Automotive Air Conditioning Information Forum

my system calls for 27oz of 134a.
when i zero out my scale should i allow a little more than 27oz to be weighed in to account for what will be left in the manifold hoses( i will close the high side coupler and freon tank and ball valve on the end of yellow line near freon tank and try my best to get as much of the freon out the gauges.
or should i weigh in exactly 27oz

If you are weighing in this R-134a with a tank on a scale, then you are measuring what leaves the tank and goes into the vehicle and the manifold/hoses. Once you have 27oz leaving the tank, then you shut off at either the tank valve or the charging hose valve (I use a 4 valve manifold so I have a valve there), I always shut off at the tank.

Next you can start the vehicle A/C system (or maybe you already had to), disconnect high side hose from the vehicle. Open all the valves with refrigerant still in them, and let this refrigerant get sucked into the low side port. What refrigerant remains in the manifold will be highly superheated low pressure vapor, probably like 0.5 grams of refrigerant mass.

TLDR Summary: Weigh in exactly 27oz and then suck all of it in the system.

do you have to disconnect the high side line or can you simply just close the coupling dial

can you simply just close the coupling dial

yes if you mean the thumb screw on the quick coupler

It is known as bleeding the hi side hose back into the low side

i guess i'll disconnect it as well and attach it to the manifold just to avoid a mistake