Fieldpiece HG2 - HVAC Guide System Analyzer Manual do Utilizador descarregar pdf (Página 11)

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2.3 Superheat OUTPUT FORM

Figure 10. Superheat Test OUTPUT FORM.

Press OUTPUT for the Superheat OUTPUT FORM.

Target SH (Superheat): Indicates what the superheat

should be as calculated from outdoor dry bulb and

indoor wet bulb

Actual SH (Superheat): Shows the superheat calculated

from the measured suction line temperature and suc-

tion line pressure.

Boiling Point:  is is the saturation temperature of the

refrigerant in the evaporator coil. It is one of the tem-

peratures from which superheat is calculated.

 e

Actual SH (superheat) should be within ±5°F of

the Target SH to ensure optimum performance. If the

ac-

tual SH is outside this range, modi cations to the charge

or adjustments to the restrictor (TXV) are necessary.

Adding refrigerant lowers your Actual SH. Recover-

ing refrigerant increases your Actual SH.  e amount of

refrigerant necessary to add or recover will vary based on

the size of the system and the di erence between the Ac-

tual and Target SH.

Because everything within the system is inter-depen-

dent, one adjustment can a ect other parts of the system.

For example, increasing air ow increases the superheat,

which may require adding refrigerant. A er modi ca-

tions, allow 15 minutes to stabilize and then retest.

Superheat and Subcooling FAQ

Q: How do superheat/subcooling tools work?

A: Superheat tools measure suction line pressure and

suction line temperature, and calculate the actual su-

perheat. Subcooling tools measure the liquid line pres-

sure and liquid line temperature and calculate actual

subcooling.  e refrigerant charts for calculations are

incorporated into the so ware of the HVAC Guide

tester.

Q: When should I take my actual and target

superheat/subcooling?

A: Superheat and subcooling readings must be taken

when the system is in a steady state. Typically a resi-

dential system will be in a steady state a er 10-15 min-

utes. Turn the system on and set the thermostat low to

ensure that the system doesn’t turn o during your

testing. Once the system’s temperatures and pressures

are not  uctuating, the system is in a steady state.

Wet bulb temperature, outdoor dry bulb, suction line

pressure and suction line temperature must be taken

within a short time period to ensure valid results.

Conditions that a ect your target superheat and tar-

get subcooling can change by the minute.

Q: What do I do with my ACTUAL superheat

or ACTUAL subcooling measurements?

A: Compare actual readings against the target superheat/

subcooling. As a general rule, if superheat is too high,

add refrigerant. If too low, remove refrigerant. If sub-

cooling is too low, remove refrigerant. If subcooling is

too high, add refrigerant. Consult the manufacturer’s

speci cations before adding or recovering refrigerant

as further diagnostic tests may be needed

Continued on page 27

Sections of manual with more information

about this test.

If Target SH and Actual SH are more than

5°F apart, as in this example, you need to

make adjustments to the system.

Boiling point is used to calculate Superheat.

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 36 37

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