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An  undercharged  system  will  result  in  poor  performance  (low 

pressures, etc.) in both the heating and cooling cycle.

Whenever you service a unit with an under charge of refrigerant, 
always suspect a leak. The leak must be repaired before charging 

the unit.

To check for an undercharged system, turn the unit on, allow the 

compressor to run long enough to establish working pressures in 

the system (15 to 20 minutes).

During the cooling cycle you can listen carefully at the exit of the 
metering device into the evaporator; an intermittent hissing and 
gurgling sound indicates a low refrigerant charge. Intermittent 
frosting and thawing of the evaporator is another indication of a 

low charge, however, frosting and thawing can also be caused by 
insuffi cient air over the evaporator.

Checks for an undercharged system can be made at the compressor 

. If the compressor seems quieter than normal, it is an indication of 

a low refrigerant charge. A check of the amper age drawn by the 
compressor motor should show a lower reading. (Check the Unit 
Specifi cation.)  After the unit has run 10 to 15 minutes, check the 
gauge pressures.

Gauges connected to system with an under charge will have low 

head pressures and substantially low suction pressures.

Compressor amps will be near normal or higher. Noncondensables 
can also cause these symptoms. To confi rm, remove some of the 
charge, if conditions improve, system may be overcharged. If condi-

tions don’t improve, Noncondensables are indicated.

Whenever an overcharged system is indi cated, always make sure 

that the problem is not caused by air fl ow problems. Improper 

air fl ow over the evaporator coil may indicate some of the same 
symptoms as an overcharged system.

An over charge can cause the compressor to fail, since it would 

be “slugged” with liquid refrigerant.

The charge for any system is critical. When the compressor is noisy, 

suspect an overcharge, when you are sure that the air quantity over 

the evaporator coil is correct. Icing of the evapora tor will not be 

encountered because the refriger ant will boil later if at all. Gauges 
connected  to  system  will  usually  have  higher  head  pressure 
(depending upon amount of overcharge). Suction pressure should 

be slightly higher.

Refrigerant Charging