Superheat

[SkyWalker]

hi guys i have learnt at collage how to messure superheat/sub cooling and i understand how its done. But on paper everything is "ideal".
I notice on alot of the kit i work on daikin/lg splits the restriction device is in the outdoor unit and is a cappillary so what "we" generally call the liquid line is actually the expansion line between device and evap, correct?

So anyway i want to measure the superheat of a toshiba unit which is on the site im working on. Would it be considerd correct to take the suction pressure at the service valve? and is it o.k to measure the temperature of the end of the coil just after the suction line flare nut at the indoor unit?

[Brian_UK]

I notice on alot of the kit i work on daikin/lg splits the restriction device is in the outdoor unit and is a cappilary so what "we" generally call the liquid line is actually the expansion line between device and evap, correct?

Yes.

Would it be considerd correct to take the suction pressure at the service valve?

It's about the only connection to the system that you will have on a 'split'.

and is it o.k to measure the temperature of the end of the coil just after the suction line flare nut at the indoor unit?

Yes, however....

It would be prudent to measure the suction gas temperature at the return to the condensing unit so that the overall superheat is being measured. Remember that you do not have a lot of control over the evaporator refrigerant feed on a split apart from confirming that the gas charge is correct.

The measurement of the superheat onto the compressor is important as that is the one piece of equipment that can really suffer if the superheat is too high or too low.

[LRAC]

Just thought i'd post this before people started asking about measuring superheat again.

To measure evaporator superheat:
1) Record the actual temperature at the TXV bulb.
2) Record the evaporating pressure at the TXV bulb.
3) Convert the evaporating pressure to temperature by using those handy
pocket pressure/temperature cards. These cards/charts show the saturation
pressure/temperature relationship for those refrigerants.
4) Subtract the temperature you converted on the pressure/temperature card
from the actual temperature you recorded at the TXV bulb.
5) The difference is the actual evaporator superheat.

To measure subcooling:
1) Record the compressor discharge pressure at the condenser or receiver.
2) Convert the discharge pressure to temperature by using the
pressure/temperature cards.
3) Record the actual temperature of the liquid leaving the condenser.
4) Subtract the liquid temperature (at the condenser) from the converted
temperature (from the discharge pressure using the pressure/temperature
card).
5) The difference is the amount of subcooling.

Kind regards
LRAC

[Brian_UK]

Good reminder LRAC, just wish they'd fit TXVs to splits sometimes