Replaced my AC condenser

While it is evacuated? Is that even possible? Searching...

Yes, it is possible with a special tool which has a built in valve and very long rod for pulling out the valve core. Pretty cool actually. Shown in use here

starting at 45 seconds in.

Before finding that video I had only ever seen the simple Schrader valve tools, used on bicycles, for instance. Variants of this:

https://www.onallcylinders.com/wp-content/uploads/2023/06/02/Schrader-valve-on-table-with-tool-and-tube-2-scaled.jpg

Wait, that tool is for replacing the valve core while the system is pressurized. The pressure helps keep the core stuck in the rod while it is moved in and out past the valve in the tool. If the system is evacuated that pressure would be absent. Guess it might still work but maybe the core would be prone to falling out.

 

The simple tools can be used if the system is evacuated, The fancy tool in the video allows the replacement of the valves without having to vacuum the system down. So it is horses for courses.

 

What exactly does "evacuated" mean in car AC systems?

It has been many decades since I last worked on one, but in other vacuum systems "evacuated" meant that the system was currently holding a vacuum. Not just no refrigerant inside, but no, well, extremely little, gas of any type. The state of "physically open to the atmosphere" was called "open". So using the simple screw driver like tools to swap a valve on the "evacuated" system would convert the system from "evacuated" to "open" when the core came out. If the core was changed really fast it might not let in enough air to get all the way back up to 760 torr, but in electron microscopes and the like even a couple of torr is way too much gas.

 

As I understand it, evacuating is removing the refrigerant. Drawing a vacuum or vacuuming down is removing air and moisture after the system has been open for say a compressor or condenser replacement.

So to replace the valves in the service ports you evacuate the refrigerant then release the vacuum effectively opening the system and change them. Then vacuum it down and recharge. You'd only really do it this way if you were doing other work anyway, or you needed to evacuate the system to measure the weight of the existing refrigerant.

 

Great tip! Will do that next.

 

One could maybe evacuate and then let in enough nice dry inert gas to match atmospheric pressure, and then you could change the cores in a leisurely fashion and pretty much nothing would happen, and you get the inert gas back out when you vacuum it again.

If you just evacuate it and then open it removing valve cores, it'll suck in a whole system's worth of nasty wet atmospheric air. Which you'll also be shortly vacuuming back out again, but still ....

 

I'm now wondering whether the machine reinserts R134a to equalize to atmospheric pressure so the system can be opened. There is certainly no inrush of atmospheric air when the valves are removed. That sure would be fun trying to get the valves out with 30 inHg of vacuum on them.

 

30 inches Hg vacuum is just under 15psi pressure. Times the tiny cross section area of a valve core equals a very small total force.

All of which doesn't matter. As you loosen the valve core, its base no longer seals to the port so pressure equalizes by the time you remove it.

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I didn't try that yet... Just been running through a can of coolant every couple to three days...

Definitely will try that next. I didn't realize (or think about the logic) that the valves can't show up as failing while connected to the vacuum test...