Quote:
Originally Posted by Shern
“Partial vacuum” is a point I can’t quite grasp.
So say I’ve pulled vacuum, I’m to let the drop-down a few HG before filling? Unclear…
And a point of practicality, what is the fitting style people typically use to connect those cans to the pressure ports?
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I’ve never understood it that well either. Apparently blends are either 60/40 or 70/30 propane/isobutane. The original 60/40 blend could be transported in thin wall containers, the 70/30 blend couldn’t.
The issue is that the isobutane keeps overall pressures lower, and more means that there isn’t as much working fluid. Remember that AC works on pressure changes, and more specifically, phase changes going from liquid to gas.
As I understand it, the higher amount of isobutane keeps pressures lower, but that affects the ability to compress and condense the propane working fluid. So you already had less. The result in automotive AC is that the compressor short cycles. To remedy this they want the original 12a to be charged into ambient atmosphere (system containing some amount of air). Of course air doesn’t condense and so isn’t a working fluid at all. So cooling is compromised. Charge to a vacuum and in order to get pressures high enough to operate and not short cycle the compressor then things are way out of whack on the high side.
The industrial 12a is packaged in thick wall containers that can be shipped and work better. It can be charged to a hard vacuum. I believe the industrial blend is the actual correct blend that is used in commercial (stationary) refrigeration systems.
The other issue is that this is a blend. MVAC systems are intrinsically leaky. So it will distill to a different ratio as the diffeeent components leak at different rates. So this means you need to somehow check or re-fill every so often if your system has a leak.
It also should be charged as a liquid in the high side. The issue is that it will draw oil away and the MVAC systems are intended to carry oil through the system. So you don’t want these blends which will carry oil to wash the internal surfaces clean.