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  1. #1
    Join Date
    Aug 2008
    Posts
    107

    reach in R134a cooler

    A friend of mine has a reach in to keep flowers. The setpoint of the cooler is 47 degrees. It will maintain this temperature for a few days and then it will not drop below 70 degrees. It uses a cap tube system. It was originally R12 that was converted to R134a. The data plate does not have the weigh in charge and there is no high side port. I didn't have my tools on me when I looked at it a month ago. The condenser seemed to have a gradual decrease in temperature. There was little difference in temperature from the top of the condenser to the bottom. The temperature was higher than ambient temperature. I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up. With no weigh in charge data, I am going to have to charge the unit using a different method. I'm ruling out a restriction based on the fact that there doesn't appear to be refrigerant backing up and the lack of subcooling. I know POE systems with cap tubes have problems with restrictions.

    My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?

  2. #2
    Join Date
    Apr 2010
    Location
    West Virginia
    Posts
    636
    best this is call the manufacturer tech support they will tell you the orginial charge weight.

    If if works for a couple days then stops could be water in the system making its way around then freezing up and shutting the unit down.

    Jim

  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,485
    Quote Originally Posted by bluefitness View Post
    ...I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up...
    That sound of flashing is a good indicator that you don't have a solid column of liquid to the evaporator. The large amount of condensate water after shutdown would indicate an evaporator freezeup, as you suspected.

    Quote Originally Posted by bluefitness View Post
    My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?
    That rule-of-thumb may get you in the ball park but remember, it's just an approximation. As has been said, the best way is to get the proper charge weight for that box and charge accordingly. Short of that, use the superheat method.

    One old-timer's trick to get an initial charge approximation is to charge the system with the evaporator fan(s) off and charge until you get a frost line which just reaches the compressor. then restart the fans and complete the charge by superheat.

    Another one I use often, is to charge liquid to the high side (with the compressor off) until the flow stops. Then start the compressor and adjust the charge by superheat.

  4. #4
    Join Date
    Aug 2008
    Posts
    107
    Thanks for all the help. I called my friend to get the model number, but half of it is not legible. Since the design temp of this box is at a lower temperature 35 to 40, should I bring the box temperature down to this point before checking for a 20 to 30 degree superheat (I'm assuming I do). The box only needs to maintain 47 to 53 degrees; it is currently set to maintain 47 degrees. Another problem with this box is the ambient temperature can reach 95 plus degrees (located in unconditioned space). I doubt the cooler was designed for this temperature range. I will bring a saddle piercing valve (braze on type), since there isn't a high side port.

    I meant to write 22psig at 25sst in the original post.

  5. #5
    Join Date
    Aug 2008
    Posts
    107
    I looked at the unit yesterday:

    94 ambient
    33 psig suction (R134a)
    liquid line temp 114 to 122
    Temp difference through condenser 20 degrees
    Compressor running right at RLA

    The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).

  6. #6
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
    Posts
    487
    Quote Originally Posted by bluefitness View Post
    I looked at the unit yesterday:

    94 ambient
    33 psig suction (R134a)
    liquid line temp 114 to 122
    Temp difference through condenser 20 degrees
    Compressor running right at RLA

    The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).
    Get some more air on the condenser. Put a fan or an exhaust duct near it and make sure that none of the hot air is recirculting.

    You mentioned the unit was originally R-12 converted to R-134a. There is always capacity lost when this conversion is done and head pressures are usually higher. You could convert to R414b (hot shot) it has lower head pressures and less of a capacity loss. It will also work with either the POE or mineral oil.

  7. #7
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,431
    1st, check the door gaskets and make sure the door is closing properly. If that don't work....

    Has this thing ever worked since someone replaced the R12 with R134a? My bet is on the cap-tube being partially plugged up with burnt POE sludge. This would require a new cap tube, filter drier, and oil replacement and/or a new compressor. Like Bob says, R134a has less capacity than R12 did, and it runs at higher discharge pressures. R134a also is supposed to have POE oil which is much more prone to problems than other oils are, especially with the high ambients you are dealing with.

    If you are just messing around with this thing for the experience and challenge, and the customer is willing to pay for a bunch of parts with no guarantees, I say good luck! If you do try to fix it, try using Hot-Shot like Bob said, or R409a. Otherwise, it may be wise to try to get them to spring for a whole new flower cooler and send this one to the junk heap.
    Last edited by ammoniadog; 06-17-2010 at 10:37 PM. Reason: some questions I had were already answered in 1st post.

  8. #8
    Join Date
    Apr 2010
    Location
    West Virginia
    Posts
    636
    Quote Originally Posted by bluefitness View Post
    I looked at the unit yesterday:

    94 ambient
    33 psig suction (R134a)
    liquid line temp 114 to 122
    Temp difference through condenser 20 degrees
    Compressor running right at RLA

    The unit seemed to hover around 55 to 60 degrees. He said that it wouldn't go below 70 degrees after running for a couple of days, but he didn't remember the room temperature. I cleaned the condenser to no avail. I sprayed the condenser and the pressure dropped to 25psig and cycled off within a few minutes. The box temp is only set to 47 degrees. I pretty much told him that his problems were due to the high ambient conditions. Since I haven't done much commercial refrigeration work (mostly residential HVAC), I just wanted to make sure I'm not missing anything. I didn't add a high side fitting due to the liquid line temp. I guess I jumped to a quick diagnosis. I'm hoping someone can add some input, as the diagnosis leads to little to no solutions (other than moving the refrigerator).
    Your suction pressure is too high, 33psi 134a equals 38 degree coil = discharge air of 48 degrees.

