Condenser with airflow restriction - external
Usually from insects or grass seeds clogging the finning. However, airflow restriction may also be caused by insect screens, oil coolers and other obstructions which restrict airflow.
Condenser with airflow deficiency
Insufficient airflow due to electric or viscous fan(s) not operating correctly, low voltage, the fan incorrectly positioned in shroud, or the condenser placed too far from the radiator.
Condenser with internal blockage
May be caused by particles from another component such as a failed compressor or other component affected by internal corrosion from moisture due to contaminated oil/refrigerant. Internal condenser blockages are usually only partial, in which case vapour is fed to the receiver-drier and TX valve, with resultant reduced performance. A special note as to parallel and sub-cool condensers: they cannot be flushed clean as flushing solvent will only take the path of least restriction, and will not clean the whole condenser. Note too that a parallel or sub-cool condenser can be up to two thirds blocked without showing any signs of flow restriction. To be sure, in the event of a full compressor failure on a system with a parallel flow or sub-cool condenser, it must be replaced.
Condenser with leaks - inherent
Rare in good quality condensers. Can occur from age, physical damage, or corrosion. Core leaks are common in poor quality condensers, often aggravated by high head pressure in/from the compressor.
Condenser with leaks - fittings
Usually caused by bad installation techniques such as re-using old O-rings, failure to lubricate fittings or failure to line-up fittings prior to tightening.
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.
Example
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