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  • Refrigerator freon charging

    OK, a couple years ago my Kenmore refrig was low on freon so the tech added a tap and put some freon in. Told me to add some more (R-134a) if the problem returned. No problem to add some in but do we have any techs here who know what pressure reading I should get when the correct amount of freon is added? Searching the internet gives a bunch of numbers around / under 10 PSI but obviously not from people who have any first hand knowledge or training. Anything bad happen when too much is added?

    Thanks.
    Steve

  • #2
    Yes, lots of bad things happen with a overcharge. R134A in a refrigerator should be below zero psi pressure, about zero to minus 4 would be about right. Technique is very important !!! If you let any air into the system bad things are going to happen. Because it runs below zero psi, you want to connect and disconnect your gauge lines with the unit off and after sitting a few minutes so that the pressure equalizes and comes above zero. The air has to be bled from the hoses also so that it does not enter the system. Also, I would expect the TOTAL charge to be in the area of 12oz or so of R134A, that is not very much! Small refrigeration units like this have what is known as a critical charge, standard practice is to weigh it in from empty but topping off is done by experienced techs at times.

    Small refrigeration units are the most difficult to work on.

    Comment


    • #3
      [QUOTE=Small refrigeration units are the most difficult to work on.[/QUOTE]

      That's an understatement to be sure. One of the key elements of small unit servicing is patience. You have to introduce an amount of charge, then wait for things to stabilize. They don't react quickly like auto A/C or home A/C units.
      Wayne

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      • #4
        Originally posted by Sparky_NY View Post
        Yes, lots of bad things happen with a overcharge. R134A in a refrigerator should be below zero psi pressure, about zero to minus 4 would be about right.
        OK, I'm confused. So, the blue gauge is measuring vacuum, not pressure? So why does the number go up when freon is added? If the line with the tap is running with a vacuum I'm guessing excess freon has to be vented with the refrigerator NOT running and after things stabilize. How long should that take? If it helps the data plate shows this refrig holds 9 oz.

        Steve

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        • #5
          Originally posted by SteveF View Post
          OK, I'm confused. So, the blue gauge is measuring vacuum, not pressure? So why does the number go up when freon is added? If the line with the tap is running with a vacuum I'm guessing excess freon has to be vented with the refrigerator NOT running and after things stabilize. How long should that take? If it helps the data plate shows this refrig holds 9 oz.

          Steve
          The blue gauge is for the "low side" or suction side of the compressor. Depending on the system, that suction line can run anywheres from a vacuum to over 100psi. The actual blue gauge reads both above zero (pressure) and less than zero (vacuum). Notice the numbers on the gauge less than zero? Most gauges are marked down to 30 inches of vacuum and up to 300psi pressure. The gauge can swing both ways of zero.

          As a example lets say a refrig is very low on freon and the gauge reads 20 inches of vacuum, as freon is added the pressure will increase, first to 10 inches of vacuum, then to zero psi then continuing to +5psi, then +10psi and so on. It will swing from vacuum, through zero and then to pressure.

          Final readings and adjustments MUST be taken after the system has cooled down close to its normal operating temperatures othewise you will not get proper readings.

          In the case of R134a in a low temp unit (refrigerator), yes it runs at less than zero pressure, just slightly less.

          Yes, excess freon would have to be vented with the system off, you only have to wait maybe 2 or 3 minutes after shutting it off and you will see pressure on the blue gauge. The 9oz nameplate charge is indeed a tiny one, its going to be very critical about the freon charge. This is the reason the charge is most commonly weighed into a empty system on tiny units like this.

          As a further note, its the freezer temp you want to monitor for performance, not the refrigerator side. Working properly it should be between zero and minus 15 degrees in the freezer.

          Small units like this can give even Pro's headaches in servicing them. The odds of you getting into trouble are quite high.
          Last edited by Sparky_NY; 09-27-2012, 09:32 AM.

          Comment


          • #6
            Originally posted by Sparky_NY View Post
            Small units like this can give even Pro's headaches in servicing them. The odds of you getting into trouble are quite high.
            LOL. And that is exactly why I'm asking for help from those who might know how these things work!!

            Your explanation is excellent. I'll go take some vacuum readings and see what I get.

