PDA

View Full Version : When is 407C not 407C, fractionation







robert.walters
24-09-2014, 12:10 AM
Hi All,

First post here.

When is 407C not 407C, fractionation.

We have just done a refrigerant analysis on a 407c system that had a leak in the aircooled condenser. We lost maybe 40% of the charge. Total charge 60lb.

407C make up is: HFC-32 (23%), HFC-125 (25%), HFC-134a (52%).
Test results today are:HFC-32 (27%), HFC-125 (28%), HFC-134a (45%).
This shows a 7% loss of 134a.

AHRAE states a tolerance of +-2%? I think.

Does this test conclusion constitute a full system re-charge?

Cheers, Rob W

PaulZ
24-09-2014, 12:07 PM
Hi Robert
The short answer is yes. Any of the new blends that have a high temp glide (more then 1 or 2) will fractionate and cause problems if the leak is on the gas side, this is the reason for liquid charging only.
One of the results of your above situation will probably be high discharge pressures.
Regards
Paul

joe-ice
24-09-2014, 03:30 PM
Thats very interesting seen as the other gases have gone up in percentage of the mix it appears mainly the 134a was lost. Im sure there is some type of equation can be done to show exactly what percentage of each gas was lost and what needs to go back in

hyperion
24-09-2014, 03:42 PM
Still the best and simplest answer is to find and repair the leak and then start again with new refrigerant charged in the liquid phase.

Rob White
24-09-2014, 04:16 PM
.

R134a tends to have the smallest atoms or molecules that make up the
whole refrigerant, that is why R134a mostly is lost first and that is
why you lose a higher % share of it in total.

The only people who can re-blend this is the refrigerant manufacturer,
the chance of you adding a bit of this and a bit of that to a fractured
blend and then getting it to the correct blend would be almost impossible.

You have a choice then! Do you remove it all and replace it with virgin
refrigerant or do you run the risk of adding refrigerant to the blend in the
hope it will be OK.

Chances are you might get away with it but if it is still blended wrong
afterwards then you will still have to remove it all and replace it.

I always tell anyone who asks to replace the whole lot if the total charge
is less than 10Kg. Below 10Kg it is not worth the hassle and the risk.

If the system is above 10Kg you, your company and the customer have
to make a commercial decision as to whether it is worth the risk of a
fractured refrigerant weighed against the cost of a complete regas.

Your decision and no easy answer because you just don't know what
state your refrigerant is before you start and what if the system had
leaked previously and already has had extra refrigerant added.

What on earth would be in the system is anyone's guess, unless you go
to the expense of having it analysed.

Regards

Rob

.

r.bartlett
25-09-2014, 11:01 PM
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1393&context=iracc

all you need to show the client is in here..

Rob White
26-09-2014, 02:25 PM
http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1393&context=iracc

all you need to show the client is in here..

Interesting document.

It shows what I thought would happen over successive leaks.
No system is perfect but some are more prone to leaks than others
and if you come to a fridge with 407 in it how many times before
has it been repaired?

If the paperwork and logs are all in place you could tell what had
happened over the last year or so but every time you add to 407
you dilute the mix to a point where it becomes useless to use.

Rob

.