Friedrich CP18N30 Manual Do Utilizador

8

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 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 

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.

Refrigeration System Sequence of Operation