Strange cooler operation (high superheat)

[PaulL]

Hi Everybody, hope you all are fine !

Please, I am posting here a case that is puzzling me

here is the case

I have an evaporator in a cold room with following set points

- air inlet temperature 0.32F
- evaporating temperature -27.4 F

Now starts the strange things.

I am measuring a superheating of 15K.
Yes, 15K !!

I made some verifications
- theoretical, with evaporator manufacturer, to see capacity in working conditions
- measuring air inlet/outlet temperatures. with manufacturer air flow I calculate a capacity similar to the one


all let convey that I can open the valve, so that I can get more refrigerant and therefore more capacity

But when I do this, I have fluid in compressor. All the compressor start to frost. Not only the beginning, the whole compressor.
The evaporator starts to frost in all rows

My interpretation is that there is a problem with the valve.

Please, could anybody give me an opinion about ?

as a general question.
What would happen if an expansion valve is not working properly ?


Many thanks !

[Brian_UK]

Is the room down to temperature? If not then wait until it is and then take another set of readings.

15K superheat, OK, has it changed from when you last checked the system?

[Rob White]

.

What is the refrigerant?

Where are you measuring the suction pipe temperature?

To get true evaporator superheat you need to measure both
the pressure and temperature as near to the outlet of the evap
as possible.

If you are measuring the pressure at the compressor there will always
be a slight difference. Also the refrigerant is important, is it a blend
or a single refrigerant? Is it a 400 series refrigerant or are you using R22?

Blended refrigerants (400 series) have a glide in the evaporating temperature,
it is very important that you know which side of the glide you are measuring.

If you are working with a blended refrigerant (400 series, zeotropic) you always
measure evaporator superheat from the Dew point temperature or sometimes it
is refereed to as the Vapour temperature.

Rob

.

[PaulL]

Hello, sorry for not being precise
- refrigerant is R507A, therefore no glide topics
- the most important element is that all the compressor starts to frozen when I open the valve, so that I get liquid going to the compressor, with the risk of damaging it.

[Brian_UK]

Then don't open the valve.

[Rob White]

Then don't open the valve.

:D

Rob

.

[hookster]

Hi Paul
Couple of checks to make:
Is the evaporator coil clear and air flow is correct?
Measure pressure and temp at evaporator as Rob says?
Check there is sufficient refrigerant in system.
Record suc & discharge pressures at compressor

[Sandro Baptista]

It's really strange the fact that with 15K superheat you get the vapour refrigerant temperature (evaporator outlet) at the same temperature the air inlet...meaning on theory you have a lot of lack of refrigerant flowing inside the evaporator. Where are you measuring the suction superheat? If you measure after a liquid subcooling heat exchanger with the vapour passing through it or if you measure the SH near the compressor of course an higher SH will happen.

[palmerm]

It's really strange the fact that with 15K superheat you get the vapour refrigerant temperature (evaporator outlet) at the same temperature the air inlet...meaning on theory you have a lot of lack of refrigerant flowing inside the evaporator. Where are you measuring the suction superheat? If you measure after a liquid subcooling heat exchanger with the vapour passing through it or if you measure the SH near the compressor of course an higher SH will happen.

If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.

[RANGER1]

If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.

Its always a possibility worth checking, but you would think it would flood all the time.
We are not hearing the basics of refrigerant charge, subcooling, piping detail, bulb position, way in which superheat is measured, air flow etc etc, so it's all guess work.

[Sandro Baptista]

If the liquid line passes through the suction line for subcooling sometimes this can crack putting liquid straight into suction line. This might be worth checking.

Palmerm, Ranger is right...it would flood all the time no matter what adjust you made to the expansion valve...