Walk In freezer,r404

[johnanthonyhome]

Ok. Ill start with the box. Approx 8'x8'x8'. The system is a 5.5ton techumseh based. (aw series, rotolock 6500 btuh,low temp, high starting torque 3 phase) Overpowered to say the least. Anyway, the compressor failed after 15 yrs of service. I attribute the failure to repeat overheats due to faulty condenser fan connection, and clogged, undersised filter drier, coupled with outside temps in excess of 100 degrees. (south carolina) The box is located in a kitchen, with no walls exposed to outside. Said kitchen is at 88 degrees f. I replaced the compressor with the cross referenced 6100 btuh that techumseh recomends, which is still 5 tons-plenty.My current problem is that i cannot get the unit below 20 degrees, and i think I know why.I charged the empy unit to a head pressure of 275 psi. this put my suction at about 30, which corresponds to about 10 f. It instantly (20 min) pulled the box down to about 20 f. Came back next day. SAme. Put a thermometer on the suction line now, as i like to check superheat after unit has cooled awhile. Temp was 57 f. this line has no insulation on it, but also no ice. I think my solution is to insulate the pipe, and charge to a 20 degree super. That will probably put my coil temp up about 20 degrees, as well as my head pressure up 50+psi. So my hope is that with the correct superheat(20-40 for r404 at compressor) I will have a saturated evap coil which will pull down the air temp, and head pressure, respectively. Sound right to you guys? This is only my second low temp 404 application, and I'm hoping to call on your experience, as my background is in heat pumps, natural gas, and medium temp.

[nike123]

Is this system with TEV or with capilary tube?

[Peter_1]

Same thought Nike 123 but this is difficult to read.

Ohhh, welcome from Belgium.:o

If you post a question with the units you’re used to work with, place between brackets the other units. So if you normally work with SI units (bar, °C, m³/h..), place then between these units the proper IP units.

You can do the conversion with a free software program Uconeer
You can find it on http://www.katmarsoftware.com/uconeer.htm#download
Or you can use the spreadsheet of Dan posted on http://www.refrigeration-engineer.com/forums/showthread.php?p=50617#post50617 post 6.

Otherwise, your post will not be read by many members.

[johnanthonyhome]

txv....................

[johnanthonyhome]

txv? wait hmmmmm... that could be a problem hmmm

[johnanthonyhome]

Nope ,no balance tube, no bulb, its either piston or cap tube. I dont want to open evap case if i dont have to.

[Electrocoolman]

R404 wasn't widely in use 15 years ago?

What gas was system originally on?

Expansion device incorrect for gas?

[nike123]

Nope ,no balance tube, no bulb, its either piston or cap tube. I dont want to open evap case if i dont have to.

Do you have sight-glass? I think that you should open evaporator case and measure capillary length and diameter or find data about expansion device. What was full model name of old compressor?

[casstrig]

If I understood your last post you said the txv has no equaliser pipe or bulb making an automatic expantion valve completly unsuitable for low temperature work as there is no compensation for evap pressure drop and works much like a cappillary tube.Throw this away and replace it with an externally equalised txv.

[nike123]

If I understood your last post you said the txv has no equaliser pipe or bulb making an automatic expantion valve completly unsuitable for low temperature work as there is no compensation for evap pressure drop and works much like a cappillary tube.Throw this away and replace it with an externally equalised txv.

If you did not observed, this system has worked 15 years? And compressor has failed. Now we need to find reason why. I doubt that design problem will be hidden 15 years without damage.;)

[Andy]

Nope ,no balance tube, no bulb, its either piston or cap tube. I dont want to open evap case if i dont have to.

Hello Johnanthonyhome:)

are you getting subcooling on the liquid line?

What is your head pressure like?

Is the new compressor man enough?

Kind Regards Andy:)

[Peter_1]

Nope ,no balance tube, no bulb, its either piston or cap tube. I dont want to open evap case if i dont have to.

Piston or cap tube, learning every day.
What's a piston ?

[johnanthonyhome]

a piston is a drilled orifice, in a cylindrical piece of brass, hence the term piston. It fits into a cup which is soldered to coil feed tubes. The liquid line then couples to the cup, making for easier replacement. Using diferent pistons, one could use the same evap coil for diferent tonages. This is advantageous in hvac. Whereas the same air handler could be used for a 1,1.5,2,2.5 ton condensing unit.

[johnanthonyhome]

Is this system with TEV or with capilary tube?Thats it, Im opening the evaporator,cus if it is a txv-its either bad,or needs to be adjusted to new compressor. And your right, if its low temp-its almost certainly a txv. I will also measure superheat at the coil, as well as temps throughout the coil. Either way I'm thinking i have a starved coil-due to undercharge, or txv. I will be back with a solution, or more info. Thanks!~

[nike123]

Thats it, Im opening the evaporator,cus if it is a txv-its either bad,or needs to be adjusted to new compressor. And your right, if its low temp-its almost certainly a txv. I will also measure superheat at the coil, as well as temps throughout the coil. Either way I'm thinking i have a starved coil-due to undercharge, or txv. I will be back with a solution, or more info. Thanks!~


First check that, if it is TXV, that it is for R404A refrigerant!

[refmech]

:obuddy you need to check super heat at the valve. your going to get cold ,open up evap check tonnage [stamped on valve body],and charge of power head[note the colour of the tag]. get on the phone with a good supplyhouse rep. and get the right valve. check line connections[size/type]. install per instructions with valve, bulb placement is critical. clean pipe, insulate bulb. good luck.

[johnanthonyhome]

:cool: Problem resolved. Added refrigerant, brought superheat down to 30 faren. Head pressure high, opened txv 3/4 turn, corrected. Heres the kicker-opened thermostat to test-AND REALISED I HAD SET IT FOR -10 CELSIUS, WHICH IS +10 FARENHEEIGHT!!!!-CORRECTED. Runs like a swiss watch. Thanks

[icecube51]

good for you M8, so we all have learned a lesson here.

we Belgium's "the piston valve " :o
and the rest of you........, well i am sure you learned something.;)

thnx anyway,

Ice

[Peter_1]

Ice, lacht u bitje met je luuzn zeggen wij dan in de West Vloanders.:p
Wat vindt je trouwens van dit forum? Ik ben er wel fier op.

[jim thorpe]

Go to your local refrigeration house and give them the specifications of the box and they will give you the information on the proper mechanicals for both condensing unit, evaporator unit, txv, filter, and timer. Relace ALL OF THEM! Do not risk losing your customer by repairing a single component. The system is 15 years old. It did it's duty. it is time to be replaced. Sell this to you customer, or be married to a system that may fail down the road and even though it is not what you replaced, in the customers eyes you were "just out there and fixed it"

[icecube51]

sorry peter voor de late respons,maar ik denk dat ik al veel nieuwe aanwinsten voor het forum heb gedaan,ben er zeker trots op om mee te mogen doen.

Ice