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Np. Look up PSIA and PSIG. It's hard to understand anything in refrigeration without understanding that 14.7 psia = 0 psig = 1 atmosphere.

Excellent advice.
You see thats the kind of thing that I personally did not realize.
I want to study HVAC all I can and I sure do appreciate the help.

BTW, beat this into your head. Zero psig does not mean empty.

Why is this an important distinction?

If you braze on an "empty" system that's at 0psig and sealed you are going to get an explosion and a good dose of phosgene gas. It's an easy mistake to make.

Same thing if there is trapped liquid in the lines.

It also can be lot of refrigerant and you are required to recover to certain levels of vacuum based on system, etc.

Please be careful.

BTW, did I mention that it can go boom?

Originally Posted by BeaMage

I know know that it could'nt happen like like that as long as there is any remainig refrigerant in the system.

ThanX all.

Not true. Even at 0 PSIG, there's still 14.7 pounds of pressure from refrigerants in the system. Depending on the size of the system, that could be a lot of refrigerant.

You might correct that statement to "as long as there is any LIQUID refrigerant in the system." If there's liquid in the system, it can replace the vapor coming out, especially if you (as you should) heat the compressor, lightly tap with mallet to release trapped refrigerant, etc.

Also thanks for your reply Cowpoke.

I kept thinking if there was a leak on the low side (on type1 or type 2 systems), and the passive method is used, then the compressor would be pulling air in from the leak.
I know know that it could'nt happen like like that as long as there is any remainig (EDIT:liquid)refrigerant in the system.

ThanX all.

Thanks for the reply clearchris.
You made a light bulb come on for me.
I must have been overlooking the fact that if there is any refrigerant even on a system mostly empy, there would still be positive pressure due to the nature of the gas expanding.

Originally Posted by clearchris

If a system is leaking, generally refrigerant goes out because system pressures are higher than atmospheric pressure. There are some exceptions, such as chillers which run below 14.7psia (0 psig).

IIRC, regardless of the recovery system, for type 1 and 2 systems (not chillers), if there is a leak, you are not required to recover below 0 psig (atmospheric pressure) as this would indeed draw air and moisture into the system. If you are able to isolate the leaking section, you are required to do so, and recover the non-leaking part to required vacuum.

If there is air in a recovery vessel, if left still for a few days (not exactly sure of the time frame) it can be bled off the top as air is lighter than refrigerant and will settle to the top.

If I'm wrong on this, someone plz jump in.

That's what I always done. Bled the air from the tank. You can even check the tank for non-cond. Using the TP chart, and known refrigerant in tank, the pressure in tank, converted to temp, should be pretty close to exact room temp(if room temp stays fairly steady).

If a system is leaking, generally refrigerant goes out because system pressures are higher than atmospheric pressure. There are some exceptions, such as chillers which run below 14.7psia (0 psig).

IIRC, regardless of the recovery system, for type 1 and 2 systems (not chillers), if there is a leak, you are not required to recover below 0 psig (atmospheric pressure) as this would indeed draw air and moisture into the system. If you are able to isolate the leaking section, you are required to do so, and recover the non-leaking part to required vacuum.

If there is air in a recovery vessel, if left still for a few days (not exactly sure of the time frame) it can be bled off the top as air is lighter than refrigerant and will settle to the top.

If I'm wrong on this, someone plz jump in.

Air and the refrigerant recovery process.

On a a/c system that is leaking:
What happens to the air when using the passive method of recovery?

Is something different going on with the air when you are using the active method of recovery?

From what I understand "air" is considered a "non-condesable" item, and you would not want the air to show up in your recovery vessel.