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Uncool and uncomfortable

Question : I SUSPECT my 1985 Nissan 130Y may have an electrical problem.

After an extended run, the air conditioning system cuts off and cooling does not resume until it has been switched off for at least 15 minutes. I have consulted at least three air-con specialists but none have been able to solve the problem.

Answer : THE air conditioner of a car works on the principle of a refrigerator, removing heat from the air within the passenger cabin, and discharging the heat into the atmosphere.

A typical air conditioning system consists of a compressor situated between two radiator coils. The compressor pressurises a gas (freon, a family of gases that contain hydrogen, carbon, chlorine and fluorine), transforming it from a gaseous to a liquid state.

The liquid is forced through an orifice into a cooling coil (located in the passenger compartment), where it evaporates. The evaporating fluid absorbs heat from the atmosphere (cabin). The gas is then transported out of the passenger compartment to another cooling coil located in the engine compartment where excess heat is discharged to the atmosphere.

The cycle is repeated and the gas is re-compressed. There are many reasons why an air conditioner can stop working, and one of the most common is that the compressor fails to engage (compress).

A safety switch located along the air-conditioning lines switches the compressor off should the system pressure rise or fall below pre-set safety levels. Although these switches are relatively reliable, they are liable to occasional failure, but replacements are relatively cheap.

Alternatively, the switch could be switching the compressor off because the system pressure has risen beyond the upper safe working limit. This is either because the system has been overfilled with gas or the electrical cooling fan has failed, resulting in excessive high system temperatures and consequently exces- sive pressures.

On the other hand, if there is a leak in the system and system pressure falls below a lower safe limit, the compressor must be prevented from running in order to prevent damage to compressor components. An air-conditioning system specialist would be able to measure if system pressure is causing your problem.

The last possible cause is the failure of the thermostat or the "anti-frost switch" (if available). This prevents excessive cooling and icing of the cooling coil.

A build-up of moisture around the cooling coil reduces airflow through the coil resulting in reduced airflow, hence reduced cooling efficiency.

Thermostats and anti-frost switches are relative cheap components to replace, and a specialist should be able to determine if they have failed.


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