Getting a grip on air conditioning
Words & Photos: Todd Ryden
Years ago, rods were basic builds with no accessories, bells, or whistles. They were meant to either be quick or look cool, and sometimes both. As time and technology have progressed, many builds have become more refined with creature comforts for a more comfortable drive.
One such accessory that has become the norm is air conditioning — and with good reason. Southern states that drip with humidity through the summer make it unbearable to cruise, and the Midwest reaps some pretty serious heat during prime cruise months, as well. Remember, an A/C system not only cools the air, but it removes the moisture to keep your cabin cool and dry.
It’s no surprise Vintage Air, the original street rod A/C company, was started in one of the hottest and most humid cities in the country — San Antonio, Texas. If you could develop an A/C system that keeps a street rod cool in San Antonio, then you’re pretty well set for the rest of the country!
Vintage Air knows what it takes to make a car stay cool on the inside, but for many of us, understanding what exactly is going on inside those hoses and tubes is a mystery. Automotive air conditioning may seem tricky to understand at first, so let’s take a look inside to get a better grip on keeping cool.
The best thing to compare the actions and flow of refrigerant is to think back to middle school and the hydrologic cycle. As it’s heated, water evaporates from a liquid to a gas. Then as it cools, it condenses back into liquid form again. And if you were awake for any physics courses, recall that heat always transfers from a hot object to a cool object. Never the other way around.
The A/C system does the same basic thing with refrigerant, as you can see in the diagram. Refrigerant enters the compressor as a cool, low-pressure gas and exits as a hotter, high-pressure gas before reaching the condenser.
The heat of the high pressure refrigerant is transferred to the ambient outside air that is also flowing across the fins of the condenser. This cools the refrigerant, allowing it to condense into a high-pressure liquid state. It then flows through a receiver-drier, which removes any moisture that is in the system and separates any remaining gas bubbles from the liquid. It also serves as a storage vessel for the liquid refrigerant.
After the refrigerant leaves the receiver-drier, it flows through the expansion valve where a variable orifice controls refrigerant flow. When the refrigerant passes through the expansion valve, the pressure of the refrigerant drops significantly, creating a spray of refrigerant droplets, which absorb large amounts of heat as they change (again) from liquid back to gas.
Inside the car, the blower motor pushes hot cabin air through the evaporator (a heat exchanger) where heat and moisture is removed as it passes over the cooling fins of the evaporator. By absorbing the heat from the air, the refrigerant returns to a low-pressure gas state and is routed toward the compressor for another cycle.
That is simply the flow of the refrigerant and how the air is cooled. There’s a lot more to maintaining a consistent cool temperature over millions of cycles in your rod: the size and shape of the two heat exchangers (the evaporator and condenser), the compressor, switches to monitor the pressures and keep things safe, a receiver-dryer, and even the duct work and routing of the cooled air.
All of these things need to be designed to work together as a complete system to keep you cool. If you have any questions about removing heat from your rod, give Vintage Air a call. They’re always cool to talk with!
COOL CHECK LIST
As a rule of thumb, Vintage Air would like to see 36° to 46° out of the center ducts while cruising at 1,500 to 2,000 rpm. In many cases, the air conditioning system is functioning exactly as it was designed to do, but other things on the car are not helping the cause to keep you cool. Be sure to check and consider several of these areas of your rod as well.
Fan Shroud: Do you have a fan shroud? A shroud will not only help cool your engine temperature, it will also help the fan pull air through the entire core of the radiator and condenser to promote improved air conditioning. This is especially important at idle and low speeds.
Size Matters: Try to fit the largest evaporator possible under your dash. A kit to cool a station wagon needs more evaporator capacity than that of a five-window Deuce! As for the condenser, Vintage Air recommends at least 300 square inches of face area on a parallel flow condenser.
Insulate and Seal the Cabin: The more hot air you can keep out, the cooler the air is going to stay inside. Using insulation on the roof and floor will make a big difference. Also be sure any holes in the firewall and floor are sealed.
Heater Control Valve: Make sure the heater control valve is installed on the correct hose and is in the right position for the flow of coolant. If not, hot engine coolant circulates through the heater core, reducing the effectiveness of the evaporator and the cool air.
Vintage Air • 800-862-6658