Checking composition of R407C

[nike123]

I have one of my blond moments.
If I want to check composition of R407 in refrigerant cylinder, what would be correct temperature to use for that check?
Is it dew point, bubble point, or middle point temperature?
I presume dew point, but I am not 100% sure.

[Quality]

I would of gone for bubble ponit

[binti]

I hate 407c.
If you think about it, if your checking the temp in the morning after a cool night the gas will be evaporating slightly, therefore i would go for bubble point.
If checking in the evening after a hot day then dew point.
I have found significant differences depending on the P/T chart used. So mid point may be the safest bet.
BUt like i said it's a turd of a gas. 7k glide???? suction super heat for dx system is 6k ish. work that out.

[nike123]

My plan is to keep suspected refrigerant in cylinder with new virgin refrigerant in same room at same temperature and compare pressures. If they are different, I will discard suspected one.

But I am curious to know what temperature I should compare with measured temperature by space thermometer.

When we speak about superheat and subcooling I know that we need to use bubble and dew point. When we calculating TD and approach, I know that we should use middle temperature. But I am not sure what to use when we are checking composition or non-condensables.

[doctor freon]

You should measure the cylinder pressure and compare to the dew point (saturated vapor) pressure on the R-407C PT chart at the ambient temperature. Comparison to a virgin cylinder will also be useful. Alas, the only way to know absolutely what is in the cylinder is a lab analysis using GC (gas chromatography).

[Tesla]

Hi niki123
You know what to check for but for accuracy I would be using a thermometer to check directly the refrigerant temp and press simultaneously with the refrigerant at a stable temp, and even then I would check it three times with a five minute interval. This would go for any refrigerant. Personally I use a yellow jacket ritchie. If it's a lot of gas I would do a quick check of calibration for the two sensors - my gauges are class one. As I understand with this zeotropic refrigerant the glide decreases with temp so the lower the better and there are two pt charts one for saturated vapor and one for saturated liquid. For logic I would be using the bubble point and measure the vapor temp of the refrigerant. It also depends on the application like flooded and capillary (differcult) and moisture is also an issue. I have only used this refrigerant a few times and going on by what suppliers and tech specs have taught me.

[Tayters]

An F-Gas trainer told me to measure the temp at the bottom of the cylinder (i.e. where there's liquid) and use the saturated liquid scale of the comparator.

In my mind I think of the refrigerant bottle and try and transpose it to a system then it's a reciever/condensor (ish!). That's how I look at it anyway. Therefore if there is only vapour left in the bottle you'd have to use the saturated vapour scale because transposing the bottle to a system it's an evaporator/suction line (yeah alright then, even compressor discharge).

I think the reason for measuring the bottle temperature near the bottom is for a more accurate reading as there would be more mass there.

Unfortunately that's the opposite of what Dr F reckons. QED: Dunno.

Andy.
<Scratches head>

[Tayters]

Gentlemen, may I present evidence in favour of my last post:

Bottle in the van about 3/4 full.
Standing pressure 76psig
Bottle temp top and bottom 4*C


On a comparator 76psig is 3*C on liquid scale and 9*C on vapour.

So I'm a degree out on liquid (bubble). Could be due to the thermometer as it doesn't read below a decimal point and I've not checked it against another one.

Case for bubble point m'lud.

Andy.

[nike123]

Good, now we know for sure that is bubble point temperature . I will check it tomorrow in a same way with borrowed Refco Digimon and surface thermometer on my virgin R407C bottle.

[nike123]

I checked this morning and it is saturated liquid temperature (bubble point) which was closest to my temperature measuring of cylinder temperature.
I measured 617kPa pressure and cylinder temperature of 6,5°C
If we consider measuring errors of both instruments (+-1°C of thermometer and 1% of pressure gauge range), than that is it.

Also I checked recovered R407C and its pressure was 525kPa at same temperature as original virgin R407C cylinder, and I decided to discard that recovered refrigerant.


Although I used Refco Digimon in this case successfully(only because resolution), but I don't recommend anyone to buy it, except as expensive toy for kids.
It is hilarious to use it as vacuum meter. You need to know your local barometric pressure to be able to compensate vacuum reading, which is, by the way, expressed as relative and it goes in negative value.
So I got -1006 mBar today as my vacuum level of my vacuum pump. So, I could tell that local barometric pressure is 1006 mBar.
More hilarious is micron value which is totally meaningless shown like this (and is actually shown in Torrs and on display it is written "microns". It is -754 "microns" on screen.

BTW temperature sensor which came with this model (model with Velcro) is useless, with bad contact (1/3 of its contact surface is covered with plastic from cable) which is actually on only one tiny point (because of circular shape of both pipe and sensor point and said plastic), slow response.

Pressure transducer of high side on this 15 day old meter is already faulty. I don't know is it from exposure to high pressure or some other cause, but guy which is borrowed it to me is swearing that it is newer been on pressure higher than 40 bar.

I took it apart and spressure transducers really looks like this is actually a toy:


Another perl:

Note: The DIGIMON must be powered ON before connecting the hoses and
switching on the vacuum pump. If this is not in the correct order the vacuum
display will not show the correct vacuum level.
Note: The DIGIMON must stay powered ON while pulling a vacuum. If the
DIGIMON is powered OFF while pulling a vacuum, the vacuum display will not
show the correct vacuum level.