cellor cooler

[mr saw]

nrs cellor cooler iced evap.defrosted connected gauges and switched on, pressures about 3bar -5 and 15bar +40 ambient +8oc. low side hunting on gauge checked tev found r22 tev and replaced with r4o7 tev orafice no 3. unit still hunting . any ideas......... details copeland scroll designed to run on only r407c. evap is an beermaster bme407-91 triple fan.
some of my ideas, mixed refrigerants..did not conduct press/temp test to verifie refrigerant

[aeb200]

The ambient temperature of +8oC -is that in the cellar or at outdoor unit?

If the 8oC is outside have you checked fan speed controller

If the 8oC is in the cellar then the superheat is too high -5oC to +8oC is 13oK superheat, evap is being starved (look at orifice size TEV adj.)

Is the piperun over a crazy distance or is there a large difference in height between indoor and outdoor units as
R407c can fractionate-
you may want to reclaim/evacuate and recharge with correct weight to eliminate mixed gas/contamiination)

[chillin out]

Short of gas?
Filter blocked?
Over-condensing?
Comp goosed?

Chillin:)

[iceman007]

Did you flush out after changing the expansion valve ? The different oils are not miscible, and I've had to clear up after other techs have changed the valve and refrigerant, but not bothered to flush out, very occassionally blockages can occur (quite rare though). Suction pressure sounds too low, assuming you adjusted the valve screw to correct superheat, then once you have done this you need to charge the system using the condensers subcooling as a reference because the superheat is held constant by the valve. Check that the coil (evaporator isn't fouled). The head pressure is too high for that sort of ambient outside temp- should be running at more like 12 bar or so- I reckon the TEV needs adjusting and the problems being caused by it shutting the refrigerant supply down and starving the evaporator (superheat needs to be about 5K, 8 at the most).

James

[frank]

then the superheat is too high -5oC to +8oC is 13oK superheat,
R407C vapour at 3 bar = -3C saturated.
Ambient temp of 8C does not eqaul a super heat of 13K :confused:

Ambient temperature has no bearing on superheat measurements unless the pipe is un-insulated and causes an increase in superheat

[iceman007]

Frank is quite right mr saw. Ambient temperature has nothing to do with superheat at all. I assume 8 degrees must be the outdoor ambient temperature, if so it's got colder I'm still freezing !!

Superheat is the difference between the saturation temperature of the refrigerant (i.e it's evaporating temperature at a given pressure, and the actual vapour temperature at the evaporator outlet-if that's where yu are measuring) R407c is zeotropic, so it has a temperature difference between it's bubble and dew point-in other words it's first constituent, in this case I believe R32, will evaporate at a slightly lower temperature than it's most stable constituent (the difference in temperature is the glide) You have to take measurements to get the superheat, but I would still guess that it's high, because I still think the TEV needs to be set to the right conditions.

At 8 degrees in the cellar-if it is that, then you would need to evaporate at about 1 degree or so-that's not superheat-you should usually evaporate about 7K lower than the air on temperature.

Enough said me thinks, I'm off to sit in front of the fire and have a cup of tea..

James

PS I shouldn't think the compressor is goosed it's running, and theres a good difference between suction and discharge sides.

[frank]

At 8 degrees in the cellar
Much too low for a cellar - should be 12/13C :) believe me - I know about beer :D

[iceman007]

Never thought about that !!! 10-14 degrees I think someone from the brewery once said, otherwise the beer goes cloudy and the pipe cleaning is a problem.
Cloudy bitter ??? Sounds like my local

[botrous]

If the 8oC is in the cellar then the superheat is too high -5oC to +8oC is 13oK superheat, evap is being starved (look at orifice size TEV adj.)

Superheat in an evaporator is defined as t1 - ps , where t1 is the tempreture mesured at the point on the evaporator where the expansion valve sensor is placed , and ps is the pressure measured at the same point . (the relevant pressure is converted to *C )

[botrous]

OOPS . . . I forgot the credits . . . the superheat definition i posted is took from this publication : Danfoss , Automation of Commercial Refrigeration Plant page 3.


Regards

[mr saw]

thanks for all responses, i need to clear up a few points. +8 deg is outside ambient. also how do you flush out a system with regards to oil change over. the new tev i placed in the system is straight out of the box and shouldnt need no adjustment.

[aeb200]

thanks for all responses, i need to clear up a few points. +8 deg is outside ambient. also how do you flush out a system with regards to oil change over. the new tev i placed in the system is straight out of the box and shouldnt need no adjustment.

Don't worry Mr Saw all the oil in the system will have come from the Compressor (precharged) If your system is designed for R407C then it will have a compressor installed with compatible oil- Replacement TEV's dont have any oil in them!!

Make sure that it wasn't the compressor that has been replaced!!!! If the R22 TEV is actually original and a R22 compressor that has been replaced with an R407C one - you've got problems!!

I still think that you may have an overcondensing problem caused by the recent low ambient - check fan speed controller. Also what made you decide to put orifice No.3 in the TEV? did you size it or did you phone manufacturers?

cheers aeb200
p.s. I didn't really think about my first reply - of course superheat isn't governed by off coil temperatures- you must all think Im a right dough-nut --- engage brain before typing!!! Lesson well learned

[botrous]

p.s. I didn't really think about my first reply - of course superheat isn't governed by off coil temperatures- you must all think Im a right dough-nut --- engage brain before typing!!! Lesson well learned

I appreciate your honesty :)

regards

[mr saw]

final update, solved problems. firstly fan speed controller electrically by passed because it dosnt work, hence always on and in this weather over condensing. filter before sv liquid line restricted and liquid line before tev twisted and bent hence causing restrictions. all these problems found on one job and am in process of repairs. thanks guys for all your help.

[Brian_UK]

Glad to here that the problem has been resolved, thanks for letting us know.

[sedgy]

hi bonita, all the above are from an old thread , 5 years old