Friedrich SQ08N10 Manual De Usuario

A good understanding of the basic operation of the 
refrigeration system is essential for the service technician. 
Without this understanding, accurate troubleshooting of 
UHIULJHUDWLRQV\VWHPSUREOHPVZLOOEHPRUHGLI¿FXOWDQGWLPH
consuming, if not (in some cases) entirely impossible. The 
refrigeration system uses four basic principles (laws) in its 
operation they are as follows:  

³+HDWDOZD\VÀRZVIURPDZDUPHUERG\WRDFRROHUERG\´

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 
KHDW7KHFRQGHQVHUIDQPRYLQJDLUDFURVVWKHFRLO¶V¿QQHG
surface facilitates the transfer of heat from the refrigerant to 
the relatively cooler outdoor air. 
 
:KHQDVXI¿FLHQWTXDQWLW\RIKHDWKDVEHHQUHPRYHGIURP
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 
WKHDLUWKDWFRQWLQXHVWRÀRZDFURVVWKHFRQGHQVHUFRLO

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 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 
LQGRRUDLUDFURVVWKH¿QQHGVXUIDFHRIWKHHYDSRUDWRUFRLO
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 
KHDWHGHYHQIXUWKHUE\WKHDLUWKDWFRQWLQXHVWRÀRZDFURVV
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.  

REFRIGERATION SEQUENCE OF OPERATION

 

26