r12 walk in to 134a - Page 2
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  1. #14
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    Aug 2009
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    Maine
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    2,978
    If it isn't low on 409 can't you pump the system down using the receiver tank. At the same time you can check the compressor valves by keeping an eye on your gauges.

  2. #15
    Join Date
    Jul 2012
    Location
    Richland, WA
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    248
    Quote Originally Posted by lytning View Post
    If it isn't low on 409 can't you pump the system down using the receiver tank. At the same time you can check the compressor valves by keeping an eye on your gauges.
    Or you could recover, open system to do what you need, replace filter drier, vacuum and the return it to the system.


    Sent from my iPhone using Tapatalk

  3. #16
    Join Date
    Sep 2002
    Posts
    12,155
    Unless you have a very large evaporator coil, which isn't likely, even a generous 10º TD will have the coil running below freezing to achieve space temp. To avoid frosting would require less than an 8º TD. (40º minus 8ºTD = 32º coil temp)

    So; knowing that the coil is likely to frost - we have to refrigerate somewhat below the frost point so as to ensure that we can both maintain space temperature and allow the coil sufficient time to off-cycle-defrost. A cut-in above freezing will ensure a complete defrost cycle.

    I don't understand your concern about adding a LLSV - you are going to remove the 409 and convert to 134 anyway aren't you?

    What do you mean: you can't understand how it ran all these years? It can only be that the operating LP control was set properly, eh? <g>

    Do you know why Refrigeration Days have fewer hours in them than Human Days do?

    PHM
    ------





    Quote Originally Posted by kklobas View Post
    thanks everyone. PHM- why do you say 15lb cut out. thats only 12 degrees coil temp? it seems like it would freeze before then? i am concerned about the refer because to add solenoid i'll need to open system, and if i need any extra fefer after doing that, i dont have any.

    Can you elaberate on the time delay. specifficaly how it would wire in to the system?

    bunny- i'm with you that it wouldn't be abnormal to rise to 35 psi, just wandering how this thing could have ran for years with no t-stat or solenoid? original call i found coil froze solid,but pressure control was at 0psi cut out, 10 psi in, so that should explain the frozen evap.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  4. #17
    Join Date
    Mar 2013
    Location
    swan valley idaho
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    718
    my concern was only trying to do it as is without having to convert. If they decide to replace condenser it will definitely get changed over. I can not believe 0 psi was a correct setting for cut out on a beer cooler. i would have to think its froze over habitually with 0 and 10 settings.

    i do not know answer to your last question either..... lets hear it

  5. #18
    Join Date
    Sep 2002
    Posts
    12,155
    No matter what the application; all the heat has to be removed in a single Human Day. Each of which contain 24 hours. But for any coil which frosts, which is virtually all of them, some of the 24 hours we have to work within must be devoted to Defrost Time. Defrost Time must be subtracted from Refrigeration Time. This is why Refrigeration Days are shorter than 24 hours.

    Failure to understand this basic design concept is why quite a lot of refrigeration jobs are lean on capacity. Heat Gain never sleeps or even takes breaks so the total heat load has to be calculated on a 24 hour basis. But the removal of the total heat load must take place during a shorter time - so as to allow time for defrosting the evaporator. Whether it's off cycle air-defrost or a powered defrost cycle - it takes time.

    BTW: Hot gas, or especially reverse cycle defrost, is very fast - so the refrigeration equipment can be somewhat smaller. Electric defrost takes more time and so the refrigeration equipment has to be larger. To make sure that the total heat load is taken away in the shorter Refrigeration Day it has to work within.

    PHM
    ------




    Quote Originally Posted by kklobas View Post
    my concern was only trying to do it as is without having to convert. If they decide to replace condenser it will definitely get changed over. I can not believe 0 psi was a correct setting for cut out on a beer cooler. i would have to think its froze over habitually with 0 and 10 settings.

    i do not know answer to your last question either..... lets hear it
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #19
    Join Date
    Sep 2002
    Posts
    12,155

    So why do you want to do all these things?

