sight glasses

could some body clear up my confusion about charging to a full sight glass? Do some refrigerants need a full sight glass while others do not?

Hi Angry,
where is the sightglass fitted? Is one quetion springs to mind. If it is at the unit generaly charge to a full glass, but this is dependant on other things, head contol, prevailing ambient and system aplication. Realy you have to use your own experience, there is no good in chargeing a unit to a full glass on a freezer aplication and putting it out on head during pulldown, charge until the a point where the head is managable and wait for temperature pull-down.
Hope this helps.
Regards. Andy.

A full sight glass is your visual indication that you have subcooling. On any system employing a TEV, you should have at least a small amount of subcooling ahead of the TEV.

On systems employing a capillary tube or short tube restrictors, this is, of course, not the case. One should charge to a desired superheat with the systems, and not be too concerned with the quality of the refrigerant ahead of the expansion device.

As Andy points out, there are other issues to consider, particularly if you are replacing the refrigerant with one of the newer service replacement blends. For example, you may not have enough condenser to obtain the subcooling you want without running excessive head pressures. So you compromise. But having flash gas in the sight glass is not a "normal" condition, and the Prof has problems with blanket recommendations stating not to charge a system with a TEV to a full sight glass.

thanks for the information and fast responses guys. it is greatly appreciated!