On Apr 7, 11:40*pm, Toby wrote:
Tim+ wrote:
Toby wrote:
On 07/04/2013 20:52, Tim+ wrote:
Toby wrote:
Hello!

I have been given a freezer (Hotpoint FZ150) that wasn't working
properly, (after being turned on for a while, it would lock out and alarm
because it was not getting cold enough) - it had the signs of low
refrigerant, so I bought a set of gauges, and that confirmed it was
indeed extremely low, pulling down to about 18inHg on the suction side when running.

So, I bought some R600a refrigerant and then used an old freezer
compressor to vacuum the system out (after venting what little R600a
there was outside (As it is just butane, this is OK, apparently) The old
compressor got it down to just over 20inHg, which I was happy with for a DIY job :-)

My question is, how do I know if there is enough refrigerant in the
system if I check it at a later date without having to wait for it to be
so low it stops cooling and alarms? I weighed in the amount it stated I
needed on the data plate, but if it does need topping up at a later date
(which I assume is likely if there is a small leak somewhere (which I
will try to find)) then how do I tell how much is in there at any given time?

It's obvious, just weigh the whole freezer. ;-)

Seriously, with a refrigerant that's probably part liquid, part gas, a
pressure reading will be of no use to you. *That's why you put a weighed
quantity in rather than filling to a pressure.

Tim

I could weigh the whole freezer, but would then have to either track the
weight of the contents too, and also take into consideration the weight
of any frost build-up too :-)

Well, I did say "obvious", not "easy". ;-)

I can see the pressure readings while off will be of no use, as the
pressure will be the same no matter how much refrigerant is in there
(assuming there is some in liquid state), but when running, the high and
low sides should behave in a particular way depending on the type of
refrigerant and how much there is in there - I think it has something to
do with a pressure temperature chart like this
http://refspecs.co.nz/cms/uploads/fi...PT%20Chart.pdf

But I am not sure...

As the freezer appears to be working fine with the suction side at 0 when
running, maybe that is the answer...

Your seem to be well on your way to becoming a refrigeration expert anyway
so I suspect you know more about the subject than 99% of the folk here (me
included). ;-)

Tim

:-) been doing my homework! I was hoping there may be a proper
refrigeration expert lurking to fill in the gaps :-)

Also interested in a cheap leak detector for R600a and if it works on R410a
then that would be great too...

--
Toby... remove pants to reply

In days of yore when freon gas was used, there were special blowlamps
for detecting leaks that had a rubber pipe attached. The end of the
pipe was used to detect leaks, the flame changed to a green colour.
But that wouldn't work on butane.