R407c

[beebarron]

I have a mitz city multi system that was under performing. I decanted the gas (30kg) - and found that it was about 1kg short of the initial charge. I carried out a leak test and found a small leak on a flare nut.

I know that R407c is a composite of 3 gases and in theory you don't know what gases you have lost. But given that r407c is currently £36 kg - I'm temped to put the original charge + 1kg of new gas back in.

Would I just be wasting my time doing this - and should I opt for a new virgin charge or is it worth a try?

[Rob White]

.

I was always told if above 10Kg then advise customer and let
them decide, if below you would be better off replacing.
Just make sure the customer is aware of the situation.

The only trouble is, has it had other leaks before this one,
who knows what the blend is?

Some people work to a 5% - 10% rule, if the loss is less than
the percentage you use then add away if not replace with new.

Rob

.

[Tayters]

I'm no Mitsi guru but 1kg short out of a 30kg charge wouldn't have thought you'd have noticed the under performing.
If your leak was on a liquid line then you shouldn't have changed the composition. Back in my college days I remember the teacher saying the same also goes for a gas line too. The only place that will change the blend is a leak where the glide is. Needs someone brainer than me to confirm that but perhaps something to mull over.
Smaller glide I know but have seen plenty of Tesco packs topped up with 404 (back when it was cheaper!) and never had any grief.
Cheers,
Andy.

Another edit:
Came across this, see page 9.
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwjcybPm8KPZAhWLZlAKHTtYDjcQFggsMAA&url=https%3A%2F%2Fwww.honeywell-refrigerants.com%2Feurope%2F%3Fdocument%3Dr-404a-lgwp-replacements-in-commercial-refrigeration-oct-2014%26download%3D1&usg=AOvVaw08GURDIkfXVxlaxfrmhv0L

[beebarron]

Thanks. Decided I will drop in a KG and see what happens. That was interesting reading, re the effect of loss on composition. For years - id always been advised that any loss rendered the gas useless.But with gas prices spiraling out of control - it is useful to know, that there maybe some margin for loss without significant loss of performance of the gas.

[Rob White]

.

407C is a funny gas, they stopped using it in vrv's because of
the glide. 407C has about 7K glide and in some vrv's the
refrigerant fractures (fractionisation) and the refrigerant stops
working properly.

Another funny thing it does is it changes to 410A :)

R407C is made from R32, R125 & R134a and R410A is
made from R32 and R125 so because the 134a leaks
out first 407 turns into 410A.

:)

taz

.

[Grizzly]

.

407C is a funny gas, they stopped using it in vrv's because of
the glide. 407C has about 7K glide and in some vrv's the
refrigerant fractures (fractionisation) and the refrigerant stops
working properly.

Another funny thing it does is it changes to 410A :)

R407C is made from R32, R125 & R134a and R410A is
made from R32 and R125 so because the 134a leaks
out first 407 turns into 410A.

:)

taz

.

Hi taz,
Another interesting answer which confuses me somewhat!
So if a system leaks and the remaining charge becomes R410A.
What happens to the operating pressures?
Does not R410A work at much higher pressures
Grizzly

[Rob White]

.

Exactly, one of the side effects of 407 breaking down
is that the pressures go wappy.

Normally when refrigerant pressures change the high side
and low side change together, both up and down but when
407 breaks down the pressures go wappy. The discharge
goes very high but the suction goes quite low and it can
cause confusion if you have never seen it before. The trouble
is because leaks are different the pressures change differently
and not all faults show the same symptoms.

Rob

.

[RANGER1]

It would be interesting to hear how that happens theoretically.
From what I read here in link, pressure could go down, if anything, hopefully someone can explain to us.

https://www.wikihow.com/Calculate-Partial-Pressure

[Rob White]

.

As a blend if 407 was condensing at say 35degs c the pressure would be about 13 barg.
410 @ 35 degs c is about 20 barg

Glide has an effect with bubble and dew point differences but I have had so many conversations with engineers who have experienced high head pressure with 407 when it loses part of it's charge.

Rob

.

[Rob White]

It would be interesting to hear how that happens theoretically.
From what I read here in link, pressure could go down, if anything, hopefully someone can explain to us.

https://www.wikihow.com/Calculate-Partial-Pressure

Partial pressure of the gas when the gas is ideal but refrigerants are not ideal and I'm not too sure what happens when gasses condense into a liquid. Because the combined pressure of 407 is lower than 410 at any given temperature, the component that is different is the 134 and that makes a big difference.

R125 & R32 evaporate at similar temps at 0 barg (-50deg c) R134a is practically half that at about -26 Deg c so as the 134 leaves the system the 407 slowly turns to 410.

Rob

.

[Rob White]

.

Plus the molecular size of the 134 is smaller than that of other refrigerants.
134a leaks out of holes that don't exist so the 134a part of the refrigerant nearly always leaks out first when you have a weepy leak.
R134a will get where water won't :D

Rob

.

[cadwaladr]

Bring r22 back asap oh and r32 while we are at it,we now have more equipment that's got to be scrapped because new refrigerants are not compatible the world's gone barking mad

[cadwaladr]

Whoops spellchecker should have read r12! !

[nike123]

@Rob

What I concluded in my practice is that main problem of fractionation of R407C for use in VRV (and air-to water heat pumps with significant amount of refrigerant) is not in fractionation caused by leaks but with fractionation inside of refrigerant circuit. It tend to fractionate in suction accumulator if it is fitted. Small glide of R410a fixed that issue!

http://www.refrigeration-engineer.com/forums/showthread.php?12662-R407-and-suction-accumulator

[Glenn Moore]

I investigated many strange system problems with the 400 range of gases.
Several instances of fractionation happened on some supermarket systems which caused the systems to lock out on high pressure fault. The system charge was decanted to remove the over pressure and the systems re liquid charged. The cause of the problem was down to the condenser fans erratic control giving massive condenser pressure swings which caused the gas to fractionate and lock the system. Stabilising the condenser pressure solved the problem on these sites.
Poor condenser control set up can also cause poor system performance.
A number of system problems with poor performance I investigated were caused by excessive pressure drops in distributors .Several cold rooms could not reach there design temperature, and strange icing on the distributor leads and coil led to more investigations.
Pressure points were fitted after the expansion valve, on the distributor tube entering the coil block, and the evaporator outlet so that the pressure drops could be measured. Distributors and leads with pressure drops greater than 2 Bar seemed prone to poor efficiencies , and it seemed that the high pressure constituent of the gas had expanded during the expansion valve process ,and the high pressure drop through the distributor system caused a secondary expansion to take place which the cooling effect was done by the R134a constituent . By drilling out the distributor nozzle to reduce the pressure drop solved the problem. Having done this on a number of sites seems to prove that too high a pressure drop through the distributor system can cause the refrigerant to change its structure.
Most of these problems were on large coolers built to order i.e. the one offs but also on "off the shelf" coolers. These systems were on R407C ,R407A,R404A
Like most of you I'm not a chemist but with a little knowledge and trial and error solutions to these problems can be found