    I will look back and see if you mention high side pressure, I suspect you are over charged by a good bit.

    Jim

  9. #9
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
    Posts
    1,431
    Something else that may be going on with this thing is since the temperature control is set so high, it may reach set-point and try to short cycle too quickly. If this happens, the little fractional horsepower compressor won't be able to start up and it will trip on its overload for a few times before it's able to get going again. If this is the case, you could wire in a delay-on-break timer or a different temperature control with a wider differential to try to help. This is probably in addition to the cap tube, filter drier, and oil replacement and/or new compressor. Have fun!

  10. #10
    Join Date
    Apr 2010
    Location
    West Virginia
    Posts
    636
    Quote Originally Posted by bluefitness View Post
    A friend of mine has a reach in to keep flowers. The setpoint of the cooler is 47 degrees. It will maintain this temperature for a few days and then it will not drop below 70 degrees. It uses a cap tube system. It was originally R12 that was converted to R134a. The data plate does not have the weigh in charge and there is no high side port. I didn't have my tools on me when I looked at it a month ago. The condenser seemed to have a gradual decrease in temperature. There was little difference in temperature from the top of the condenser to the bottom. The temperature was higher than ambient temperature. I also could hear flashing in the evap. I initially suspected it to be low on charge. My friend told me there is a large amount of condensate that came out of the unit after it was shut off for a while. I'm assuming the unit is icing up. With no weigh in charge data, I am going to have to charge the unit using a different method. I'm ruling out a restriction based on the fact that there doesn't appear to be refrigerant backing up and the lack of subcooling. I know POE systems with cap tubes have problems with restrictions.

    My problem has to do with charging a critically charged system accurately. I was taught to charge a system using a 15 degree SST below desired set point. For example, if you the box temperature was 40 degrees, the SST would be 15 degrees lower. Therefore, a 134a system would be have a low side reading of around 29 psig (25 degree saturated temp). Another way to charge it would be through superheat (20 to 30 degrees). Is this a proper way to check the charge of a unit or was I taught incorrectly?
    Now that I read again your original post, with the additional information you have provided I can tell you that the unit is why over charged.
    The original r12 had mineral oil which is not as problamatic as poe. I would remove the charge from the system. Start over, I can not tell you the exact amount of refrigerant but for the most part these have less than 12oz of refrigerant. I would go with 6oz to start, and make sure you have access to the high and low sides of the system and pump down, I would change the oil but that adds work. after adding the 6oz wait for at least 10 min then check super heat at the compressor suction line, then add 2 more oz, wait, and so on. You are looking for around 20 degrees superheat at the compressor.
    If you call around or post compressor model it will be easier to tell were you should end up.

    Or you could just remove gas, wait, remove wait and so on also. I personally would rather remove the gas and start all over.

    Jim

  11. #11
    Join Date
    Feb 2006
    Location
    Phoenix,AZ
    Posts
    2,895
    Put a high side access valve on it. And charge to 30 over ambient and then finish off with 20° SH at the compressor. Whats your high side pressure? 250?

  12. #12
    Join Date
    Jun 2001
    Location
    Michigan
    Posts
    12,077
    Quote Originally Posted by james122964 View Post
    Now that I read again your original post, with the additional information you have provided I can tell you that the unit is why over charged.
    The original r12 had mineral oil which is not as problamatic as poe. I would remove the charge from the system. Start over, I can not tell you the exact amount of refrigerant but for the most part these have less than 12oz of refrigerant. I would go with 6oz to start, and make sure you have access to the high and low sides of the system and pump down, I would change the oil but that adds work. after adding the 6oz wait for at least 10 min then check super heat at the compressor suction line, then add 2 more oz, wait, and so on. You are looking for around 20 degrees superheat at the compressor.
    If you call around or post compressor model it will be easier to tell were you should end up.

    Or you could just remove gas, wait, remove wait and so on also. I personally would rather remove the gas and start all over.

    Jim
    I have been not here much lately. seems you have come on the scene.

    Nice skills. welcome to the forum

  13. #13
    Join Date
    Aug 2008
    Posts
    107
    Thanks for the help guys.

    Here are the reasons I do not think it is a restriction:

    -Hot liquid line. 25 degrees over ambient
    -High suction pressure

    If it was a restriction, there should be high subcooling. Unfortunately, I did not take high side pressure readings, so I do not know the subcooling. With a restriction, the liquid should get backed up, and the liquid line temp should be closer to ambient. Also, with a restriction the suction pressure would be low. I have a SST of 38 degrees. I would think that the box could drop to maybe 53-55 degrees with that pressure. I was looking for a pressure around 22 to 25 psig. Also, when I spray water on the coil, my liquid line temp dropped and my suction dropped to 25 psig. The unit cycled off at 47 a few minutes later. I can not go by feel very well because I haven't worked on refrigeration enough. The temperature of the liquid line was so hot that I would know immediately that the condenser was dirty on an a/c unit. I know that high temp a/c diagnostics do not always carry over well to refrigeration, so I may wrong with some of my diagnosis procedures.

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