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  1. #1
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172

    Walk in cooler top of evap freezing up R409a

    I have a customer who owns a bar with a walk in cooler with R-409a, the evap was freezing up, I checked the system out, pressures and temps look fine, no defrost as its a cooler for beer and some food for the kitchen, medium temp 38-42. The first time there I saw a few bubbles in the sight glass on start up with a warm box customer shut it off earlier to thaw the coil for me. I blew out the condenser in the basement, checked the evap coil, checked the charge, all looked good the glass cleared shortly after start up, all looked fine with the charge, txv seems to be controlling superheat ok, has a danfoss txv. The top 1/4 of the coil froze up the next day and the box didnt come down to temp stopped at around 50. I ordered and replaced the txv adjusted the super heat, all looks ok except my high pressure is 180. The basement is HOT, 85-90 for sure and thats without the condenser running. So far as I know the coil has not froze up again, the customer said it would freeze up once in a while before but they would just shut it off thaw it out and it would be fine. My thinking is that with this condenser and the other two for the keg cooler and and the reach in cooler behind the bar all running down there that it is warm enough around the condenser to cause high enough discharge pressure so even though the txv is closed down as much as it can the higher head pressure is still forcing more refrigerant through the txv than needs be which explains why it sometimes freezes up and usually only during hot weather. Does this make any sense to anyone else, or am I way off? If I am correct would it be sensible to install a defrost heater and defrost stat? Or is there another solution?? A water cooled condenser in the basement would have made moere sense to me but I didnt install the system just responsible to keep the antique stuff running here! Always a challenge which I love.

  2. #2
    Join Date
    Jun 2012
    Posts
    37
    I would not be concerned with the head pressure. Even though your head pressure gets that high your expsansion valve should keep the pressure down in your evap. Condensing temps on units I work on with 409a in them this time of year hit 230psig or better. I would make sure the compressor pumps down (assuming this is a pump down system) when the pump down solenoid is de-energized. If its not a pump down system I would shut the high side down, probably with the king valve on the receiver, and see if the compressor will pump down. It sounds to me like the unit is never shutting off, never satisfying the t-stat, and freezing up because it has no off cycle to defrost. Get a superheat reading to find out what your evap is doing and an amp draw on your compressor.

  3. #3
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Yes it is a pump down system and it does pump down, I have pumped it down with both the electronic solenoid controlled by the stat, and by the king valve on the recveiever. My super heat was 8-10 at the txv bulb suction pressure about 42 box temp around 60. Maybe the old txv was just not closing down enough, like i said far as I know it has been fine since thursday night when I swapped out the txv. I guess my hi side isnt so bad at 180 if your running around 230! Thanks for the input I will check back in with the customer beginning of the week and see how it did for the weekend!

  4. #4
    Join Date
    Oct 2011
    Location
    Hull
    Posts
    53
    You need a timer and off time defrost.

  5. #5
    Join Date
    Jun 2012
    Location
    Wisconsin
    Posts
    118
    Does the walkin have ducts with fans running up with the beer lines? And how old is the walkin itself? I was working on a walk in with this situation with a cooler that was ancient and they couldnt figure out why the unit ran non stop. Also alota places like to leave the door open while they stock the coolers and shove alot of warm product. Maybe alot of extra moisture? I have seen coolers run without a defrost timer, but I think its just bet to have them installed.

  6. #6
    Join Date
    Jun 2012
    Location
    Wisconsin
    Posts
    118
    Also water cooled condensers i wouldnt think is a viable answer. Alot of places have water restrictions and just the shear water usage of the unit would be insane for a beer cooler

  7. #7
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    no duct for beer lines they just keep cases and kegs in the walk in. just has a standard evap coil in the cooler. The cooler is quite old and needs to have the seams sealed up which the owner wants to do, but the evap and compressor are fairly new, I believe they were new just before the place shut down the first time then when it re opened they didnt use the walk in for a few years. When I got involved in it the system had no pressure, replaced the dryer and sight glass pulled a good vacuum which held so I charged it up and have not had to add any refrigerant since and it has been running 2 years.

