Cooling Guide - A Hot Topic Part I

Of all the street rod topics we deal with, the one that generates the most questions is cooling-all sorts of cooling. It's a big subject that can include everything from the parts under the sheetmetal to the passengers who ride inside.

To address a topic this large, we put together a series of the most frequently asked questions to present to experts in their various areas of expertise. This month, we begin with air conditioning and radiators-two subjects that are near and dear to most street rodders. In future issues, we'll deal with fans, fan controls, water pumps, insulation, and all the other hot topics concerning cooling.

Air Conditioning
1. How is the size of an air conditioner evaporator determined?

Hot Rod Air
The basic concept is to install the largest-capacity unit possible. We match evaporator coil to blower assembly and case design for maximum performance. Several factors also come into play. First and foremost is the size of the interior you are trying to cool (a coupe will require less Btus than a four-door sedan). The second factor would be the amount of physical space behind the dash-in some cases, you may need to have the evaporator hang down below the dash area a bit if space is tight. Keep in mind that when the system is on high and working to its maximum capacity-say, on a 100-degree day-it is easier to turn it down than to turn it up.

Southern Air
Our first heat and air unit was a mere 16 inches wide and 7 1/2 inches deep, and we soon learned that this fit tons of small rods, such as A models and most '30s cars. This unit would heat and cool these cars, but when it came to the '40s sedans, it was a little small so we began matching units to the size of the vehicle. We dyno-test all of our new units before we put them into production; so, if the customer gives us the car make and model, we have a unit for it based on the inside cubic feet of space in that car.

Vintage Air
We always recommend selecting the largest-capacity evaporator that will fit in the customer's vehicle. You can turn down the fan and adjust the temperature on a system if you get too cool inside your car, but you cannot make a unit that is too small cool a large area. Think about the climate-control system in the early stages of car construction. We manufacture mock-up units to not only determine fit, but to make it easy to fine-tune mounting brackets before hanging the actual unit. Many of our dealers loan these units for a nominal fee.

2. How is the size of the condenser determined?

Hot Rod Air
Condenser size is very simple: The larger the better; fill as much of the radiator core size as possible. You cannot oversize a typical street rod condenser. You should have a minimum of 230 square inches of condenser.

Southern Air
The size of the condenser is determined by the core size of the radiators. We use only parallel-flow condensers, and the salesperson will ask the year and model of the car when the kit is ordered. We will then supply a condenser that will fit.

Vintage Air
All of the components must be sized properly and matched. The evaporator absorbs the heat from inside the vehicle, and the condenser dissipates the heat to the air. We recommend selecting the largest condenser that will fit within the dimensions of the radiator core, and the use of parallel-flow condensers.

3. What engine/cooling system modifications are necessary to add air conditioning?

Hot Rod Air
Most important is making sure the motor is positioned in the framerails so you can run a good-size fan. Keep in mind that the newer blocks are designed to run warmer temperatures than earlier motors (so don't be alarmed when you see 210 to 220 degrees

Southern Air
In a nutshell, you need a really good radiator fan, thermostat, and medium-volume water pump. Stock-size pulleys are your best bet, as GM and Ford have better engineers than any of the aftermarket sellers. I have an aluminum, dual-row radiator in my '46 woodie with 1.50 tubes and a 430hp Vortec 350. It will not overheat, but I also have one of our 16-inch, 225-watt fans with our adjustable thermostat.

Vintage Air
If an engine-cooling system has adequate components and is operating at its proper efficiency, no modifications should be necessary just because air conditioning is added to a vehicle. If an engine-driven fan is on the vehicle, we always recommend a shroud to maximize the efficiency of the fan. If a customer is using an electric fan as his primary cooling fan, we strongly recommend the addition of a trinary safety switch, which allows A/C system pressure to engage the fan in conjunction with and independent from engine temperature.

4. Do you recommend mechanical or electric fans with air conditioning?

Hot Rod Air
Engine-driven fans with a shroud will give you the most consistent cooling. Depending on the vehicle, if you can also run a pusher fan as a secondary fan, this will increase the air-conditioning performance at slow speeds. A second scenario is that anything less than a 17-inch engine-driven fan usually does not have the cfm to be used as a primary cooling fan; at that point, you should look at using a 14- to 16-inch electric fan and shroud combination. With air conditioning, you will need at least 2,500 cfm of airflow.

Southern Air
We highly recommend the six-blade Flex-a-lite stainless with our radiator shroud; however, this combination doesn't fit all cars, so get the best and biggest fan you can on the car. For instance, '33-34 Fords don't have much room between the water pump and the radiator, but one really good 12-inch fan and one 10-inch will fit on the grille side. If you're building a chassis, set it up with the motor back far enough to make room for a good fan.

Vintage Air
The key is airflow, and it doesn't matter if you achieve the airflow with an engine-driven fan or an electric fan. When using a mechanical fan, we like to see a minimum of a five- or six-blade fan with 2 inches of pitch. Be careful when selecting an electric fan as the primary cooling fan-many just don't have the capacity. We recommend selecting a fan with at least 2,600 cfm when the vehicle is equipped with air conditioning. Both fans will benefit from a good shroud and a smooth air path.

5. What interior modifications do you recommend when adding air conditioning (tinted windows, insulation, etc.)?

Hot Rod Air
Keep one thing in mind-air-conditioning systems do not make cold air; they remove the heat that is in the air, so you must seal all holes and door seals to keep the forced air from entering the interior. Insulate any surface in the interior, doors, firewall, headliner, upper cowl, kick panels, etc. If there is a surface, insulate it. This will also give you a quieter ride. Tinted windows, especially in the South and in warmer climates, will help-nothing more so than purchasing an evaporator large enough for your vehicle cab.

Southern Air
Tinted windows help, but nothing beats door seals and floor and door insulation. If the doors are not sealed, it creates a vacuum cleaner effect and out goes your cool air.

Vintage Air
The single most important factor in improving the efficiency of a climate-control system is how well the vehicle is sealed and insulated. You must keep the engine heat and outside heat load out of the interior of the vehicle. Tinted windows help reflect the heat soak from the sun, and this helps the air conditioner cool the vehicle more efficiently as well. Proper weatherstrip and door/ glass seals will also help isolate the interior and lessen the load on the A/C system. Be sure to seal any holes in the firewall, along with the clutch and brake pedals.

6. Do you offer air-conditioning compressor mounting brackets?

Hot Rod Air
Yes, for just about any motor out there. If there is not a specific bracket available, we also offer a universal bracket that gives the customer a cradle to start with and all they will need to do is build a baseplate for attaching it to the motor.

Southern Air
We carry a full line of Alan Grove steel brackets and our exclusive polished stainless steel brackets. We also make many billet aluminum brackets and carry all of Street & Performance LS-series mounts.

Vintage Air
We offer a wide variety of compressor mounting brackets, ranging from basic steel assemblies to our Front Runner drive systems that package all engine accessories.