for car or for home?

Malaysia without 4 season western country different their ac can reverse as heater there are pro and con

In Malaysia most ac mam drop by without vacuum after disassemble ac unit below 2hp unless owner requested

Malaysia labor cheap AC also cheap after 8 year usage too much noise too much problem replacement cheaper than repair

Of course you can learn all this proper way diy and maintain your own house ac, but you can buy ac servicing kit without removing whole indoor unit all those servicing unit sold at online with small water pressure pump already sufficient

Run it and check pressure, use gauge. And topup, dont overfill. Dont forget change the cheap valve.

After initial full filled, you can rely on pressure, but if there is leak, just use low side pressure as indication.

Typically you need to weight the gas bottle, else mere experiment / experience on right volume by weight. For car got eyesight, should have similar for house. You diy service / refill?

The subcooling method is generally not used to check gas charge for domestic air conds in Malaysia as a TXV valve is not used in them. For orifice and piston metering devices, the super heat method is used.
There are many threads about which air cond is the best and most reliable, but I think that it actually comes down to the quality of the installer that determines it. No manufacturer is knowingly going to sell thousands of sub-par lemon air cond units and have to deal with the fallout of the units failing. But installers? Install, take the money and disappear, no cares given.

Greg, from AC Service Tech on the YT channel you linked is a good resource. A good install follows all the steps he describes and takes. This means having proper knowledge, and all the tools that is required. I warn you that having a complete set of tools is not cheap, and you may want to consider if you can rent them for occasional use, if installing/servicing is not your money making business.

Full disclosure : I am learning how to install and service air conditioning units, done properly, to supplement my income from my electronic/electrical/maintenance business. So far, after months of learning, I still have not installed a single air cond for a customer yet, as I can't confidently say I'm doing it correctly! I have repaired/serviced for friends and family at no charge to get experience though

ah yes sight glass

one more is u can fee the low pressure line chilled

need to find sweetspot

overall cheap to DIY especially if got many units at home

Car systems are vacuumed as the machine they use does it automatically. You don't have to hook up a separate pump, run it, and then watch the gauges.
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Here is the short form of checking if there is enough refrigerant in your air cond:
1. Find the Target Superheat for the room
Measure indoor Wet Bulb temperature, and outdoor Dry Bulb temperature, then refer to Superheat chart.
2. Find the [b]Total Superheat for the air cond unit[/B]
Measure the gas line temperature - the saturation temperature of the core
3. Determine to add, remove, or maintain refrigerant gas based on Total Superheat being larger, smaller, or equal to the Target Superheat.

How do you think the tech will purge the lineset ?

What good is then new units come with factory prefilled gas ? May as well sell 'kosong'