Does your car idle rough or the speed cycle up and down. You probably have a bad idle air control valve. The only purpose of the idle air control valve is to keep the engine’s idle smooth. The engine’s computer gives the idle air control valve the feedback it needs to hold a constant rpm. The idle will be around 1000 rpm’s when not in gear and around 800 rpm’s in gear. This iac valve is on a Nissan Maxima and is similar to most idle air control valves.
An air temperature sensor is used on fuel injected engines. The purpose of an air temperature sensor is to help the computer calculate air density. A change in temperature changes the resistance in the sensor. Simply stated, the higher the air temperature gets the less dense the air becomes. As the air becomes less dense the computer knows that it needs to lessen the fuel flow. If the fuel flow was not changed the engine would become rich, possibly losing power and consuming more fuel. The temp sender is generally located in the air inlet tube or the air box. The wire running to the sensor can be disconnected then the sensor can be unscrewed and replaced. Some aftermarket companies trick this sensor with a resistor (false temp reading) to make the engine run richer. If a engine has been tuned lean this trickery can show mild power gains.
Auto air conditioning can easily be changed from old R-12 to new R-134 refrigerant. The new style R-134 refrigerant can be used in R-12 systems as long as the oil is included with the installation of the new refrigerant. No new seals or any other components should need to be replaced. Your car’s system should be completely empty of the old R-12, which is supposed to be contained and removed by a certified refrigerant technician. When doing anything with ac you should first understand that there are two sides of the system. The high pressure side will be the side with the smaller diameter lines, this side is very high pressure and should be avoided. The low pressure side will have the larger diameter lines and will have the condenser. The condenser looks like an aluminum canister of about 4″ in diameter and appx. 6″ long. The fill port will probably have a plastic cap on it. The port is a valve that looks like a air fill on your car tires. You will need a kit composed of an adapter and the hose used to fill the system with. Some types of cars need different adapters.