AC guys. Pulling a vac and knowing what’s happening.

Timco

What’s a good read to get more training on pulling a vac vs pump size vs bouncing numbers and such? I have a great leak free setup and do well (90 microns if I get distracted) but like to know it all.

Thanks.

ratio

I read a book called "A Review of Vacuum for the Service Engineer" some time ago. It's geared more towards industrial vacuum, they go over 12" vacuum lines, but a good read nonetheless.

Harvey Ramer

I think vacuum education is lacking by a great deal of HVAC techs. Kudos to you for seeking further education.

One thing to remember is, the size of your vacuum hoses has much more to do with the speed of vacuuming than the size of the vacuum pump. And just because you have a good vacuum at one end of the system doesn't mean the vacuum is good at the other end. Air movement is extremely sluggish and slow moving under deep vacuums.

Solid_Fuel_Man

Also the importance of cleaning your vacuum gauge as if there is any contamination (oil) your readings will be erroneous. Just Better has some really good videos and literature on the subject.

A micron gauge is a heater and a thermocouple, the rate of heat transfer is dependent on the vacuum in the system. You can see how that would be really skewed by oil contamination!

ChrisJ

Isolating the pump from the system with the micron gauge on the system side and shutting the pump down is important. This tells you how dry the system is and that you have no leaks. If it barely climbs after 15 - 20 minutes you can feel pretty confident the system is dry.

ChrisJ

Solid_Fuel_Man said:

Also the importance of cleaning your vacuum gauge as if there is any contamination (oil) your readings will be erroneous. Just Better has some really good videos and literature on the subject.



A micron gauge is a heater and a thermocouple, the rate of heat transfer is dependent on the vacuum in the system. You can see how that would be really skewed by oil contamination!

I see guys complaining about this constantly.
Not about "oil contamination" but about bad readings, and then claiming micron gauges are useless junk.

Keep the sensor pointed up to at least attempt to keep oil out of it, and then make sure it's kept clean.

GBart

here's a video on programming the sensor on yellow jacket micron gauges, I never knew this till recently

they also have a cleaning video if they become contaminated with oil, you have to clean them 6-12 times, another thing I didn't know

GBart

this is the one on cleaning, other brands are probably similar

Timco

Very good comments! I use a new JB DV-40S vac gauge that connects to my phone and a JB 7cfm that was just rebuilt. Under 200 it gives me the names of planets my vac has matched it pulls so low! It’s the ice, moisture, oil and other effects I’d like to master. I’ll get the above mentioned book coming soon.

EBEBRATT-Ed

Changing vac pump oil is important. Also temperature, look at the vacuum required to take moisture out as the temperature drops. If you have moisture and the temp is down in the 50s you will never get the moisture out

ratio

I just came across this on a different forum I visit. Again, not about refrigeration vacuum particularly, but an interesting read nonetheless. Talks about 0.000000001 micron vacuums... And I was proud of my sub-100 micron systems. <sigh>

JUGHNE

I had a 22 year old R-22 that appeared to have lost charge twice.
Over the long week end I tested the lineset and coil with 300PSI.
Held for about 72 hours.
The outside coil is pretty beat up from hail, checked it several times.
Was doing the vacuum pump on line set. I always do the triple.
First time was down to about 2000 microns. A little N2 flush and vac again. Wouldn't go below 3200. Turned the indoor blower on thinking warming the basement coil might help.
Still 3200, shut pump off and microns climbed to 4000..5000 and eventually atmospheric.
Added N2 up to 150 psi, you could hear the leak in the coil inside the case. One of the distributor tubes leaking as it went into the 3/8 tube of the coil.

I have never had this happen before. Hold 300 psi that long and then not hold vacuum. I believe when I turned the blower on the vibration loosened the joint. However the blower was on constantly during the 72 hour 300 psi test.
I guess this was a hit and miss leak situation.

O well, next week it gets a complete new system.