Know Your Car AC System Part 1

Preamble
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 ACs 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.

How to get the best out of your Car A/C.
Let us consider the M-800 System, being most omni-present and ‘Edgy’ by design, by virtue of the Engine itself being < 50 Bhp. This exercise can be divided into two parts:

A. Your Garage.

(i) It should check whether the System is Healthy, by way of Suction/Discharge Pressures, Internal or External Component Blockages, ‘Pressure equalisation’ times on Switching Off and Cabin Grill Temperature.

(ii) On M800 ‘Retrofits’, check whether a 120Watts Radiator Fan is provided, by replacing the ‘Standard’ 80-Watt one.

(iii) Ensure proper Foam sealing on all the four sides between the Radiator and the Condenser, between the Exhaust Manifold and the Condenser (behind the Bumper). This is the most neglected area.

(iv) Existence of a ‘Heat Shield’ around the Compressor discharge pipe and the Condenser in an M800, as provided in an ‘OE’ fitment. This again is generally thrown away by mechanics right during the first service of a new car, thinking that it serves no useful purpose. If it were so, it won’t be provided by the Manufacturer in the first place and be subsequently priced as an MGP/SGP Spare costing over Rs: 350/-!

(v) Whether the Radiator Fan comes on and stays on even when the Radiator Thermo Switch cuts in. Approach in reverse sequence especially for the Retrofits.

(vi) Check all parameters of the Engine Tune, such as Idle RPM/CO, FICD RPM (1050), Ignition Timing including satisfactory working of Centrifugal and Vacuum Advance features, Dwell angle and its stability up to 4000RPM, Spark Plug condition and Gap, Air Cleaner/Petrol Filter Cleanliness, Carburetor II Butterfly in good working order, Engine Valve Clearances and Timing (if suspect).

(vii) Wheel alignment, Engine Compression/Power balance (if suspect), Radiator/Condenser Cleanliness (inside/out), condition of Radiator Cap/Thermo valve (Change if suspect). In our Dusty conditions, these two have to be pressure washed every 2-months from both sides.

(viii) Correctness of Dash Board Temp Gauge vis-a-vis digital thermometer in the Radiator neck, Radiator Fan coming on without A/C around 85*C to 90*C, full closing of Fresh Air Damper in ‘Recirc’ mode and proper alignment in ‘Full Forward’ Mode.

B. Yourself

(i) Do read and follow the Owner’s Manual on the Car A/C usage.

(ii) Maintain the recommended Tyre pressures.

(iii) Always drive in a gear one step lower with A/C on, than what is recommended for normal driving.

(iv) Ensure that the ‘Recirc’ flap is always closed and avoid driving in our dusty conditions with Fresh Air flap open, as it deposits dirt on the cooling coil, thus making it less and less efficient.

(v) Always get your A/C checked out at a competent and reliable Garage at the beginning of a season.

(vi) Check frequently the ‘free-rolling’ of your car, to guard against ’sticky brakes’. This can be very easily done when coming to a stop, say at traffic lights. Just let go of the brakes when the car is about to stop and shift to neutral. The car should continue to move forward without any noticeable feeling of a ‘drag’. Don’t forget to engage the hand brake when you come to a stop!

(vii) Last but not the least, it’s of utmost importance to switch on a Car AC atleast once a week even in Winter times and let it cut-off on its Thermostat once or twice - to keep the System internals well lubricated. This is coz the lube oil of an AC System moves along with the AC Gas !

C. What can go wrong!
Perhaps the most common ‘complaint’ of most Car Owners is that either the AC is not cooling well enough OR when they use it, the engine over-heats.

Here are some tips to equip you against being taken for a ride by who so ever you choose to have it fixed by:

i) Not Cooling enough :

The main reasons for this, assuming that your System is physically in good shape, can be - a) Under OR over Gas Charge, b) Dirt-clogged front-end AC Condenser, c) Choked ‘Receiver-Drier’, d) Faulty ‘Expansion-Valve’, e) A dirt-clogged ‘Cooling-Coil’, f) Faulty ‘Anti-Frost’ Thermostat on the Cooling Coil, g) Loose AC Compressor Drive Belt OR its faulty ‘Clutch’.

ii) Engine Over-heating :

Likewise - a) Dirt-Clogged Engine-Radiator, b) Engine ‘Out of Tune’, c) Jammed II-Butterfly - especially in Carb type M800’s, d) Driving in a gear higher than what the engine demands, e) ‘FICD’ engine speed being much higher than recommended, f) Car not ‘free rolling’ enough for whatever reason - as covered above.

Conclusion
Once you have got the hang of it as to what makes it tick and keeps it ticking, there is no reason why it should not deliver satisfactory performance even through the peak of our North Indian summer. I have personally driven an M800 through Rajasthan in the month of May with outside temperature being 48*C, Cruising speeds up to 100kph, Cabin Temp. around 25*C, and the Engine Temp. not crossing the halfway mark!