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How Car AC Systems Work & How To Recharge Your AC System

Date: 09/23/2017

How Does it Work

A car is an almost airtight, metal, plastic and glass box. It absorbs and retains outside heat and moisture without letting out the inside heat and moisture and if the outside weather isn’t bad enough, it is attached to a hunk of metal that constantly creates countless fiery explosions. So cars tend to get hot.

Air Conditioners therefore, are indispensable but how do they work?

The most important ingredient here is the refrigerant. This absorbs the heat from the air entering the cabin making it cool. This is a gas, most probably Freon R134a. Unlike its predecessor it has little impact on the ozone layer and has a boiling temperature of −15.34 F or −26.3 C. This fact becomes important later.

This refrigerant is circulated throughout the AC circuit. First this gas is sent into the compressor. It is driven by the engine itself with the help of an engine belt. It comes in at low pressure and temperature and is compressed to high pressure and temperature. It is then sent into the condenser to cool off. The condenser is at the front of the car, with the radiator for better air flow. Air is captured by a fan or by the forward movement of the car itself. This air condenses the high temperature refrigerant gas to liquid form. The air then gets sent to a receiver dryer through a filter (to remove any harmful debris) and a desiccant (to remove any water). (Any water mixed with the refrigerant could freeze in the evaporator and damage it) Next, it goes into either an expansion valve or in some cars, an orifice tube. This controls the flow of the refrigerant into the evaporator. As the liquid expands in the expansion valve, it loses speed and pressure and just as the gas gained temperature under pressure, it loses that temperature when the pressure drops. Despite this drop, the refrigerant is still in a liquid phase as it enters the evaporator.
This very cold refrigerant is what cools the air entering into the cabin. A cabin fan blows air from the front of the car onto the evaporator, which along with the expansion valve, sits under the dash. These cooled fins absorb heat from the air, and the cooled air is sent into the cabin through the vents. The refrigerant however, has absorbed all the heat from the ambient air. Because of its low boiling point (as mentioned above), this heat literally boils it- i.e. it turns into a low pressure and temperature gas. If the car uses an orifice tube, it goes into an accumulator, which removes any remaining liquid from entering the compressor. After this, it goes into the compressor again and the cycle repeats itself.

Recharging the AC

Because of modern engineering, ACs have become very reliable. For most people the only maintenance issue likely to come up, would be a need to recharge the refrigerant level. Many companies provide kits through which this becomes a DIY task. They may even come equipped with a reusable pressure gauge connected to a dispenser tube and a temperature indicator. Some even have additives that seal slow leaks by causing the O Rings and gaskets to swell up. However if your system has leaks, it is best to get it fixed by a professional at Spencer Auto Repair.

Just put the AC on max and ensure the compressor is running and that the clutch engages. Then find the low pressure port to which you can connect the dispenser of the refrigerant. This port is often marked with an L on the top. Then connect the pressure gauge to the port. Listen for the reassuring click to ensure it fits. This next part is a bit tricky you must ensure that the bottle pressure is in the safe zone at all times to avoid overcharging. Twist the outer ring of the gauge to match the outside temperature. The pressure at this temperature should lie within the safe zone, as marked on the pressure gauge. Once this is ensured, you can detach the dispenser tube, attach the bottle and start recharging. Keep the bottle upright and keep it turning sideways by 90 degrees and checking the pressure gauge every few seconds. Charge till the needle falls between the marked pressure ratings or the suggested pressure and replace the cap. If you end up overcharging then you’ll have to take it to a professional, so be careful.

If after you recharged the systems the care is still not blowing cold air you might have a problem in another part of the system and you should take it to your local mechanic to have it checked. If you are in the Mesa Az area, Spencer Auto Repair can fix any AC system for all makes and models.