How much AC compressor capacity do you really need?
That’s one of the questions hotrodders ask when adding or upgrading an AC system.
The leading manufacturer of AC compressors is the Sanden Corporation and here are some of the variations they offer:
SD5H14, formerly called the 508
SD7H15, formerly called the 709
SD7B10, sometimes called the 7176
Here’s what those model numbers mean: For example, the 508 meant the compressor had 5 cylinders and approximately 8 cubic inches of pumping capacity per revolution. The newer designation can be decoded with the 5 still meaning 5 cylinders and the 14 representing a metric equivalent of 140 cubic centimeters. And now you can figure out that 709 stands for 7 cylinders and 9 cubic inches and the SD7B10 has 7 cylinders and 100 cc capacity.
We still like to use the old model numbers because they are shorter and it helps avoid confusion of having two models begin with “SD7.”
So, the 508 and 709 share an external design, a long cylindrical body with 4 equally-spaced mounting ears at the front and 4 ears near the rear. Most often, there will be two threaded male hose fittings pointing up out of the rear cover plate. There is also an option which points the fittings straight out the rear.
The SD7B10 (we call it the “mini” compressor) is completely different. It is shorter and slightly smaller in diameter. It has two mounting ears at the top and two on the bottom. It does not have built-in threaded fittings but has two o-ring ports in the center of the top of the body. This means you have to add some kind of threaded fittings, the most common being 2 straight male fittings or a manifold with 90-degree hardlines with fittings on the ends.
Now, before we answer the capacity question, let us share some personal experiences with AC compressors.
We introduced our compressor bracket for Chevy LS engines in 2008 and not too long after that we also started selling compressors. At the time, the most popular compressor was the Sanden 508 and that’s what we designed our bracket around.
After selling several hundred compressors we got a call from a customer who said he had a strange harmonic vibration coming from his compressor, usually somewhere between 2000 and 2500 rpm. We sent a replacement and he said he still had the same issue.
So we called our compressor supplier and asked if they had experienced this vibration issue. They said, “yes”, we hear that occasionally and we don’t know the cause but the simple fix is to use the 709.
As we dug deeper into what the cause might be, we found speculation that Chevy LS engines were more prone to this vibration than other engines. Eventually, we had more reliable sources who confirmed that the 508 compressors were prone to harmonics no matter what the engine they were mounted on.
We took the easy way out and simply started selling the Sanden 709. It only cost $10 more than the 508 and had some bonus pumping capacity.
Now, you may know that we are a supplier to several AC manufacturers who include our brackets with their systems. One of those, Vintage Air, came to us with a problem. Their latest system, called the Gen V, is so efficient that the extra pumping capacity of the Sanden 709 causes the compressor to cycle off and on more often than ideal.
Vintage Air asked us to re-examine the 508 vibration issue to make sure that the source of the problem was not our bracket because the 508 capacity was better matched with their Gen V design.
We built several prototypes with different material thicknesses, different shapes and even a version made of steel rather aluminum since steel is stiffer. We tested different 508 compressors, we tested different levels of refrigerant and the results were the same—we still had vibrations. But, as soon as we swapped to a 709, the problem went away.
Our attention then turned to the SD7B10 mini compressor. We had developed a bracket for this compressor we call the “high & tight” but it only works with LS engines with either truck or 2010-15 Camaro balancers and water pumps. The short length of the mini compressor lets it sit directly in front of the cylinder head making it very compact and a perfect fit for cars and trucks with narrow engine bays like 1947-54 Chevy trucks. And we’ve never had a vibration complaint or a question about cooling capacity.
OK, time for another real-world experiment. A few years ago we had a 1950 Chevy street rod truck with an old-school SBC engine. We had cobbled together an AC system with a junk yard evaporator, a small condenser of unknown origin, a swap-meet electric fan and a Sanden 508 compressor. And it made decent cold air.
We then developed an SBC compressor bracket that used the mini compressor. We installed the new mini compressor but kept the rest of the sketchy AC system. And we had less cold air, especially at idle.
The truck was on an S10 chassis and was something we drove on a regular basis so we decided it was time to upgrade the AC system. We kept the mini compressor but installed a new Vintage Air Gen 2 evaporator, a high efficiency Vintage Air condenser and a kick-ass Spal fan. Now we could hang beef in the cabin!
Moral of the story? An AC system needs all the components to be compatible with each other and to be matched to the cooling load. A high-capacity compressor doesn’t help if the rest of the system is throttling it down.
You are probably asking yourself by now, “Are these guys ever going to answer the question about whether I need the mini compressor or larger HD version?”
And you know the answer is going to be, “It depends.” We believe that for most coupes, sedans and standard or extended cab pickups the Sanden mini compressor will work great as long as the rest of the system is rightsized. Exceptions would be station wagons, Suburbans and maybe cars with huge glass area like the bubble top Impalas.
That’s why we consider our new “wide-mount mini” bracket for LS engines to be our standard recommendation for LS swaps. We have part numbers to line up with any LS belt path—Corvette, F-body and truck/2010+ Camaro.
And if you have a vehicle that needs the extra capacity, we still offer brackets for the larger compressor.
For more info about the wide-mount brackets, see:
https://www.kwikperf.com/collections/wide-mount-brackets
For more info about “high & tight” brackets, see:
https://www.kwikperf.com/collections/narrow-street-rod-brackets