Opening service valves

[jack david]

With full charge in condensor (service valves closed), which valve would you open first? I remember the part about opening the valve slowly to keep the oil in the compressor, but for some reason I can't remember which one to open first.

[airmechanix]

...liquid line first

[dmoneyc22]

after a leak test or pressure test of the system and an evac of lines and coil are completed you must open the liquid line valve 1st

[amickracing]

I've heard and practice this also... but I've never really heard of an answer. My belief is because this is the way the refrigerant would normally flow (and wouldn't try to flow backwards throught the compressor).

So whats the professional answer y'all?

[pop]

Pull Vac. Add any Additional refrigerant by weight required because of line set length and dryer Volumn, Add through Liquid line, release slowly liquid line first, when equalized open vapor side. and above all have fun.

[jack david]

Thanks for the replies. The light bulb just went on. I was taught to first crack the liquid line (slowly). The reason I was told was because if the vapor line was opened first that the escaping gas could draw the compressor oil with it. Don't know if it's true, but that's what I was taught in school.

[duct dr]

Exactly right pop, but remember to use a VAC guage and pull to at least 400 microns. Then pressure test to ensure no leaks.

[jrc2905]

Don't you mean pres. test first then vac?

[fat eddy]

Liquid line first, because if you open the suction line first you will pull liquid back through the compressor (scroll)and have liquid laying in the compressor on startup. On recips remember those valves are not 100% when the unit is not running if you have liquid laying in the piston head it will migrate to the low side. Another reason is that you could suck oil out of the compressor by opening the low side first.There are just a a whole slew of reasons for doing it that way, and no good reasons for doing it the other way.