Condenser diagnosis tips

Apart from leaks, which are usually visible due to oily patches, most condenser problems are indicated by high head pressure. In a condenser, all types of blockages or restrictions, internal or external, will increase head pressure and cause a drop in performance.

Internal blockages can usually be detected by feeling the condenser for cool spots. Where the refrigerant is under pressure it will be hot, where the pressure drops it will be cool. In the case of a partial blockage the low pressure side may be quite cold, even though surroundings are hot. A good check for efficient condenser operation is the temperature drop across the condenser. A drop of about 20°c from the temperature at the inlet to the temperature at the outlet is normal.

Condenser - calculation of capacity

Calculation of the capacity of a condenser in relation to the rest of the system depends on many factors. However, it is generally accepted that the capacity of the condenser should be at least 40 - 50% higher than the capacity of the evaporator. The calculated capacity of a condenser does not indicate the cooling capacity of the system.

Condenser - superheat & sub-cooling

Normal superheat and sub-cooling is essential if the system is to operate at peak efficiency. While a number of factors have an effect (such as the superheat setting of the TX valve), in simple terms the compressor increases the pressure (and therefore the temperature) of the refrigerant to a point above its condensation temperature. This is called superheat. The condenser dissipates some of the heat and the refrigerant liquefies (condenses). In an efficient condenser there is a further cooling of the refrigerant below its condensing temperature and this is known as sub-cooling. 

Vehicle: Medium Sedan
RPM: 1500
Ambient temperature: 29°C
System head pressure: 1500 KPA
System head Temperature: 58°C (from temperature pressure chart or gauge)
Condenser inlet: 73°C
Condenser outlet: 50°C
Therefore Temperature: Drop across cond. 73 - 50 = 23°C
Superheat: 73 - 58 = 15°C
Sub-cooling: 58 - 50 = 8°C