With more than a half million air being installed on cars annually it’s a foregone conclusion that there will need to be a lot more attention paid to the cooling system and engine efficiency. And unless there is a better understanding of how air conditioners work a lot of motorists are going to be mighty hot and bothered over their summer cooling.
Fortunately the breakthrough is conveniently afforded by a tour of inspection of the kitchen’s electrical refrigerator. Here we find the same basic plan as in the car air conditioner except for the pump or compressor which is driven by the engine of the car instead of by an electric motor. Here, briefly, are the essential steps in car cooling:
The compressor picks up the heated re-frigerant vapor from the system and discharges it into a condenser which is located just ahead of the engine’s radiator. Immediately, the vapor goes into liquid form, throwing off heat into the passing air currents. From here the liquid refrigerant goes to the receiver, and then through an expansion valve into the evaporator where it boils and goes back into vapor. The process of turning the liquid into a gas cools the evaporator and the air surrounding it. Finally, the vapor is drawn back into the inlet of the compressor to start the cycle all again.
Ice cools by absorbing heat as it melts. A refrigerant cools by absorbing heat during its process of changing from liquid form to vapor. Keep in mind also that transfer of temperature always is from a warm object to one that is cooler.
All this seems simple enough, but the problem is the fact that in an automobile we have to saddle all load on top of the car’s cooling system at the very time when things are already at the sizzling point. Putting it frankly, the air conditioner is no better than the efficiency of the car’s cooling system. Let the car develop trouble and the chances are that there will at least be a temporary halt in cooling comfort.
The air conditioner usually is independent of the car’s ventilating and heating system. There’s always a blower wheel or a fan designed to move air across the evaporator coils and into the car’s body. Ducts are provided for even distribution of cooled air when the system is factory installed; and if it is one added to the car there would be louvers to provide for variations in aiming of cold air flow. Systems vary somewhat in their details. You may, for instance, find a small between the compressor and the condenser.
Compressors may be of the rotary or the reciprocating type. There may be a fusible plug at the bottom of the receiver which will
wiallow refrigerant to escape before its temperature exceeds 231 degrees Fahrenheit.
After leaving the condenser, the liquid refrigerant is forced into the receiver (a reservoir) so that there is always a sufficient supply to be fed to, and then through, the evaporator. This receiver is also a dehydrator for removing all traces of moisture.
Obviously the compressor must be equipped with a means of disengagement when no cooling is needed, or if cooling becomes excessive while the system is in operation. A magnetic clutch with thermostatic switch control is the popular way of handling this. The compressor also has a reservoir for its own lubrication, and there is the matter of its drive belt which usually should be adjusted for 1/2 -inch deflection midway between the compressor and the pulley from which the drive is received.
Not only does the compressor rob the engine of some of its power, but heat given off by the condenser passes through the engine’s radiator core at the very time the latter needs cooler air. Many cars with automatic transmissions also have an oil cooler at the bottom of the engine radiator so that the transmission’s efficiency may be impaired by operation of the air conditioner. That everything works out as well as it does is a tribute to the skill of the car makers and the air conllditioner manufac- turers. But no system wioperate satisfactorily unless certain rules are followed.
If you keep the conditioner on Manual for continuous operation on a very humid daythe evaporator will ice up, and that will
wicut off air flow through this vital unit of the system. Under such conditions it is better to set the conditioner for Automatic operation.
On some cars the heater core is close to the evaporator and the temperature of thecold air entering the driving compartment is adjusted by the amount of coolant passing through the core of the heater. Here it is possible to freeze the heater’s coolant unless ethylene glycol antifreeze is used in summer. In other words, antifreeze should be used in such cases, not to raise the boiling point of the engine’s coolant, but to protect the heater core against freezing!
Owners of cars with air-cooled engines can buy compact air conditioners. These can be installed without altering the engine’s cover or making body modifications.