Friedrich WS10B10A-C ユーザーズマニュアル

11

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 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.

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 flows 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, 
the liquid refrigerant leaves the metering device entering 

REFRIGERATION SYSTEM SEQUENCE OF OPERATION