            Thanks.
            Steve

            Comment


            • #7
              Sparky

              Update: Had a guy I know who does commercial and residential HVAC systems come over and he added some more freon and it was reading 12 PSI positive pressure. He said the extra pressure was no problem and it would just sit in the accumulator. Then I talked to a retired refrigerator tech and determined that knowledge of large HVAC systems does not necessarily apply to refrigerators since he also said overpressure is bad.

              Based on your info I decided to remove some of the freon and it now reads 3 PSI positive pressure while running. Didn't seem like I took out much to get it from 12 to 3 so I'm concerned about taking any more out since the retired guy also confirmed getting air into the system is bad. Right now the refrig is no longer making any gurgling sounds or other strange sounds it didn't used to make after shutdown and with the temp control in the middle position the freezer compartment is at 20 degrees F. My belief in not messing with things that are working is starting to kick in.

              Is this couple pounds of overpressure a problem and what parts might get damaged. Note that this whole drill is because the refrig is very slowly leaking freon (last top up was 3 years ago) and the problem will be going away over time.

              Thanks for the help.
              Steve
              Last edited by SteveF; 10-04-2012, 10:58 AM.

              Comment


              • #8
                Steve, You are getting close. In the old days we used to put in a bit to much freon, (R-12) back then, and then we would watch the frost line , when a unit is a little overcharged the suction line will frost up when the system is running. You don't want it frosting all the way back to the compressor. Sweating is ok but not frosting. Then we would let a bit of freon out and watch the frost line retreat back into the box. We kept this up a little at a time until the frost line just disappeared. Small friges don't usually have accumulators and are quite sensitive to the exact charge. Also when you are done the freezer temp will be lower. When it is back working and the compressor has cycled off for a while check your line tap with bubble soap for leaks. They often are a source of leaks.

                Comment


                • #9
                  I realize that I'm close, and the refrig is working acceptably well. Right now I know there is no air in the system and I'm concerned that I might accidently introduce some as I approach the vacuum state on that low pressure line. So, the question that I'd like to answer is, is there any chance of damaging something if I just let this overcharge problem resolve itself as it slowly leaks out or do I need to remove a little more freon?

                  Steve
                  Last edited by SteveF; 10-05-2012, 06:38 AM.

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                  • #10
                    I have heard of this method before.
                    It seems really good way to get the correct charge.
                    Too bad the hoses were not clear and you could see liquid or gas.

                    --Doozer
                    DZER

                    Comment


                    • #11
                      If your suction line is not frosting back to the compressor and is not sweating so much the side of the compresssor near the suction line is sweating you probably will not damage anything. It will probably will run a bit more and use a little more electricitry. The suction line accumulator your friend mentioned is used on larger systems to "boil away" any liquid freon before it gets back to the compressor. What will damage a compressor is trying to pump any liquid. This is why you always keep your freon can upright when you are charging. In my very early days I once toasted a car a/c compressor when I didn't notice the freon can had tipped over.

                      Is your fridge working well enough to be cycling on and off on its thermostat?

                      Comment


                      • #12
                        +1 on the frosting the compressor. The loside line should just sweat at the end of the comp. run cycle. It is my understanding that charging 134A MUST be done with liquid only. If the refrigerant fractionates the specifications are altered. R-12 etc. no problem with vapor charge.


                        Edit: atty is correct. I confused R134A with a different refrigerant. Vapor chg. is OK.
                        Last edited by Jim Hubbell; 10-06-2012, 06:01 PM.
                        Jim

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                        • #13
                          Actually 134a is pure compound, not a blend, so fractionating is not a problem.
                          Wayne

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                          • #14
                            Hi,
                            I realize that this thread is very old but I am curious as to the statement of keeping the can of 134A upright when, on the can it states to invert it.
                            Can someone shed light on this?
                            Thanks.

                            Comment


                            • #15
                              again A+ on the old school "watch the frost/cond line". Learned that 50 years ago and still useful. As far as can upright or upside, liquid charging is quicker but "could" result in the compressor intake of liquid and "slugging" .... plus when you disconnect the hose you might get an unpleasant surprise. ....wear safety glasses......I'm surprised at the casual sale and use of R134 particularly in auto a/c. Seems like they just throw more and more in there. It's a good thing the car computer keeps track of pressures and limits high side (disengages compressor clutch). There's no such safety on most domestic ref systems. :>))
                              Whenever I use a piercing tap to service a system, I use two. One low side and one high side. I like to KNOW what's going on in there...

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