,,, when pullin down the larger suc side line will take longer

[Tech Rob]

Where was the vacuum pump in relation to both gauges? Was it running at the time of the picture? I haven't found a digital gauge that I trust yet.

[itsiceman]

Was the JB on the liquid side or right on the vacuum tree near the vacuum pump? Thats far away from the spot where the BluVac was. I wouldn't expect the JB to show what the BluVac shows anyways since it is a ±5% of reading thru the entire operating range and the JB is probably more like ±20% in a small temp. range. They work best on a hot day. Use it on a cooler day and its worse IMO. The JB is so bad they dont even publish its accuracy. I love its giant display though.

[cuervo]

Parttime59..... the system is open for the pump in this picture. When we did allow to equalize Bluvac rose about 200 microns. JB held steady within a few microns.

TechRob...... We had to 2 Appion 3/8 x 1/4 hoses coming off the YJ tree that was on the pump. Hope that answers your question. Yes pump running and system open to pump.

itsiceman.... JB was on bull of Appion CRT on liquid line. Bluvac on bull of Appion CRT on suction line. Top of YJ tree was capped off.

[itsiceman]

I think if someone did a demonstration with some oil at various states in vacuum display like they have in science classes it would be easy to see why you did not go below 1000 microns on the BluVac in twenty minutes and show why you get the rise you see. It would also prove most the other gauges out there as not the same as a BluVac. IMO in twenty minutes your vacuum pump oil is just warming up on a cool day.

[Gunslinger]

You should have the micron guage pointing upward so it does not get oil logged. The Blue-vac appears to be pointing downward. I would clean it with alcohol.

[hvac wiz 79]

Id like to see another one in the equation. Like a yj

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[eddiegoodfellar]

I have used the Supco, the yellow jacket, inficon, cps, the Jb, and the UEI ( same as bluvac).

I trusted the JB the least and the UEI the most. Then JB would read 5000 microns when open to atmosphere.

[syndicated]

I have used the Supco, the yellow jacket, inficon, cps, the Jb, and the UEI ( same as bluvac).

I trusted the JB the least and the UEI the most. Then JB would read 5000 microns when open to atmosphere.

My supco does that sometimes. Don't know what's wrong, but everytime I use it beside the YJ it works correctly and reads the same, if only delayed a little.

[jim bergmann]

One thing to consider is if you were really leak tight. The Blu-vac will respond to any leaks much faster then most other vacuum gauges. If you had any leaks near the connections that gauges would read differently. About that only way to do what you are trying to do is to have everything hooked to the same connections and the same point on the system.

[stomper56]

It sounds like the system wasn't blanked off from the pump, so now your reading at two different points in the system.
When you blanked it off from the pump and let it stabilize what was your final readings? still above 1000 microns?

I would grab a empty recovery tank and put both gauges on there and see how long it takes to pull down, hold, and compare the two.

Getting use to the bluvac takes some patience, it wil make you question the vacuums you pulled in the past once you can read what its telling you.

Did you blow out the line set real well before you hooked up the new coils?
Typically on a new split system and line set it takes about 10-15 min to pull down below 500 and hold almost every time with a 50' line set.
However if i have to pull a coil for cleaning and replacement it takes at least 1-2 hours most times to get a good stable reading, usually go off to another call or grab something to eat when thats taking place.

Only difference in the between the two scenarios is the line set has been coated in oil, so longer vac times.

Whenever i have a system that stalls out on the micron gauge i break the vac with a low pressure nitro purge to get the molecules moving along through the system and out the pump.

Thats my experience anyway, hope it helps.

[Pascone10]

I had doubt in micron gauges as well so I did some non-scientific tests. My conclusion.. THey all like to read differently.. Some are way further off then others.. In my experience that Supernova gauge is JUNK..