Superheat

[marc5180]

if you turn the screw on the expansion device half a turn how many degress would you expect it to rise or fall? Whats the general rule of thumb per turn?

[lana]

Hi there,

As far as I have read, there is no rule of thumb for this. Every manufacturer gives the info.
Also this changes with the model of TEV. For example for TE2 (Danfoss) half a turn gives some superheat change and for TE5, TE12.. (Danfoss), half a turn gives another change in superheat.

Cheers

[marc5180]

Ok cheers lana

[Gary]

if you turn the screw on the expansion device half a turn how many degress would you expect it to rise or fall? Whats the general rule of thumb per turn?

The general rule is: TXV's almost never go out of adjustment. Assuming it was adjusted properly to begin with:

If the superheat is high then:

a. The evap air in temp is high or...
b. The refrigerant charge is low or...
c. The inlet screen is plugged or...
d. The TXV is undersized or...
e. Somebody has been screwing around with the adjustment.

If the superheat is low then:

a. The airflow through the coil is insufficient or...
b. The system is grossly overcharged or...
c. The compressor is inefficient (broken valves) or...
d. The TXV is oversized or...
e. Somebody has been screwing around with the adjustment.

Sadly, the most common reason I have found for adjusting TXV's is "e".