  8. #8
    Join Date
    Jun 2012
    Posts
    37
    With a box temp of 60 and suction pressure at 42 (about 48 degrees) I would say you might need to close off the expansion valve a little to get your temp down in the evap. I usually shoot for about a 20 degree colder evap than my box temp on a standard walkin cooler. With the box at 60 your superheat should be a little higher in my opinion because it's in a hot pull down. I wouldn't put a defrost timer on it because it has been running fine without one so there is no reason that a demand defrost should be needed all of a sudden. I have very few walkin coolers with defrost timers on them and the reason I have the few with timers is because they run a cold box (32-34 degrees) or because there is high humidity and lots of traffic in and out of the box.

  9. #9
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,150
    Quote Originally Posted by Jonnyb View Post
    You need a timer and off time defrost.
    Yep put a defrost clock in that thing.

  10. #10
    Join Date
    Jun 2012
    Location
    Wisconsin
    Posts
    118
    Quote Originally Posted by Flip14 View Post
    With a box temp of 60 and suction pressure at 42 (about 48 degrees) I would say you might need to close off the expansion valve a little to get your temp down in the evap. I usually shoot for about a 20 degree colder evap than my box temp on a standard walkin cooler. With the box at 60 your superheat should be a little higher in my opinion because it's in a hot pull down. I wouldn't put a defrost timer on it because it has been running fine without one so there is no reason that a demand defrost should be needed all of a sudden. I have very few walkin coolers with defrost timers on them and the reason I have the few with timers is because they run a cold box (32-34 degrees) or because there is high humidity and lots of traffic in and out of the box.
    I agree alota places dont have timers and probably dont need them... some places like there beer very cold, some dont care. Adding a Defrost timer does give the system flexability.

  11. #11
    Join Date
    Apr 2011
    Location
    michigan
    Posts
    172
    Thank you for the input I thought that my evap should have been cooler as well, but was trying to be careful being that the box was still hot and not make to many changes to fast. I was begining to second guess my call on the faulty txv. This walk in I think does get a lot of in/out traffic now as they have started serving food I think they started that around april not to mention the box is ancient and needs some air leaks sealed which the customer wants to do on their own to save on the cost. The other night when I was there it was so hot I was just ready to go home and cool off wasn't thinking as clear it was a long week with another long week ahead this week, but good thing is I am staying busy which I am thankful for. Thanks again for the input I will give it a check this week and see what the super heat is running now that the box should be at temp.

  12. #12
    Join Date
    Aug 2009
    Location
    Peoria IL
    Posts
    72
    I aways set up beer coolers and hi traffic walkins with heaters and time clocks just so i dont have so many calls for them leaving the door open or durning the high humidity in summer= frosted coils. sounds like your on track with the txv and hot box pull down 180 at 85 90 isnt bad did the txv hunt at all or no change. i would add a time clock for a off cycle and get some that heat out of the basement fresh air in hot air out good luck

  13. #13
    Join Date
    Sep 2008
    Location
    Cedar Rapids, IA
    Posts
    486
    Quote Originally Posted by Toddbrewster View Post
    Thank you for the input I thought that my evap should have been cooler as well, but was trying to be careful being that the box was still hot and not make to many changes to fast. I was begining to second guess my call on the faulty txv. This walk in I think does get a lot of in/out traffic now as they have started serving food I think they started that around april not to mention the box is ancient and needs some air leaks sealed which the customer wants to do on their own to save on the cost. The other night when I was there it was so hot I was just ready to go home and cool off wasn't thinking as clear it was a long week with another long week ahead this week, but good thing is I am staying busy which I am thankful for. Thanks again for the input I will give it a check this week and see what the super heat is running now that the box should be at temp.
    This time of year with high humidity and probably more beer moving in and out of the walk in. Your thermostat is probably not cycling very often. A box can defrost during the off cycle IF it gets a chance to shut off. You probably need a defrost clock (off cycle defrost) to assure the coil gets cleared in this weather/load conditions. Heaters shouldn't be necessary at a 38 degree box temp.

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