Subject : R 507


In , (johnny a. lopez) writes:

>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

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

From: (R80)

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.


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