Here are some useful and helpful tips on refrigerant charging pertaining to your aircon.
- Refrigerant charging takes time, do not get in hurry or you will increase the chances of making a mistake.
- Do not put liquid refrigerant into the system, compressor damage may occur.
With your gauges hooked up and a third hose hooked to the refrigerant tank you open the tank slightly with the valves closed on your gauges and unscrew the tank hose close to the gauge manifold to release the air in the hose then tighten the hose securely. Do the same for the two hoses hooked to the system, open the valve on the tank and open the low side valve on your gauges allowing the vapor in the tank which is at a higher pressure than the low side of your system to flow into the refrigerant circuit. You need to be monitoring the temperature readings on your subcooling or superheat (preferably both) this will tell you the effect of the refrigerant that you are adding. If you are charging a TXV you should be looking for a high pressure reading corresponding to a temperature 20-30 degrees above your outdoor temperature (ex. 275psi r-22 =125 degrees this would be a good reading on a 95 degree day). If you are charging to superheat use the same method of adding refrigerant and as your suction or low pressure rises the difference in the refrigerant temperature and the actual temperature will decrease what you have to watch out for is that as you add refrigerant to the system the system performance improves and your indoor temperature drops changing your conditions and therefore changing the temperatures you are looking for if you don’t stop every few minutes and take new temperature readings so you know what superheat to look for you could be in danger of making a mistake, take your time, do it right and re-evaluate often.
The reason this such a critical function is that most of the mistakes made by contractors involve this process and if it is not done right best case your unit is not operating efficiently and worst case you could overcharge the system flooding liquid refrigerant out of the evaporator into the compressor and causing thousands of dollars in compressor damage.
Here are some other helpful guidelines. The goal for outside is to get a full liquid line while keeping the head pressure as low as possible. On a newer unit 190-225 PSI of head is normal, on some older units (25+ years) 300 PSI of head on a 90 degree day is not out of the question and may be normal. Anything higher wash the coil (you’re right the coil should have been washed before you started, just checking to see if you were paying attention) and consider the unit may be overcharged.
* Warning: There are situations where due to the conditions of your system you may have lower than normal suction pressure and/or higher than normal head pressure. Usually lower than normal suction pressure due to low airflow (either intentional or due to restrictions) and any attempts to raise the suction pressure by overcharging will cause damage by flooding the compressor. The trick is to determine if this pressure is normal for this system. For example some systems 50-55 PSI (30-35 degree evaporating temperature) is normal. The secret to being a good aircon servicing technician is to determine if this is a normal pressure and leave it alone.
Information courtesy from Mike Newberry from the Aircon Repair
For more useful tips, please refer here – Aircon Guide