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.

Many, many years ago, I did see an installer use a vacuum pump to pull vacuum for an air conditioner, but since then, apa pun tada. 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

All systems must be evacuated, no matter what kind of gas is used. The air cond guys don't bother to evacuate the system because they are just not bothered to do so. Water vapor/other gases in the system changes the characteristics of the refrigerant gas, and the air cond doesn't work optimally. Water vapor will also cause the copper to corrode from the inside, since there still is O₂ (vacuum not pulled, remember?) in the system.

But what do they care? Finish the job, cold air flowing, take the payment and leave. Anything further is not their problem. I always lament that the quality of jobs done is crap, but then as someone in the industry, I can also say that part of the problem lies with the customer. Just try to charge an extra RM 10 to do a quality job, but the customer will hire someone else. So, unfortunately, the level of maturity has not been achieved yet by the installers as well as the customers.

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 Total Superheat for the air cond unit
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.