Subcooling is way high -- Need Advice!

**beenthere** · 12-10-2012, 07:02 PM

Quote:

Originally Posted by hvac5646

I'll take this one for Uncle....
You sure about that?

After all, we are talking resi, not industrial or heavy commercial where a 20 cfm vac pump would be used.

Beenthere, you are agreeing with the gent from Howell..care to lay down some empirical data to prove your point.

Speak now or forever hold your peace.

There is no real thermal mass. Only the small are where the moisture is laying at.

You can put water in a baby food jar and freeze it by vacuuming it. or use the largest mason jar you can find. It will freeze when vacuumed quickly. Done it already. there are several videos on youtube.

paytonhvac has one of the vids on it. Along with another member from over there.

As NiNe 0 said, no thermal mass since there is no heat in a vacuum(no sound either).

On those systems that the vacuum keeps rising to 1000 microns. often its because the moisture did freeze and you are now seeing it thaw, or sublimation occurring.

hvac5646 · 12-10-2012, 07:17 PM

Quote:

Originally Posted by beenthere

There is no real thermal mass. Only the small are where the moisture is laying at.

You can put water in a baby food jar and freeze it by vacuuming it. or use the largest mason jar you can find. It will freeze when vacuumed quickly. Done it already. there are several videos on youtube.

paytonhvac has one of the vids on it. Along with another member from over there.

As NiNe 0 said, no thermal mass since there is no heat in a vacuum(no sound either).

On those systems that the vacuum keeps rising to 1000 microns. often its because the moisture did freeze and you are now seeing it thaw, or sublimation occurring.

Your forgetting the oil is in contact with the compressor housing and the tubing. The heat would conduct from these areas of mass to the moisture to stop a freeze from occurring.

And i wish to reiterate, this is a resi system ..not a system subject to possible flooding like a chiller or other indirect refer system.

Yeh vacuum is a good insulator...but even celestial bodies experience heat gain in outer space.

**beenthere** · 12-10-2012, 07:58 PM

Quote:

Originally Posted by hvac5646

Your forgetting the oil is in contact with the compressor housing and the tubing. The heat would conduct from these areas of mass to the moisture to stop a freeze from occurring.

And i wish to reiterate, this is a resi system ..not a system subject to possible flooding like a chiller or other indirect refer system.

Yeh vacuum is a good insulator...but even celestial bodies experience heat gain in outer space.

They gain heat by radiation(radiant heat), not through convection. Which is why the dark side of the moon is around -280°F. No atmosphere to conduct heat to it.

Do the vacuum test on a baby food jar. The water is in contact with the glass(a poor insulator) which is in contact with another surface area that is warm(counter/work table/what ever its set on). The water will still freeze.

Patrick Eubanks · 12-10-2012, 08:24 PM

Is this unit a nordyne product with a micro chanel coil?

Patrick Eubanks · 12-10-2012, 08:40 PM

Are you sure about that low side temperature reading?
Are you sure that there was no ice on the indoor coil?

hvac5646 · 12-10-2012, 10:00 PM

Quote:

Originally Posted by beenthere

They gain heat by radiation(radiant heat), not through convection. Which is why the dark side of the moon is around -280°F. No atmosphere to conduct heat to it.

Do the vacuum test on a baby food jar. The water is in contact with the glass(a poor insulator) which is in contact with another surface area that is warm(counter/work table/what ever its set on). The water will still freeze.

Take that same amount of water and put it in a large volume metal vessel (comp shell and evap and piping). There is a hell of a lot more mass for heat to be conducted to the cold and keep the temp up.

And since we are talking the inside of a comp shell the heat absorbed by the shell will conduct heat into the moisture. Vacuum or not.

BTW the moon has no moisture to hold the heat, air(atmosphere) is a lousy conductor of heat. That is why the desert areas get so cold at night. No water to act as a heat sink.

**beenthere** · 12-10-2012, 10:07 PM

You can put the water in a 55 gallon drum. It will still freeze. Only the mass where the water comes into contact counts.

Try a few experiments at your place.

The OP can do his own test, and he'll see how easy it is to freeze water in a vacuum.

hvac5646 · 12-10-2012, 10:48 PM

Quote:

Originally Posted by beenthere

You can put the water in a 55 gallon drum. It will still freeze. Only the mass where the water comes into contact counts.

Try a few experiments at your place.

The OP can do his own test, and he'll see how easy it is to freeze water in a vacuum.

Didn't say water can't freeze in a vacuum. I said the likelihood of it happening in normal service practice of resi applications is practically nil.

The "Wives Tale" is that using too high a capacity vac pump is going to freeze the moisture because it pulls down too quickly and you won't dehydrate the system. The other misconception is you'll vaporize the system oil.

Yeah, if I am trying for a ten micron vacuum for several on a resi a/c...

**beenthere** · 12-10-2012, 10:51 PM

Try the test I said about. You might be surprised how quick a small amount of moisture does freeze.

hvac5646 · 12-10-2012, 10:55 PM

Quote:

Originally Posted by beenthere

Try the test I said about. You might be surprised how quick a small amount of moisture does freeze.

Never said it wouldn't...in the test you purpose...but not in a resi system... U are comparing apples to oranges.

**beenthere** · 12-10-2012, 10:58 PM

It will and does. Many prefer not to believe it though.

hvac5646 · 12-10-2012, 11:04 PM

Quote:

Originally Posted by beenthere

It will and does. Many prefer not to believe it though.

it will and does what...O' Master Of Spin?

And whom are they that "...prefer not to believe it"...believe what?
That it does or does not happen?

**beenthere** · 12-10-2012, 11:07 PM

If you can't figure that out. Then no use for me to try to explain it.

hvac5646 · 12-10-2012, 11:23 PM

Quote:

Originally Posted by beenthere

If you can't figure that out. Then no use for me to try to explain it.

Your spinning the whole thing...do the math ...literally. How much capacity would the pump have to be pulling thru 1/4" schraders using 1/2" hoses?
And at how many PPM and how fast would the evacuation have to be to freeze water?

And even if it did freeze (which I submit it stands very little chance of) good service practice would dictate an oil change and sweeps with an inert gas. Would take a little longer yeah. But not much.

I have worked on unitary and split systems that sucked water thru a evap leak. After repairing the leak and blowing dry co2 thru the system there was still enough moisture in the system to cause me to change oil a few times... a six cfm pump....never had a freeze up.

**beenthere** · 12-10-2012, 11:30 PM

Or you just didn't take notice to the freeze up.

Past my bed time. Good night everyone.