Question regarding Torr gauges when pulling a VAC

[asmaircon]

Hi i would just like to know whether any of you guys out there have experienced the same thing as me, also if you have a cause for this problem and what it could be,

When using a torr gauge while vaccing out a a/c system usually splits, i have noticed once the vac has come down to about 0.80torr it sometimes seem to fluctuate going from 0.80 to 0.82 0.85 upto around 0.90 then back to 0.80 and going up and down in that region, this is after a 45bar pressure test for an hour or so with no drop in pressure.

Anybody know that can be the cause of this and is it a big problem?

Thanks

[james10]

If your getting that low don't worry about it

[Grizzly]

Probably moisture boiling off.
Have you ever given the vacuum long enough to stabilize.
Sometimes it can depend upon the refrigerant, meaning I have seen strange fluctuations in a system under vac.
When the refrigerant is a blend.
I am not a chemist or uber clever, but why if a blend can split at different positive pressures.
Could the refrigerant not do the same when under a deep Vac?
Just a thought!
Grizzly

[JoeAT50A]

Break with dry N2 and Vac again, 0.8 Torr is good enough I beleived (How is the climate in UK right now?).
Anyway 800 microns is pretty deep for split systems. Safe.. just forget about the rise. Your rise is nothing at all unless rising all the way around 1.5 or 2 Torr, then we could suspect on the moisture and leak.

[asmaircon]

Thanks for the repiles Joe the weather is quite mild for this time of year around 15 16 degrees normally its like 5-10 by now, the air conditioning is dying off now as its getting cooler also people dont want to fork out the bill for installations of air conditioning, so its quite tough over here in the uk and the economy doesnt help!!

[JoeAT50A]

Ambient 5 deg C and 800 micron is deep and you rise is just 0.1 torr. But just up and down in between and not rising anymore right, on top of that you have done 45 bar strength test as well. Don't worry so much on the rise, may be due to your Vac gauge.
We could able to say very safe and dry.
If you really want to make perfect deep evacuation, then break with dry N2 and vacuum again and hold.

[Boxer]

You need to triple vac the system to be sure,switch off the vac and see if the pressure rises in say half an hour. If it rises then you have a small leak or you have moisture in the system.Good luck !

[sweimaker]

guys 2 torrr is a sweet enough vacc.. 0.8 is some serious waiting time. do a standing vac test for 5 minutes (do u have a big kettle)

[asmaircon]

Hi i Have a Javac Vac pump and i seem to achieve 0.8 torr within about say 10 mins? on a 5metre pipe run, correct me if im wrong, these are pre charged brand new systems and the ports are closed ( wound in) with the pre charge in the reciever, this is still vaccing the pipe run and not the condensor? isnt it? also for the pressure test ports are closed until after vac then we release refrigerant

[Grizzly]

Hi asmaircon.
You are correct when vacing a new install, all that is vacuumed is the pipe runs.
Given that is you have used the plastic caps or taped open pipe ends, prior to their being made off.
All that your vacuuming is the small amount of moisture and air that may have accumulated within the pipework.
Which should be virtually none and any that had condensed out of this standing air within the pipework.
Should of been virtually eradicated by the nitrogen strength and pressurized leak test.
Not forgetting that if any fittings / joints have been used.
Then the purging with nitrogen whilst brazing will of reduced the contamination even further.

Therefore it is very easy to vacuum a new system.
The fun starts when the system is not new.

But that's another story.
Don't forget many of the vacuum levels quoted cannot apply when talking of large systems.

Grizzly

[croc1774]

Why pressure test to 45 bar ?

[asmaircon]

to make sure there is no leaks in the system, at a pressure of 45 bar running through the pipe work you will know whether there is a leak or not even just by hearing it as it is a very high pressure

[nike123]

What equipment you use to connect your vacuum gauge to system? What hoses, valves etc... and where are you connecting vacuum gauge in relation to system and vacuum pump.

With 45 bar for 1 hour you are not doing leak test. That is strength test, which is done after brazing of copper pipes to see if there is any weak point in installation (like at VRV/VRF commission).

After filing system with nitrogen, nitrogen is expanded when reaching lines from cylinder, and cooled by expansion. You need some time (usualy 1 hour) to nitrogen equalise its temperature with system, and than you could record your pressure and temperature, and be back after at least 12 hours (24 hours is preferable) and check for pressure and temperature change, and see for sure if you really have leak or not.

You can hear only large leaks and your vacuum gauge is probably correctly indicating some minor leak, probably at hoses or/and their connections or manifold valves stems.
Leak test by vacuum gauge should be looking like this:



So, you need some time to see leak.


What is important when vacuum drying system is not to use regular refrigerant hoses because they are permeable. You need specially made hoses for vacuum drying or flexible metal hoses and you should not use your regular manifold gauges. You need some special kit for vacuum drying like this one:
http://www.appioninc.com/products/cat-tools.html
which are designed to fast make and than hold good vacuum. They are rated to 20 microns (0,02 Torr).

http://www.youtube.com/user/HVACRat#p/u/11/_ISUGzoiui4
http://www.youtube.com/user/HVACRat#p/u/10/hCXNL0IWb1I
http://www.youtube.com/user/HVACRat#p/u/9/qdv77SyBgKE

http://www.mediafire.com/?zmyztx5gnzm