    I'm sorry - I mis-read this before. I thought the goal was to convert to 134.

    Why would you entertain any of these 'fixes' you mention as opposed to simply setting the pressure control properly? Seems like it should have been a one hour service call. Maybe two if the LP is actually defective.

    Why do you want to do all these other things?

    Am I missing something here?

    PHM
    ------





    Quote Originally Posted by kklobas View Post
    so i looked at and old r12 walk in currently on 409. it has no t-stat or pump down solenoid just lp control. so i wanted to add t-stat and solenoid, but with 409 at 600 dollars a jug, cant justify buying it. may be a long long time until it all gets used. RSD suggested replacing condensing unit with a 134a unit, and then just use current txv and evap, add lls and stat. condensing unit and coil are both 10,000 btu, and looking at load calculations i should only need about 8,000 btu.

    so- with a good system flush, drier, and new condensing unit, does this sound like a decent plan? other thought was a 404a condensing unit, but unfortunately with the way the evap fits in this cooler i would have to take entire coil down just to replace txv because side access panels are blocked by cooler walls.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  7. #20
    Join Date
    Mar 2013
    Location
    swan valley idaho
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    718
    because i don't believe without a pump down and tsat it will work. when control shut it down it literally took about 7 seconds for pressure to rise back up to cut in. I thought a tstat and solenoid would be the correct thing to do. I will definitely try widening differential, but think pressure will rise to fast. its way old worn equipment i have to try and keep going a little longer you know?

  8. #21
    Join Date
    Sep 2002
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    12,155
    Does the suction pressure still rise if you stop the machine by closing the liquid line valve?

    PHM
    -------




    Quote Originally Posted by kklobas View Post
    because i don't believe without a pump down and tsat it will work. when control shut it down it literally took about 7 seconds for pressure to rise back up to cut in. I thought a tstat and solenoid would be the correct thing to do. I will definitely try widening differential, but think pressure will rise to fast. its way old worn equipment i have to try and keep going a little longer you know?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  9. #22
    Join Date
    Aug 2009
    Location
    Maine
    Posts
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    That will happen if the differential is set to close. Give it more of a spread. Could be crap in with refrigerant. Causes all sorts of weird stuff.

    Quote Originally Posted by kklobas View Post
    because i don't believe without a pump down and tsat it will work. when control shut it down it literally took about 7 seconds for pressure to rise back up to cut in. I thought a tstat and solenoid would be the correct thing to do. I will definitely try widening differential, but think pressure will rise to fast. its way old worn equipment i have to try and keep going a little longer you know?

  10. #23
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    Mar 2013
    Location
    swan valley idaho
    Posts
    718
    ok- set control at 19 cut out, 40 cut in. I'll give that a shot overnight and see if it's enough to keep this ol betsy running a few more months. thanks for all the input.

  11. #24
    Join Date
    Apr 2003
    Location
    Maple Grove, MN
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    1,235
    Does the compressor run off of a contactor? If so, a cheap and easy band-aid to accomplish what you want would be a "delay on break" time delay relay such as this one...
    http://www.grainger.com/Grainger/wwg...rue&sst=subset

    All you have to do is wire it in series with one of the wires going to the contactor coil and then set the dial close to the maximum setting.

    Using the pressure control instead of a thermostat IS a good way to control temperature, you just need some extra time and patience to get it set up correctly. As others have said, you get built in defrost control with this method, something you wont get with a normal thermostat.

    By the way, I like your description of the refrigeration day, PHM. That's good stuff!

  12. #25
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    Mar 2013
    Location
    swan valley idaho
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    unfortunately no contractor . could it wire in series with lp control

  13. #26
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    Aug 2009
    Location
    Maine
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    That time delay is good for less than 2 amps. You would burn it out in a second or 2. Very dangerous. You would need a low amps control circuit to do that.

    Quote Originally Posted by kklobas View Post
    unfortunately no contractor . could it wire in series with lp control

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