How Does A/C Work?


Almost all car air conditioners operate the same. The refrigeration cycle works on the principle of latent heat vaporization or turning a liquid into a vapor. A compressor moves refrigerant through the system. For decades, air conditioners used CFC-12, often known as R-12. Then, in the early to mid-1990s, all vehicle manufacturers switched to the less dangerous HFC-134a (R-134a). When installing or diagnosing an A/C system, it helps to know how it works and what refrigerant it uses (look for a label on the compressor or evaporator unit). An overview of common hot rod air conditioning systems. Examine how the A/C system generally works.

What Makes Up an Automotive A/C System?

Consider the A/C system as a continuous loop separated at the compressor into high- and low-pressure sides. The compressor clutch compresses the low-pressure refrigerant gas into a high-pressure gas.

Condenser: The condenser is normally situated in front of the radiator. The condenser, like the cooling system radiator, removes heat from the high-pressure gas.

As the heat from the refrigerant is released into the air, the high-pressure gas transforms (condenses) into a high-pressure liquid.

The still-pressurized liquid then flows into the receiver-drier, which has a filter to remove debris and moisture from the refrigerant. Moisture and refrigerant can generate corrosive acid.

The purified liquid refrigerant travels through the A/C hoses into the car’s cabin, where it passes through a thermal expansion valve. The refrigerant vaporizes when the liquid’s high-pressure lowers.

The valve then directs the fine mist into the evaporator case under or behind the dash. The expansion valve or metering valve causes the refrigerant to evaporate as it enters the evaporator, absorbing heat.

A blower motor inside the evaporator case blows air through it. The heat is subsequently taken from the air and transferred to the refrigerant, allowing cool air to enter the cabin.

What Is An A/C Compressor?

The compressor circulates refrigerant throughout the A/C system. Most compressors are pistons-in-cylinder, with intake and discharge strokes for the refrigerant. The capacity of the compressor should be compared to the remainder of the system. Excessive pressure from a large compressor might reduce cooling and component life. An 8 to 9 cubic inch displacement compressor can efficiently cool large passenger compartments. The Sanden SD508 is the most frequent aftermarket compressor.


How Big Should the AC Condenser Be?

In an a/c system, the condenser’s efficiency is perhaps the most critical factor. Its performance determines the A/performance. C’s Aim for the largest and most efficient condenser that fits beneath the hood. Space is restricted and varies in specialized applications like street rods, therefore careful measuring is required. Because space is limited on pre-1950s rods, a high-efficiency aluminum condenser can aid. It doesn’t matter how big the condenser is, it will only operate as well as the airflow it receives. To prevent heat transfer from the radiator, always mount the condenser 1/8-inch in front of it.


What Does a Receiver-Drier Do?

Prevents moisture and impurities from entering the evaporator by filtering the refrigerant. Expansion valves only accept liquid refrigerant. The dryer contains desiccant material that absorbs moisture, so keep the shipping caps on until you’re ready to attach it to your new A/C system. The drier is usually positioned near the condenser, however, it can be placed anywhere in the system away from hot spots. A constant supply of fresh air ensures that the liquid refrigerant does not heat up and evaporate. Inlet and output sources or an arrow indicating flow direction are always marked on the dryer. Unless the unit is built for horizontal mounting, it should always be positioned vertically to keep liquid refrigerant away from the condenser.


Do I Need a Safety or Trinary Switch For My A/C?

The safety switch simply opens and closes the electrical circuit to the compressor. The safety switch closes the electrical circuit as long as the pressure in the high side line (between the condenser and evaporator) is safe. Pressure switches open or close the circuit to prevent the compressor from cycling. A binary switch shuts down a mechanical fan, but a trinary switch does more. The trinary switch is utilized with any electric fan. When high side pressures start to rise, the trinary switch activates the fan to move more air across the condenser. They can be installed anywhere in the high-pressure line between the condenser and evaporator. Some choose to hide the safety switch beneath the dash near the evaporator for a neat look. Alternatively, Speedway offers receiver-driers with a built-in binary switch.


What Does An Evaporator Coil In A Car Do?

The evaporator coil is a tiny radiator inside the evaporator box (HVAC stands for Heater, Vacuum, and Air Conditioning). It operates by transferring heat from the air to the refrigerant. The evaporator’s low-pressure liquid evaporates into a low-pressure gas when heated by the air. Because it’s tough to redesign a hot rod or muscle car’s dash around A/C components, the evaporator’s design can influence which unit to employ. Some solutions merge the evaporator and heater core to save space. There are two primary types of evaporators: under dash and in-dash, and the choice usually comes down to space. Today, many popular muscle vehicles and classic pickups have direct-fit A/C systems.


How Does The Expansion Valve In A/C Work?

The expansion valve controls the flow of refrigerant into the evaporator coil. Temperature-sensing bulbs and tubes measure the temperature at the evaporator’s outlet to control the flow of refrigerant. The evaporator’s warm outlet permits refrigerant to flow into the evaporator. The expansion valve restricts flow to the evaporator when the temperature at the evaporator’s outlet decreases. Avoids evaporator freezing, which affects cooling efficiency.