Refrigeration circuit pipes freezing

[necr]

Hi there,
My background is electrical. Out of curiousity, why do the refrigeration circuit pipes (outer circumference) freezes ( i.e pipe circumference covered with ice) now and then?

Thanks in advance

 

[quark]

Refrigerant appears in two states in any refrigerant circuit. The line from evaporator/chiller/indoor unit to compressor and from compressor to condenser/outdoor unit will be in gaseous state. The line from evaporator to compressor will be at lower temperature than atmosphere and moisture in the atmosphere forms dew(and subsequent icing) on the line. Refrigerant in condenser to evaporator will be in liquid state and any icing on the piping before thermostatic expansion valve indicates some obstruction to the flow and this is to be avoided in all cases.

There will be expansion of high pressure liquid refrigerant after TXV and partial flashing of the liquid into gas. So heat is again absorbed from the atmosphere and moisture forms dew on the pipeline.

PS: Provided, the lines are uninsulated.

Regards,

 

[chicopee]

what type of refrigeration system are you refering to?

 

[imok2]

The condition you describe can be caused by a slight shortage of refrigerant,a dirty evaporator, reduced air flow and anytime the evaporator coil sees a reduced heat load than that it is designed to see, a TXV can lose control and hunt. Hunting is nothing but the valve overfeeding and then underfeeding, trying to find itself.
Hunting occurs during periods of system unbalance (low loads), when temperatures and pressures become unstable.
The TXV tends to overfeed and underfeed in response to these rapidly changing values until the system conditions settle out, and the TXV can stabilize.
It is this overfeeding condition that hurts compressors. Too low evaporator superheat setting also causes the TXV to hunt.