Fieldpiece HG2 - HVAC Guide System Analyzer - Manual (Page 22)

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5.407 High airfl ow, possibly reduce airfl ow: Th e
indoor coil airfl ow was directly measured using the
TrueFlow grid and is higher than expected. Consider
reducing the airfl ow particularly if the unit is in a
damp climate. In heat pumps high airfl ow causes un-
comfortably low delivery temperatures.
5.408 Possible plenum temperature measure-
ment error, retake plenum temperatures:
Th e reported wet and dry bulb temperature readings
from the return and supply plenums are unlikely. Re-
take the measurements in the INPUT FORM. See Re-
turn DB and Return WB sections for detailed instruc-
tions on how to take these measurements properly.
5.5 Refrigerant Charge
Incorrect refrigerant charge is the most common
problem with air conditioners and heat pumps. Th ere are
widespread poor practices and misinformation regarding
refrigerant levels.
Th e primary method specifi ed by major manufactur-
ers for non-TXV (fi xed metering device) systems is su-
perheat. Th
e superheat needs to be matched to the target
superheat, which changes with indoor and outdoor condi-
tions. Th
e optimum refrigerant charge as indicated by su-
perheat is aff ected by the airfl ow across both coils. Repair
any airfl ow problems before setting the fi nal refrigerant
charge.
Th e primary method for TXV or EXV systems is
subcooling. Th e subcooling needs to be matched to the
target subcooling. Th e target subcooling is usually on the
manufacturer's ID plate along with the model and serial
numbers.
For heat pumps, it is best to set the refrigerant levels
in the summer in the cooling mode. Th e HG2 can also
check the capacity of heat pumps in the winter as an indi-
cator of correct refrigerant charge.
5.501 Charge OK: Refrigerant charge was tested us-
ing the appropriate method and it is OK.
5.502 Possible OK charge: Th e primary indicator of
refrigerant charge (subcooling for TXV/EXV or su-
perheat for non-TXV) indicates the refrigerant level
was OK. However, a secondary indicator reduces the
confi dence in that diagnosis. Check out any other po-
tential problems indicated.
5.503 Charge unknown, check charge: Th e mea-
surements are insuffi cient to diagnose the refrigerant
charge. For best results, measure both the suction line
temperature and pressure as well as the liquid line
temperature and pressure and press the OUTPUT
button again.
5.504 Possible undercharge, possibly add re-
frigerant: If no other conditions are triggered, con-
sider adding refrigerant to correct. Th ere is possibly
insuffi cient refrigerant in the system. Th e amount of
refrigerant necessary to add will vary based on the
size of the system and the diff erence between Target
and Actual superheat/subcooling.
5.505 Probable undercharge, add refrigerant:
It is very likely that there is insuffi cient refrigerant in
the system. Add refrigerant to bring the superheat or
subcooling to within the target.
5.506 Undercharged, add refrigerant until ac-
tual superheat reaches target superheat: Th is
non-TXV system is low on refrigerant. Add refriger-
ant until the superheat is within the proper range
(usually ±5°F) of the target superheat. Th
e closer the
superheat is to the target, the better.
5.507 Undercharged, add refrigerant to obtain
6°F of superheat: Th is non-TXV system is low on
refrigerant. Since the test conditions are hot outside,
dry inside, or both, the exact target superheat cannot
be determined. Because the superheat is greater than
6°F the unit is undercharged. Add refrigerant until the
superheat is 6°F.