Friedrich 2007 - Manual (Page 11)

11
IMPORTANT
ANY SEALED SYSTEM REPAIRS TO COOL-ONLY
MODELS REQUIRE THE INSTALLATION OF A
LIQUID LINE DRIER. ALSO, ANY SEALED SYSTEM
REPAIRS TO HEAT PUMP MODELS REQUIRE THE
INSTALLATION OF A SUCTION LINE DRIER.
the liquid refrigerant leaves the metering device entering
the evaporator coil. As it enters the evaporator coil, the
larger area and lower pressure allows the refrigerant to
expand and lower its temperature (heat intensity). This
expansion is often referred to as “boiling”. Since the unit’s
blower is moving Indoor air across the fi nned surface of
the evaporator coil, the expanding refrigerant absorbs
some of that heat. This results in a lowering of the indoor
air temperature, hence the “cooling” effect.
The expansion and absorbing of heat cause the liquid
refrigerant to evaporate (i.e. change to a gas). Once the
refrigerant has been evaporated (changed to a gas), it is
heated even further by the air that continues to fl ow across
the evaporator coil.
The particular system design determines at exactly what
point (in the evaporator) the change of state (i.e. liquid to a
gas) takes place. In all cases, however, the refrigerant must
be totally evaporated (changed) to a gas before leaving the
evaporator coil.
The low pressure (suction) created by the compressor
causes the refrigerant to leave the evaporator through the
suction line as a cool low pressure vapor. The refrigerant
then returns to the compressor, where the cycle is
repeated.
Liquid
Line
Suction
Line
Evaporator
Coil
Metering
Device
Refrigerant
Dryer
Discharge
Line
Refrigerant Drier
Condenser
Coil
Compressor
Refrigerant System Components
A good understanding of the basic operation of the refrigera-
tion system is essential for the service technician. Without
this understanding, accurate troubleshooting of refrigeration
system problems will be more diffi cult and time consuming,
if not (in some cases) entirely impossible. The refrigeration
system uses four basic principles (laws) in its operation they
are as follows:
1. “Heat always fl ows from a warmer body to a cooler body.”
2. “Heat must be added to or removed from a substance
before a change in state can occur”
3. “Flow is always from a higher pressure area to a lower
pressure area.”
4. “The temperature at which a liquid or gas changes state
is dependent upon the pressure.”
The refrigeration cycle begins at the compressor. Starting
the compressor creates a low pressure in the suction line
which draws refrigerant gas (vapor) into the compressor.
The compressor then “compresses” this refrigerant, raising
its pressure and its (heat intensity) Temperature.
The refrigerant leaves the compressor through the discharge
line as a hot high pressure gas (vapor). The refrigerant enters
the condenser coil where it gives up some of its heat. The
condenser fan moving air across the coil’s fi nned surface
facilitates the transfer of heat from the refrigerant to the
relatively cooler outdoor air.
When a suffi cient quantity of heat has been removed from
the refrigerant gas (vapor), the refrigerant will “condense” (i.e.
change to a liquid). Once the refrigerant has been condensed
(changed) to a liquid it is cooled even further by the air that
continues to fl ow across the condenser coil.
The RAC design determines at exactly what point (in the
condenser) the change of state (i.e. gas to a liquid) takes
place. In all cases, however, the refrigerant must be totally
condensed (changed) to a liquid before leaving the condenser
coil.
The refrigerant leaves the condenser coil through the liquid
line as a warm high pressure liquid. It next will pass through
the refrigerant drier (if so equipped). It is the function
of the drier to trap any moisture present in the system,
contaminants, and large particulate matter.
The liquid refrigerant next enters the metering device. The
metering device is a capillary tube. The purpose of the
metering device is to “meter” (i.e. control or measure) the
quantity of refrigerant entering the evaporator coil.
In the case of the capillary tube this is accomplished (by
design) through size (and length) of device, and the pressure
difference present across the device.
Since the evaporator coil is under a lower pressure (due to
the suction created by the compressor) than the liquid line,
REFRIGERATION SYSTEM SEQUENCE OF OPERATION
SEALED REFRIGERATION SYSTEM REPAIRS