Filling R134a from high side in liquid state with engine *OFF*

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WestPoint
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Filling R134a from high side in liquid state with engine *OFF*

Post by WestPoint »

Greetings fellas and fellettes,

I'm in the process of wrapping up my AC (and cooling system) overhaul on a 2004 Honda CRV.

I came across several posts on the web where experienced guys fill a can of R134a upside down as a liquid into the high side while the engine is OFF. They say it is ideal as it gets the compressor working with refrigerant now in the system and thus is much faster than doing gas/vapor fill from the get-go. Also, there is no chance of slugging the compressor when filling liquid in the high side (can upside down) as it's on the other side of the AC system.

Has anyone done it this way? It sounds like if you gas fill R134a from the low side (suction) it can take a long while for the car to pull in the 18.7 oz (max) of refrigerant.

Any thoughts would be greatly appreciated. Keep it one hunid.
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JohnHere
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by JohnHere »

WestPoint wrote: Wed May 19, 2021 8:36 pm Has anyone done it this way? It sounds like if you gas fill R134a from the low side (suction) it can take a long while for the car to pull in the 18.7 oz (max) of refrigerant.
Yes, you can do it. But why? A long while? Not true. Why not avoid the potential risks of charging liquid into the system, pull a vacuum in the normal manner, and charge into the vacuum through the low side with gaseous refrigerant using an accurate refrigeration scale? It'll only take a few minutes, and the compressor won't engage anyway until you have sufficient refrigerant in the system.
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Cusser
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by Cusser »

JohnHere wrote: Thu May 20, 2021 5:19 am pull a vacuum in the normal manner, and charge into the vacuum through the low side with gaseous refrigerant using an accurate refrigeration scale? It'll only take a few minutes, and the compressor won't engage anyway until you have sufficient refrigerant in the system.
I'm NOT an AC professional, but I do this JohnHere's way.
Al9
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by Al9 »

AC amateur point of view. It's a hard and delicate task, but ensuring the system is filled with the proper amount of refrigerant right before turning the compressor on is the only way to ensure correct oil return. Any other way, the compressor is unfortunately going to suffer some wear during the charging process. Will not necessarily mean compressor seizure, but cooling capacity may decrease somewhat. Especially with variable displacement compressors, where a larger than normal cylinder/piston clearance means more crankcase bypass and a harder time keeping the right displacement.
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WestPoint
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by WestPoint »

Assuming the compressor is already filled with PAG, how is there wear on the compressor if the clutch doesn't engage and AC is not on?
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WestPoint
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by WestPoint »

I'm still confused as it seems the vast majority charge through the low-side as a vapor. But enough still charge as a liquid through high-side as refrigerant is in a liquid state on high-side anyway, plus engine is off. It almost seems like it's taboo that's why I'm trying to get clarification if it's ok.

https://www.autoacforum.com/viewtopic.php?p=476#p476

My plan is to vacuum down to 300-400 microns and ensure it stays below 1000 microns after 30 min. While the system is under a vacuum, add liquid refrigerant (can upside down) on high-side and see how much it will take. Afterwards, vapor fill the rest with engine running.
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by Tim »

Simple answer.

If you hook up the gauge set and try to charge on the high side while the vehicle is running. You will blow your fingers off as you will be adding pressure into the can.

So if you want to get in the debate on charging. People go to extremes.

You can charge by a liquid on the low side. Just do it slowly as to not slug compressor with refrigerant. This is how it has been done for many many years.

You can charge on the high side if you have an R&R machine that works this way. It's done by the R&R machine while the vehicle is off.
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WestPoint
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by WestPoint »

Tim, thank you and I'm well aware that it's dangerous via the high side while the engine is on. I was merely asking why more people don't do it while engine is off.
Al9
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by Al9 »

WestPoint wrote: Tue May 25, 2021 11:25 am Assuming the compressor is already filled with PAG, how is there wear on the compressor if the clutch doesn't engage and AC is not on?
Indeed, the clutch gets engaged at some point, and that's when the poor compressor's bad day begins.
This is one example of what may happen when trying to fill as vapor through the low side. Delphi Harrison V7 compressor here.
https://www.autoacforum.com/viewtopic.p ... 712#p20712

Basically, eventually the operator engages the compressor so to draw enough refrigerant in/speed the charging process up, and that's when the compressor starts getting abused.

It doesn't matter whether the compressor is filled with lubricant or not. No oil sump and no dedicated oil pump means that some oil gets invariably discharged over time, and that the compressor needs to rely upon a good enough refrigerant flow (TXVs carefully designed to drop superheat near 0, or, in MVAC terms, flood the evaporator, as evaporator temp approaches 32F, is one example of how proper refrigerant flow is ensured with modern MVAC systems) to get this invariably discharged amount back. Otherwise it gets bone dry in no time, even if it was properly filled with oil.
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WestPoint
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Re: Filling R134a from high side in liquid state with engine *OFF*

Post by WestPoint »

Thanks for the info. So everyone compressor that gets filled as vapor via the low side suffers immediate wear and tear?

If that's the case, why aren't more filling through high side with engine OFF? All those Youtubers have been doing it wrong then!
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