Undercharged Refrigerant Systems; Overcharged Refrigerant Systems - Friedrich PDE07K Service Manual

NOTE: In order to access the sealed system it will be necessary to install Schrader type fi ttings to the process tubes on
the discharge and suction of the compressor. Proper recovery refrigerant procedures need to be ad hered to as outlined in
EPA Regulations. THIS SHOULD ONLY BE AT TEMPT ED BY QUALIFIED SERVICE PER SON NEL.

Undercharged Refrigerant Systems

An undercharged system will re sult in poor per for mance (low
pressures, etc.) in both the heat ing and cooling cy cle.
Whenever you service a unit with an under charge of
re frig er ant, always sus pect a leak. The leak must be re paired
before charging the unit.
To check for an undercharged sys tem, turn the unit on, allow
the com pres sor to run long enough to es tab lish work ing
pres sures in the system (15 to 20 min utes).
During the cooling cycle you can lis ten care ful ly at the exit
of the me ter ing de vice into the evap o ra tor; an in ter mit tent
hiss ing and gurgling sound in di cates a low refrigerant charge.
In ter mit tent frost ing and thawing of the evap o ra tor is an oth er
in di ca tion of a low charge, how ev er, frost ing and thaw ing can
also be caused by in suf fi cient air over the evaporator.
Checks for an undercharged sys tem can be made at the
com pres sor . If the com pres sor seems quieter than nor mal,
it is an indication of a low re frig er ant charge. A check of the
amper age drawn by the com pres sor motor should show a

Overcharged Refrigerant Systems

Compressor amps will be near nor mal or high er. Noncondens-
ables can also cause these symp toms. To con fi rm, remove
some of the charge, if con di tions im prove, sys tem may be
over charged. If con di tions don't im prove, Noncondensables
are indicated.
Whenever an overcharged system is indi cated, al ways make
sure that the prob lem is not caused by air fl ow prob lems.
Im prop er air fl ow over the evap o ra tor coil may in di cate some
of the same symp toms as an over charged sys tem.
An over charge can cause the com pres sor to fail, since it
would be "slugged" with liquid refrigerant.
The charge for any sys tem is crit i cal. When the com pres sor
is noisy, sus pect an over charge, when you are sure that the
air quantity over the evap o ra tor coil is cor rect. Ic ing of the
evapora tor will not be en coun tered be cause the refriger ant
will boil lat er if at all. Gaug es con nect ed to system will usu-
al ly have higher head pres sure (de pend ing upon amount of
over charge). Suction pres sure should be slight ly higher.
lower reading. (Check the Unit Specifi cation.) After the unit
has run 10 to 15 minutes, check the gauge pressures.
Gauges connected to system with an under charge will
have low head pressures and sub stan tial ly low suction
pressures.
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