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Question DetailsAsked on 6/28/2016

Which service port do I add new MO99 freon in, liquid or suction?

New compressor outside, Vacuumed all lines, no leaks. Videos all say add MO99 as a liquid, but do not show which service port to use, Liquid (high side) or suction (low side) They show throttling blue handle, as unit is running, to prevent slugging the compressor, but no instructions on the initial 5lbs refill.

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1 Answer


Sorry to say it, but if you have to ask you are not qualified to do it - because there is more to it than just putting in some refrigerant - you need the fill tables for the gas versus temperature, the rating information for the system to tell you how much pressure needs to be put in (high and low side operating pressures), whether your TXV valve needs replacement or adjustment (if adjustable) for the different gas properties (if does NOT behave identically to R-22), plus it is illegal to put in refrigerant if you do not have the appropriate federal license.

You also have not said if you checked compatibilitiy - there are at least 4 different classes of oils used in A/C refrigerants - if you put in a gas with an incompatible oil you can really gum the works up and cause serious damage to the system.

Videos are fine for general info, but I would say have a professional Heating and A/C contractor do it.

Answered 4 years ago by LCD

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