Service manual

18
Question: “What could cause the compressor to draw
overcurrent or to overheat?”
Answer:
1. “Dirty condenser coil.”
Check the appearance of the coil. If it is coated with
lint, cottonwood fuzz, leaves, etc., it is insulated and
it cannot give up its heat to the outside air. A dirty
condenser will cause high head pressure which will
in turn cause both high current draw and high
temperature at the compressor.
2. “Condenser fan does not come up to speed.”
Check fan blade, fan motor and capacitor.
3. “High or low voltage.”
High voltage can drive excessive current through the
motor windings. Low voltage can cause the
compressor to slow down, overload and draw
excessive current. Check the voltage between “C”
and “R” terminals on the compressor while it is
running. The volt meter must read between 103.5
volts and 126.5 volts (domestic USA models - plus
or minus 10%).
4. “Overcharge or non-condensables in the system.”
Either an overcharge of refrigerant or non-
condensables in the system will cause high head
pressure and consequently, excessive current. Be
especially suspicious if you discover evidence of the
system having been open (service valves in the
system, extra pinch off marks, etc.).
The indications of overcharge are:
a) Overcurrent which may be checked as
previously outlined.
b) Cooler than normal suction line. With an
overcharge, the suction line will usually
sweat all the way to the compressor.
c) Cooler than normal discharge line. The
discharge line should be highly superheated
and therefore, at high temperature.
Feeling lines with your fingers is a very inexact
method of gathering information and cannot be
considered accurate. So use this information only to
form preliminary judgements in your diagnosis of
trouble and consider as many indicators as possible
in coming to a conclusion.
The indications of non-condensables in the system
are:
a) Overcurrent
b) Higher than normal discharge line
temperature
c) Higher than normal liquid line temperature
d) Higher than normal compressor temperature
5. “Low Charge.”
This very rarely occurs and should be considered
only after all other possible causes have been
positively eliminated.
The compressor is dependent on a good supply of cool
suction gas for cooling. If the system charge is low;
there will be less than a normal amount of refrigerant
passing through the compressor, less compressor heat
will be carried away by the refrigerant, and therefore,
the compressor will overheat. NOTE – LOW
CHARGE WILL NOT CAUSE OVERCURRENT.
It will, in fact, cause the current to be low.
Indicators of low charge are:
a) The evaporator will be starved for liquid
refrigerant so the suction line and a portion
of the evaporator coil will be warmer than
normal. This is the condition we refer to as
too much superheat. How much of the
evaporator coil will be starved for liquid
refrigerant depends on the degree of
undercharge.
b) The active portion of the evaporator coil
which does have some liquid refrigerant will
be colder than normal and many times will
frost because the suction pressure will be
low. How much of the coil is active depends
on the degree of undercharge.
c) The compressor temperature will be
noticeably higher than normal.
Note: Low charge situations may be
mimicked by problems such as dirty filters,
dirty evaporator coils, air flow restrictions
and low load conditions. Do not attempt to
tap into the system unless you are
specifically trained in refrigeration system
repairs.