Both my cars have somewhat modified A/C systems. One is 100% non-stock except for the evaporator core; and the other has more minor changes. When mix-matching a/c parts you must keep in mind these points. All A/C systems must have: compressor, condenser, evaporator, expansion device, a filter/drier, and a way to regulate the low-side pressure. Here are the basic A/C schematics for most mobile systems.

Usually, the parts that remain on the car and engine going in the car will determine what sort of system will be easiest to set-up. The early systems were very eomplex and leaky due to the millions of fittings, etc. Due to political pressure modern car a/c systems are required to be as leak-free as possible; and I like to incorporate these designs into my hybrid systems.

My Nova had an A6 compressor. This huge hunk of iron went with the worn out 307 engine. I ripped out the rotten hoses, evaporator pressure regulator valve, expansion valve, rusted out receiver/ drier, and punctured condenser. I was left with an evaporator core original to the car. The engine had a radial-4 compressor on it, from the Camaro. I dug around in the shop where i worked and found a new condenser that was about the right shape, and plenty big. It was ordered for a customer and was the wrong part for her Mercedes but I easily adapted it to mount in front of my Nova's radiator. At this point I could have either used a receiver/ drier in the high-pressure line along with a thermostatic expansion valve; or an oriface tube system with an accumulator tank in the compressor suction line. I was delighted to find out the same threads are used on the old EPR valve as on a standard accumulator/ drier. I found out talking to mu favorite auto parts place that an oriface tube adapter would fit in place of the original expansion valve so that completed my system. A set of hoses were made up to my specifications; including fittings for my specific compressor and other components.

After flushing out all the used components, adding the correct oil and charging the system, it worked! The air was cold but the compressor (which came on this used engine) was in bad shape. It was noise and as it cycled on and off you could hear and even feel the drag on the engine. I junked that R4 compressor in favor of the Delco Variable-5 unit pictured below. These compressors can adjust their stroke volume to keep the pressure on the low-side near 30 psi. This is where it needs to stay for best performance without freeze-up. Regardless of heat load on the a/c, and regardless of engine speed, this compressor will run all the time, decreasing and increasing its capacity as the conditions change. Doing so it matches its power usage with the amount of work it needs to be doing. There is no a/c "surge" while driving.

While looking through the junkyard for a suitable V5 (there are many different mounting base configurations) I noticed a few had a smaller pulley which will further increase pumping capacity at low engine speeds. The smaller the pulley the better. Charged with R134A this system as shown will cool to 39ºF on a blistering hot day, engine at idle. What you see in the picture is all there is, aside from the condenser. Virtually no underhood clutter and only 3 hoses to leak.

On 70's Novas, there is a bad design in the in-dash air system. When in "Max" mode, the under-dash air intake for the blower is restricted badly by a cover, and a door that doesn't open all the way. Also, make SURE the outside air door (under the cowl at the bottom of the windshield) is closing in A/C mode. If not, you are pulling in superheated air from under the hood. I took the door out of the interior air intake, and drilled the cover as shown to eliminate any restriction to the air entering the fan. Fixing these 2 things made a DRAMATIC difference in airflow (doubled!) and in coldness. This car is older than I am and has always been in the family. At no point do I remember this forceful of airflow. Now it blows as well as new cars these days.

Liquid line temperature sensor on 86 Buick Century used for cooling fan speed control. No room for pressure switch due to turbocharger exhaust downpipe. This thermistor tells the fan control module when the liquid line (and thus the condenser) are getting hot and turns on or speeds up the fan as needed. Same module that uses this sensor could shutdown the compressor if it overheats, or slow down the interior blower fan. This would lower the load on the compressor.