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How A/C works in your vintage car


#1

It’s time to dive into some nice, cold air. Last week, I explained why a guy from Massachusetts became so obsessed with having working A/C in his vintage cars and also described why the A/C needs of a vintage car are different from those of a car built after the switch from R12 to R134a refrigerant. This week, I’ll give you the theoretical underpinnings for how A/C works in the automotive environment.


This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2018/04/30/how-ac-works-in-your-vintage-car

#2

Great explanation Rob. You have a gift for simplifying complex topics. My only add would be that many vintage ac system problems arise from improper evacuation after a system has been opened. In short, all of the atmospheric moisture has not been removed before charging the system. When that moisture passes through the expansion valve, it becomes ice which closes or restricts the expansion valve, shutting down the cooling effect of the refrigerant evaporating (latent heat absorption). You have mentioned this issue in your previous Rondel writing when you covered proper vacuum pump evacuation and filter drier replacement. I really like the way you take on these potentially intimidating technical topics.


#3

Explanation of the pressure switch function is backwards. The switch closes on pressure rise, to reinitiate compressor pumping and cycles off at a low pressure condition.


#4

I used to do all the a/c work in the Firestone store I worked at 30 years ago and I am just now noticing that I never ran into an issue with expansion valves. Virtually all repairs were made on fixed orifice tube systems.
I remember being told by the instructor at the a/c course I took that the most important thing to always remember is the refrigerant state in the four areas of the a/c system. He drew a rudimentary diagram of a typical a/c system and drew an X through it dividing it into the four states. I still remember it, and always used that in diagnosing problems. Do enough systems and you can use your hands on various parts of the high and low side lines to give you a good idea of the state of the system by the temps you feel. Excellent article to help simplify the system.


#5

Really great explanation of a/c except that pressure in a container actually RAISES the boiling temp. Think of a automotive cooling system, if you have no radiator cap and just water, the coolant will boil at 212 degrees, but if you have a 10 pound radiator cap the boiling point will rise to 242 degrees(3 degrees for every pound of pressure)so what happens is when the refrigerant LOSES pressure by way of the restriction opening(txv valve,etc.) the boiling point of the liquid lowers causing boiling at that point


#6

Correction:::/:so what happens is when the refrigerant LOSES pressure by way of the restriction CLOSING(txv valve,etc.) the boiling point of the liquid lowers causing boiling at that point