From: aschoen@mo.net
In
>To All: Tell me a little about 507, this is going to replace our med and low
temp R502 refrigerant in our rack system where I work. All I know is that it
runs a little high on head pressures. Allied chemical has convinced my
boss that this is the greatest since apple pie, friendly with the ozone.
We are located in the desert with designed temp 100f. Open for comments.
R-507 (aka AZ-50) is a 50-50 azeotropic blend of R-125 and R-143a. Its
thermodynamic properties are very similar to R-502 and, in general, R-502
system components need not be changed when converting to R-507.
Since R-507 is an HFC (hydrofluorocarbon), you normally need to use a
polyol ester refrigerant oil. Mineral and Alkyl benzene oils are not
miscible with HFC refrigerants. Usually the biggest headache converting
a system to an HFC refrigerant is getting enough of the existing
mineral or AB oil out of the system (>95 percent to be safe).
Your boss may want to consider one of the many R-502 service replacements,
e.g., R-402A, R-402B, R-407A, R-408A, if he doesn't want to bother
with clearing the system of its oil. These service replacements are HCFCs,
so they have a small ozone depletion potential. But they make converting
R-502 systems easier.
DuPont's R-502 HFC replacement is R-404A (aka HP62). It is a near
azeotropic blend of R-125/R-143a/R-134a (44/52/4). Its formulation
is close to R-507, and my above comments concerning R-507 also
apply to R-404A.
Andy Schoen
aschoen@mo.net
From: Peter Kesselman
R-507 (AZ-50) requires POE oil (95%). This makes for a more complicated
retrofit. That's why texts recommend AZ-50 (or HP62) for new systems.
An easier solution is to use HP80. This requires AB oil. However, you
can get away with as much as 50% mineral oil. We've used it in several
low-temp (-40) systems from 2 HP to 7.5 HP. Works great. Head pressure
is about 10% higher.
Peter Kesselman
http://www.smartlink.net/~pkay
Experiences with 507 (AZ-50)
I work for a major supermarket chain in the Chicago area and we have been
converting to 507 for about the last 8 months. We are using it to replace
low and med temp applications.
First, at least 3 oil flushes are recommended by Allied. 95% POE is
needed for 507. Have lots of filters handy I suggest the HH type.
With the combination of POE oil and 507 we have found that the mixture
moving thru your system will clean it very well. If there is a lot of
copper oxide scale inside your system from not using an inert gas while
soldering, you will have to clean txv screens several times. (Learned
from actual experience). Seeing that most of the contaminates will end up
the oil in the bottom of the compressor it is also advisable to have
filters in the oil feed line from the oil seperator to the oil reservoir.
It is amazing how fast the 507/oil combination will "clean" a system.
As far as high side pressures are concerned. The only big problem we have
had is when a whole rack was changed from 502 to 507. After recovery of
all the 502, a deep vacumn was pulled. Supposedly, the rack had been leak
checked before the vacumn was pulled. Several weeks after the new refrig
was installed the summer of '95 heat made its appearance, we starting
having hi press trips on the rack. The average running pressure was 280
to 310 #. This was on a low temp rack, ice cream and frozen foods. When
a system would come out of hot gas defrost the head pressure would creep
up to the hi press control setting and trip. (We use manual reset hi press
controls). Needless to say, after several frustrating service calls, it
was determined that somehow we had air in the system. We eventually got
rid of the air trapped in the condenser AND the reciever (thats where are
biggest air trap was). Now the head press runs about 240 on a 95 degree
day. So, on a retrofit, make sure there are no leaks before pulling a
vacumn on the system. It will drive you nuts trying to get rid of the
air(I should say non-condensables) in your system.
Another problem we have encountered is winter time operation with hot gas
defrost. Seems that 507 doesnt have as much "heat" during low head
operations. It has a tendency to make hot gas defrost take longer.
The above is just for information on a few problems that I have had.
Hopefully, a few more techs will share their experiences with this
alternate refrigerant.
Tech in the city by the lake.
R80@AOL.COM
From: r80@aol.com (R80)
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