Freezer temp. control without thermostat.

[sukitlek]

This is my first question. I am new in HVAC and not good English. Sorry if using wrong English.

My old freezer (More than 10 yrs) have 2 tons compressor but TXV was only 1 ton (I don't know why) running without thermostat. The temperature was controled by dual pressure controller at condensing unit. Freezer room size is around 5' x 8' x 7'.

Now I need to change the TXV because the superheat is very high.(About 20 degree F) My question is "Can I change to 2 tons TXV?"

Thanks,
Sukitlek.

[Magoo]

More system information required, pressures and pipe run lengths. TEV are based on pressure drop across vav, for actual capacity performance, do not just read labels.
magoo

[sukitlek]

The condensing unit locate on the top of freezer then the pipe is not so long (less than 15'),
- The pressure between receiver tank and dryer is between 300-320 psig.
- suction of compressor is between 30-40 psig.
- suction line temp. more than 35

Last year the freezer worked OK about 20 F. But now temp. higher to 30 F., I cleaned TXV. (strainer and valve). During operating, Ice accumulate after TXV. at expand pipe from 1 tube to small many tube (about 3 inches after TXV.)

[nike123]

The condensing unit locate on the top of freezer then the pipe is not so long (less than 15'),
- The pressure between receiver tank and dryer is between 300-320 psig.
- suction of compressor is between 30-40 psig.
- suction line temp. more than 35

Last year the freezer worked OK about 20 F. But now temp. higher to 30 F., I cleaned TXV. (strainer and valve). During operating, Ice accumulate after TXV. at expand pipe from 1 tube to small many tube (about 3 inches after TXV.)

What refrigerant?

How much subcooling you have at receiver outlet? Any sight glass?

What is compressor model#?
What is TXV model#?
What is evaporator model#?
Pipes dimensions and equivalent lengths.
Height difference?

If your freezer worked OK and now it doesn't, than some problem is developed with its operation or you changed heat load.
MY first guess is: TXV bulb is lost its charge if subcooling is good.

[Shibhrac]

Dual pressure switch is usually the control method in walk_ins freezers. There is a thermostat which controls the solenoid valve.unless i know the refrigerant you are using it's very hard to guess correctly

[Shibhrac]

Dual pressure switch is usually the control method in walk_ins freezers. There is a thermostat which controls the solenoid valve.unless i know the refrigerant you are using it's very hard to make a correct guess.

[sukitlek]

Thank you and Sorry for less information.
- Compressor model is Copeland CRD1-0206-PFV-970 (Old model and equivalent to CR24KQ-PFV-980WB)
- TXV Sporlan QE-3/8x1/2x1/4 SAE-QC-2-KT-43-VZ
- The refrigerant is R22.
- Ambient Temp. 75-95 F for now

If the dual pressure switch is usually to cnotrol. I decide not change TXV to 2 tons and still change to 1 ton (The same old one). But after renew TXV. I would like to know, How much setting point the dual pressure controller, for High side, Low side and differrent setting.
I understand that low side use for temp. control in freezer room, High side to protect the compressor and diff. pressure for how long the commpressor restart, am I right?

[B G Scott]

This is like the old days and I mean 40 plus years ago, I was with Frigidaire and most systems had only control via LP switch, even in what were then considered to be super markets.
As an example we would set 38/42F applications to operate with a cut out pressure of 15psig and cut in at 33psig this gave off cycle defrost as well as temperature control.
I can't help feeling that progress does not always result in better or for that matter more economical products, some times just more complicated and more expensive. The KISS principle is still in my view the best route to reliability in most products

[nike123]

How much subcooling you have at receiver outlet? Any sight glass?



...................................

[nike123]

Thank you and Sorry for less information.
- Compressor model is Copeland CRD1-0206-PFV-970 (Old model and equivalent to CR24KQ-PFV-980WB)
- TXV Sporlan QE-3/8x1/2x1/4 SAE-QC-2-KT-43-VZ
- The refrigerant is R22.
- Ambient Temp. 75-95 F for now



I am not aware of any CRD1 compressor with 0206 designation. It should be CRD1-0200-PFV......

That compressor is designed for high temperature applications or air conditioning and freezer is not his intended use. He cannot go below 0°F evaporation temperature (around 20°F box temperature). His capacity is 12500 BTU/Hr at 20°F/120°F evaporation/condensing (7070 Btu/hr at 0°F/110°F evaporation/condensing).


3045

You should stick with that TXV since it is matched to your compressor capacity at freezer temperatures.
You could only change thermostatic element (after you prove that is faulty).

[nike123]

I would like to know, How much setting point the dual pressure controller, for High side, Low side and differrent setting.
I understand that low side use for temp. control in freezer room, High side to protect the compressor and diff. pressure for how long the commpressor restart, am I right?

Yes, you are right.

Settings:
http://sporlan.jandrewschoen.com/ColdWAR%20May%202009%20Pressure%20Control%20Setting%20Guide.pdf

[Shibhrac]

Wireless maintenance never give good results in your situation. It's better if you get the help of the one who made you learnt mechanical refrigeration

[nike123]

Last year the freezer worked OK about 20 F. But now temp. higher to 30 F.

20°F for freezer is not good temperature. What goods are inside?

[sukitlek]

Thank you very very... much Nike123.
The system have no sight glass. The subcool I did not check yet cause of no good temp. measuring device.(I just the one that interest in HVAC, Not a technician just DIY and just class I hvac certificate in FL. USA., But I will purchase the temp. measuring device tomorrow with new TXV).
- The freezer use for chicken breast and that temp.(20F) is good for slide the breast. If too cool it very hard to slide.

Thank you again. Nike123

[IMSTIEN]

Sir,
i would go back to 1 ton txv and recheck the settings on the low pressure control