|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.