Yup, the low side. Question is, is the system low or out of refrigerant? And where is the leak? If the system has run in a vacuum and the leak is on the low side it will have air and moisture in it. If it is R134a it would be best to change the oil and pull an evacuation (after fixing the leak) before charging. Excessive head pressure can result from air and moisture being in the system. This will also cause a restricted metering device and compressor damage.

So by just adding gas you are only biding your time till something major goes wrong.

I am EPA universal certified HVACR tech 801 and 802, but seems Joe public can buy R134a over the counter without a license.

One more thing is if the system is R12 you will have to convert to R134a which means changing the oil type and the hoses.

Note that R134a has a smaller molecule size and will leak faster through the same size hole. This is the reason for the hose change.


This would be a good time to have a leak check done before making repairs so you know what you are looking at.