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#42 ·
A 75 OD temp should have given at least a 95* SCT. So is this system all good to go by fiddling w/ the thermal bulb?
A loose t'bulb should have given a low SH # or at least a fluctulating SH.
 
#46 ·
I had a journeyman come out. He found out that when another guy insulated the TXV, it wasn't done that well. We had to adjust the TXV as well. Now we have a superheat of 8 and subcooling of 6.
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dblaron717 said:
Idk. We took refrigerant out, adjusted the TXV, and insulated the bulb. Doing that we got it in range.
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Just for some clarity...the metering rate of the valve varies directly with the bulb pressure, which varies directly with bulb temperature.

The bulb likely needs insulation for accurate superheat values, but that wasn't causing the high superheat...an uninsulated or loosely attached bulb can sense more of the surrounding, higher air temperature and open the valve, causing lower measured superheat.

Most likely, the valve adjustment fixed the superheat, and the charge adjustment fixed the subcooling. ;)
 
Discussion starter · #47 ·
Thank you for the explanation. I am currently reading the AC/HP book and am learning more and more. Appreciate all of you that commented.


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#48 ·
As you have been an apprentice for a year now you are either in school or have completed it. In your school they would have told you the symptoms of non-condensibles in the refrigeration system.

What are those symptoms?

Which of them does your system have?

PHM
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dblaron717 said:
Stop step back and control your mouth before you respond. I have been an apprentice for a year now. I said i think it has non condensibles in it, but i am trying to gather info from smart people (obviously not you) before i overreact and pull out all the refrigerant.


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#49 ·
dblaron717 said:
Thank you for the explanation. I am currently reading the AC/HP book and am learning more and more. Appreciate all of you that commented.
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If there's a "secret" to acquiring skill with diagnostics, it lies in learning "how stuff works"...what's the machine supposed to do, and what has to happen in order for it to do it.

It's a simple concept, but difficult to fully master. I been at it 30 years and am still struggling...:grin2:
 
Discussion starter · #50 ·
Poodle Head Mikey said:
As you have been an apprentice for a year now you are either in school or have completed it. In your school they would have told you the symptoms of non-condensibles in the refrigeration system.

What are those symptoms?

Which of them does your system have?

PHM
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We have a state approved in-house school. You get about 3 months of classroom training and then after that you go out and basically wash units and take readings. When you have problems, you call in and they come out to you and briefly explain what is going on. Then in our full day once every other week we talk about what we have found and the reason behind it.

My needle on the high side was going up and down by roughly 15-20psi. I thought when this happened it was a sign of noncondensible. Someone yesterday said something about hunting and I assumed it was a misspelled word. A tech that came out explained it as the TXV trying to find the superheat balance. Since it was overcharged, it was reacting more he said. He also said if it was noncondensibles the needle would be rapidly going back and forth, not very slow like mine was doing.

If anyone can better explain this to me...I would appreciate it.


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#51 ·
I don't know of a sure fire, simple way to diagnose non-con's from the measured saturated temps and superheat/subcooling...assuming you don't know what the numbers were before the non-con's got into the system.
 
Discussion starter · #52 ·
Well thats the thing. After we took 24oz of refrigerant out, it wasnt "slow bouncing" anymore. So there wasnt any noncon in the system (from what I understood). How does knowing saturated and SH/SC relate to noncon? I thought it was the bouncing of your needles.


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#53 ·
dblaron717 said:
How does knowing saturated and SH/SC relate to noncon?
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Based on a very few confirmed systems with NC's...

The head pressure and subcooling will always be higher. Just how much higher would depend on the amount of NC'c. The suction might be a little lower and the superheat will be a little higher.

But those same symptoms could be due to a mild liquid restriction and overcharge. Or maybe a restricted outdoor coil and undercharge.

So, if you were familiar with a system's normal numbers, then discovered someone else had worked on it for some reason, then observed the symptoms, you might suspect there were some NC's involved.

If there's a sight glass in the system (and there usually isn't on resi), you might see bubbles.

Last time I suspected NC's (after wasting a lot of time and energy guessing at other things) I pumped most of the charge into a recovery drum and compared the actual pressure with the P-T value and it was higher...which pretty much confirms NC's.

Like I said, not an easy way to diagnose NC's, that I'm aware of.
 
#54 ·
I've only seen non condensables once. There was a leak in the suction line and the contactor was welded shut, so I know for a fact it sucked air. The repair wasn't approved for a few weeks, they just wanted it topped off temporarily. It ran fine when it was cool out, then it warmed up and wouldn't make temp. I left a hose spraying on it and it worked fine. I don't remember subcooling, just that head pressure was high.
 
#55 ·
If there are non condensebles in your system hook your gauges up and if your gauge needles or digital gauges are bouncing all over and fluctuating extremely its a given. I had 1 system where a previous company did a leak check and repair and when i hooked up....my gauges where going crazy. Reclaimed the charge tested for leaks and pulled a vacuum. No issues since.
 
#57 ·
I have found non-condensables in systems but I never seen the wildly fluctuating gauge needles that you describe.

Can you explain what it is about a system with 'air' in it which results in the wildly fluctuating manifold gauges?

PHM
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slickgoat05 said:
If there are non condensebles in your system hook your gauges up and if your gauge needles or digital gauges are bouncing all over and fluctuating extremely its a given. I had 1 system where a previous company did a leak check and repair and when i hooked up....my gauges where going crazy. Reclaimed the charge tested for leaks and pulled a vacuum. No issues since.
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Discussion starter · #58 ·
At the point of the refrigeration process, the compressor sucks in vapor compresses it and releases it as vapor. When liquid comes through it cannot be compressed. So I assume when the NCon come to the compressor that is when the psi on your gauge goes slightly up. The reason why i said up was because there is less volume in the containment area, therefore compressing the vapor to a higher psi. If I am wrong please let me know. When the liquid leaves it goes back. Repeat!


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#59 ·
My thought would be that the (I'm tired of typing 'non-condensables - let's use "air" instead)

The air vapor is just as compress-able as the refrigerant vapor. The air is not condense-able but it is certainly compress-able. The internal compression areas of the compressor would always be the same so why would compressing air be any different than compressing refrigerant?

You write: "when liquid comes through" - what does that mean? Are we talking about air contamination of the system or refrigerant liquid slugging? Neither one causes the other.

PHM
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dblaron717 said:
At the point of the refrigeration process, the compressor sucks in vapor compresses it and releases it as vapor. When liquid comes through it cannot be compressed. So I assume when the NCon come to the compressor that is when the psi on your gauge goes slightly up. The reason why i said up was because there is less volume in the containment area, therefore compressing the vapor to a higher psi. If I am wrong please let me know. When the liquid leaves it goes back. Repeat!


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Discussion starter · #60 ·
Poodle Head Mikey said:
My thought would be that the (I'm tired of typing 'non-condensables - let's use "air" instead)

The air vapor is just as compress-able as the refrigerant vapor. The air is not condense-able but it is certainly compress-able. The internal compression areas of the compressor would always be the same so why would compressing air be any different than compressing refrigerant?

You write: "when liquid comes through" - what does that mean? Are we talking about air contamination of the system or refrigerant liquid slugging? Neither one causes the other.

PHM
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I guess i was under the impression that NCon was when you didnt remove all the condensation from the lines during a vac down. So condensation would be liquid in my mind. Tiny particles in the refrigerant that would cause the rapid bouncing. So thats when i was saying when liquid would go through the compressor.


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