It’s
that time of the year when Car AC’s are just about being switched
in – even in North India. They perhaps never got switched off ‘down
south’ of Nagpur!
Considering the fact that most motorists face problems with their Car
AC’s sooner than later, it’s worthwhile to get the hang of
it all – coz ignorance in such matters can cost one dear –
in more ways than one.
The
System
All Car A/C Systems are basically similar, with a cooling capacity of
almost
1-1.5 tons (!), in the sense that they essentially comprise:
1)
An Engine Driven ‘Compressor’ with an ‘Electro-magnetic’
Clutch. The Compressor Capacity is designated in ‘CCs’,
like the Engine. 80 to 120 CCs being the most popular ratings for passenger
Cars of the types on our roads. The ‘Refrigerant’ used so
far was ‘R-12’ of the ‘CFC’ family of gases
but is now progressively replaced by ‘R-134A’, a ‘NON-CFC’,
for environmental considerations.
2) A Grill-front mounted ‘Condenser’, cooled
either by a common (Radiator) fan or a ’Dedicated’ fan of
its own. For example Maruti 800 and Zen/Esteem - respectively. The latter
is a superior and hence a more efficient but naturally a more expensive
system.
3) This is followed by a ‘Receiver-Drier’,
mounted somewhere in the Engine Compartment. Its purpose is to control
and ‘Purify’ flow of the Refrigerant to the cooling coil,
under various operating conditions.
4) A ‘Cooling Coil’ with a multi-speed
Blower mounted in the Passenger Compartment, generally inside the Dashboard.
This unit has two additional and vital parts viz. (a) An ‘Expansion
Valve’ and (b) a ‘Thermostat’. The latter can be a
‘Bellows’ type like in the pre/EU-I M-800s or ‘Electronic’,
as in the Zen/Esteem and some others. All Mpfi Cars today have the Electronic
one only. Larger vehicles like the Tata Safari have two such units,
one up front and the other at the rear, to cool the entire passenger
area effectively.
5) The ‘Expansion Valve’ regulates the
quantity of gas flow to the Cooling Coil (also called the ‘Evaporator’),
depending upon the ‘Heat Load’ on it and the ‘Thermostat’
prevents ice formation on the cooling coil, which not only affects the
cooling efficiency but if allowed to happen, can also damage the system.
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