The Basics of Performance Air Conditioning

1.  Main purpose of air conditioning is to remove heat and humidity from inside the vehicle.

2.  How the system works.

Refrigerant absorbs heat as it changes states from liquid to gas in the evaporator and

dissipates heat as it changes from gas to liquid in condenser.

*Heat is absorbed through evaporation, dissipated through condensation.

*Refrigerant changes from high-pressure gas to high pressure liquid in the condenser.

 It then changes from a low pressure liquid to a low-pressure gas in the evaporator.

3.  List of basic air conditioning components and purpose.

             The evaporator absorbs heat/humidity – Expansion valve regulates flow of

              refrigerant.

                 Compressor – pumps refrigerant through system.

                 Condenser – cools refrigerant to induce change from gas to liquid.

             Receiver/Drier – filters particulates from refrigerant and removes moisture.

*Safety switches

             a. Binary - High (406 PSI) and Low (30 PSI) pressure protection

             b. Trinary - High (406 PSI) and Low (30 PSI) pressure plus an electric fan

            engagement signal  at 254 PSI (on high pressure side)

*Thermostat Switch - adjusts compressor cycle time.

             (Indirect temperature control)

4.            Refrigerants:

CFC-12  -  R-134a  -  blends/replacements - Vintage Air DOES NOT

             recommend blends.  Nor does Sanden or any other major A/C component
 
             manufacturers.  R-134a is a more efficient absorber and carrier of heat, which

            means it takes more efficient components to get the same heat transfer as we

            are used to from  R-12.      

-134a molecules smaller – require “O” ring fittings and barrier hose must be crimp

              connections (Bead Lock Recommended), no clamps.

-Newer style refrigerant hose has a nylon type inner core within the rubber hose.

General building and installation tips

           Consider air conditioning for your project very early in planning/building phase.

 - Mount engine far enough back to allow for condenser, fan, shroud and radiator.

- Use largest evaporator and condenser possible.

-Seal and insulate cabin area including floor, cowl and above evaporator.

-Install evaporator in dash/cowl area first, and position other components around it.

     Mounting compressor:

-Do not distort compressor body when mounting. (May cause oil leak)

-Minimum “Grade 5” bolts & sturdy, supportive bracket.

-Align pulleys well!

- At least 1/3” belt wrap – belt should contact/drive sides of pulley.

   (Should not bottom out in groove)

-R134a oil - PAG 100. (100 is the viscosity designation) Sanden’s equivalent is

              SP-20 oil

-90° maximum "clocking" to retain oil on Sanden SD508 Compressors.

-Clutch air gap -  .016 - .031

     Drier:

-Mount upright in airflow or cool area. (May be mounted inside vehicle.)

-Drier/safety switch combination convenient way to package safety switch.

     Condenser:

-In front of radiator up to 3/16” gap - do not place against radiator.

-1-1/4 volume of evaporator coil. (in³)

-Parallel flow condenser has 25% more capacity than same size tube & fin.

-Under car condenser not recommended for 134a as a primary condenser

Remember – temperature differential induces heat transfer. Air under car is

much warmer and more stagnant than clean air coming at front of car.

     Evaporator:

-Size evaporator to car – always try to package the largest evaporator possible.

-Mount solid, level – pay attention to drain hole and tube!

   *Seal and insulate car!!  Hot air coming in will hurt the best cooling A/C system.

 -Stretch duct hose to eliminate “ribbing,” reduce turbulence.  Route duct hose with

  smooth,  gentle bends.  Try not to kink or crush.

-Never cap un-used evaporator outlets!  Creates cavitation and “cold spots” in coil

and may lead to evaporator freeze up. Let it flow out somewhere.

-Do not completely seal off under dash (air can not re-circulate to blower).

-Cool air drops, so locate vents high enough to blow air on/past people.

Always fill by volume with good scale! Approx 1.8 lbs for a standard Vintage

            System.                

TIPS

Make sure cooling system and radiator are able to handle the extra heat.

Remember, without adequate airflow, a radiator is just a reservoir for hot water. 

            In general,   coolant transfers heat to radiator tubes, tubes transfer heat to fins, and

movement of air through   the fins removes heat from the radiator.  You must allow air

to pass efficiently through the radiator and out!

Allow for air to escape from under hood.

On radiator try to use a 15-18 lb. cap. Each pound pressure raises boiling point 
        
            3° F.  

Always use a thermostat to control engine coolant temperature.

 Remember:  Anti-freeze also increases boiling point. Use proper  mix (50% / 50%).

 Corrosion inhibitors protect against rust & mineral build-up  that reduce heat

             transfer. If using an engine driven fan use a shroud.  An unshrouded fan only moves

            air through the portion of the radiator equal to the circle of the fan.  A shroud

           dramatically improves the  efficiency of the fan and airflow does benefit from the

           housing effect the shroud provides.  An unshrouded fan moves about 50% the

           volume of a shrouded fan. 

Water pumps can be overdriven 30 – 35%.  (Pulley ratio - crankshaft pulley should

be 30% larger than water pump pulley) This will increase both air and coolant flow.

Mechanical belt driven fan should be ½ to 2/3 inside shroud for best performance.

An electric auxiliary pusher fan mounted to the grill side of the radiator will always improve the performance of an A/C system and keep the engine cooler.  It should be controlled by a pressure switch that turns it on only as needed.  It does not need to be on when the vehicle is in motion over about 20 mph.  We recommend installing a Trinary switch to protect the compressor from too high or low pressure and for engaging the electric fan as needed.  The auxiliary electric fan should be added whenever possible.  Or the primary electric fan should also be controlled by the Trinary switch as well as by engine coolant temperature.

A/C Terms:

Evacuate- Pull a vacuum on the system.  This removes air from the system.  Air has    moisture and takes up space.   Putting refrigerant in to a system without pulling out the   air first will cause a high pressures and poor (if any) cooling. 

Recharge-  Injecting refrigerant into a previously evacuated A/C system. Freon can be put into the high-pressure side as a liquid prior to starting the engine and engaging compressor. After engine is running it must be put in thru the low-pressure side slowly.  Always measure how much you have put in. 

Recover- Taking the refrigerant out of the system and putting it into a can for filtering and using over again.  It should not be discharged in to the atmosphere.