What you need to know when buying an automotive Compressor

There is a misconception about automotive A/C Compressors.  Many times we have had people ask if a bigger Compressor will help the car cool better.  Other times people will blame the poor cooling on the Compressor.  A Compressor is made up of two main parts, the Compressor body, and the clutch assembly.  When we refer to a Compressor we are referring to the complete Compressor and clutch assembly. 

The function of a Compressor is to pump the refrigerant, R-12 or R-134a, and the oil through the system.  If a Compressor is thought of as a pump it might be easier to understand how it cannot have any major control over the temperature blowing out of the vents.  There are many different types of Compressors, the most common are Rotary Piston Compressors, Scroll Compressors and Variable Displacement Compressors.  In the 1950's through the 1980's A/C Compressors had a pump style A/C Compressor.  These Compressors required oil to always be in the Compressor housing similar to an automotive engine.  With these older types of Compressors (York, A-5, A-6, RV-2, and Tecumseh) the system would need some oil added to the other components in the system.  For instance, two ounces of oil be added to the drier, two ounces to the condenser and two ounces to the evaporator.  Today the times have changed, these old Compressors still work great but there is new technology that allows a Compressor to circulate the oil through the system, and use less horsepower from the engine to do it. Nostalgic AC only uses a piston style (Sanden) Compressor with all of their A/C kits.  These Compressors come pre-oiled with the proper amount of oil for our aftermarket ac systems.  The way these Compressors operate is by keeping three to four ounces of oil in the housing all the time while circulating the oil with the refrigerant through the system.  If you add to much oil to a system the oil will overwhelm the refrigerant and not allow it to covert from a vapor to a liquid, and a liquid to a vapor.  In turn this will cause the refrigerant to never get to the correct state and cool the car as it is designed to do.  For example, if you have seven ounces of oil in a system, and 24 ounces of R-134a the oil will not saturate the refrigerant which will allow the R-134a to transfer properties.  If you have a system with 10 ounces of oil, and 24 ounces of R-134a the R-134a will be too saturated to ever get to the perfect liquid state to allow the car to cool.  This is why we ask every customer to not add any oil to any part of the system.  We have done all the work for you, just assemble our system, charge it, and enjoy. 

The clutch assembly on a Compressor is made up of four parts.  The front outer most part is called the hub, the middle of the clutch is a pulley which has a bearing in the center of it, and the inner part (closest to the Compressor) is the coil.  Aftermarket Compressors will normally come with a two groove v-belt pulley, only one pulley is required to run the Compressor.  Single groove pulleys are not available for aftermarket applications.  If you have a serpentine setup the pulley may have extra belt "ribs" grooves.  The serpentine pulleys are only available with so many grooves, if you have a six groove belt, and receive an eight groove Compressor pulley the belt should be setup to sit in the center of the pulley.

A clutch assembly has one job to engage and disengage the Compressor.  The way this works is with the hub, pulley, and coil working as one when the A/C Compressor is on, and the pulley acting as an idler when the A/C is off.  If the A/C is off the engine will not have any strain on it from the Compressor.  The Compressor pulley will spin free when the clutch is not engaged.  When the clutch is engaged it is making the Compressor pump which requires horsepower from the engine, a standard Compressor will require about two to five horsepower.  The way a clutch assembly works is very simple.  The hub is attached to the shaft that is inside the Compressor, this shaft spins making the pistons pump the fluids through the valves.  The pulley is spun by the belt; the coil is similar to a magnet.  When the A/C is turned on the coil will act like a magnet pulling the hub against the pulley.  The belt turning the pulley turns the hub also because the coil pulled the hub against the pulley.  If a clutch is diagnosed as bad it is normally a misdiagnosed problem.  If a clutch gets too hot from a Compressor problem then it will cause the rubber on the hub, the bearing, and the coil to come undone.  This is what is normally diagnosed as a bad clutch, but by replacing the clutch you are only putting a temporary fix on a present problem.

Nostalgic AC sells many different Sanden rear heads.  The rear head or back of the Compressor can be changed if they break or a Compressor has a head on it that will not match the hose fittings.  We offer the most popular heads, but there are many more available, Sanden has more than 50 different variations of rear heads.  If you need to change the rear head the simplest way to determine the head, you have is to look for the letters in the center of the head. Not all Compressors will have the letter code on the back, most will.  The letters S and D, or SUC and DIS are the letter codes used to determine the type of head. If your Compressor does not have the letter code, you can count the number of bolts holding the head to the Compressor body.  A Sanden 508, 5H11. or any other five series Compressor will have five bolts holding the rear head on. A Sanden 709 Seven series Compressor will have six bolts holding the head on.

If a customer has an engine with a Compressor already mounted, it is not a problem to use that pump with the new A/C system.  We offer many different types of adapter fittings for the new style Compressors, if we do not have one listed for a specific application please contact us we can make any connection to any Compressor. 

On our website we list out the different cubic inch displacements for the different Compressors.  We do this to allow the customers to choose the Compressor that best fits their needs.  The smaller the Compressor the smaller the system, and the larger the system the larger the Compressor.  The 508 Compressor we have listed on the website is our most suitable Compressor, it can handle just about any system with front air, or front and rear air.  If room is a factor the smaller Compressors will work as well without causing any noticeable difference.