Guys, my Accumulator? (the silver canister) on my little pickup is icing over. What would cause this?
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NMCB 28 Seabee Battalion

Low refrigerant.

Gauges show it has plenty of refrigerant.



Let me ask a general AC question: why is it important to run a vacuum on the system if you ever open the lines for any reason? Would it damage the system if the orfice tube were replaced, system recharged, but no vacuum pulled?
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NMCB 28 Seabee Battalion

You pull down a vacuum on the system to evaporate and evacuate any moisture in the system. Once you open a system, just normal atmosperic moisture is enough to cause a malfunction since it take only a drop of water to freeze in the orifice. The longer the system is open, the more acute the problem is. The receiver/dryer is supposed to capture and hold any water in the system but its capacity is quite limited and will trap only a small amount of incidental moisture. This is why it is SOP to replace the dryer whenever you have the system open for an extended duration. I can't say precisely how long "long" is but if I had a system that was open for a day or one that had been empty for a long time, I'd reoplace the dryer. At least this is how shops normally do it unless they want to see comebacks.

I have an A/C vacuum pump and gauges. I'm not an expert but I have picked up a few of their best practices. One thing you should do when you are charging a system is to bleed down the gauge lines to purge air out before you open the manifold valves. Once the high and low side lines are purged, you connect your refrigerant can and crack open that hose at the manifold to purge air out. Now all the lines have refrigerant in them and you can run and charge the system. This helps to ensure you are not putting moisture into the system -particularly one you have already pumped down.

The reality is that many times, systems are opened, worked on, filled up without following all the precautions and everything works. So it appears all of that other stuff is just excess. But on occasion, something will not go right -like a moisture issue- and there you have it.

That the accumulator is icing over means you have refigerant evaporating in the accumulator, which is supposed to store liquid refrigerant from the condensor. So you either have insufficient refrigerant in the system or the accumulator inlet is blocked either by debris in the inlet filter (very common problem) or frozen moisture.