What is the function of a compressor?

I learned that the funciton of a compressor in a heat pump system is to compress the gas, into compressed gas, not liquid. Actually, I was very specifically advised that the gas does not become liquid until it is condensed. So, this NACHI question is confusing:

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You are trying to convert low temperature, low pressure gas to high temperature, high pressure gas. So it is part of the process which makes it a correct answer.

You are correct that a compressor should not and can not pump a liquid. It will destroy it eventually.

It does force Freon (improper terminology) into the evap coil, before the metering device. The metering device causes a huge pressure drop which causes it to flash off and cool the liquid refrigerant which enters the evaporator as a cooled liquid where it absorbs heat from the air and turns to a vapor. Back to the compressor to be compressed.
But that is “Not the Best answer”

The compressor also warms the cool low pressure gas as it compresses it and adds “Heat of Compression” to it as well. Still, “Not the Best Answer”.

As for warming a cool liquid; the only cool liquid is in the evap coil. A compressor sucks as well as pumps. So is effect, it does warm up cool liquid till it all flashes off in the evap coil.

Sounds like your having a fun time with this training! :wink:

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The question seems wrong. “condensor” makes more sense for the answer given.

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Yes, to a gas, not to a liquid. The answer states “liquid” even though it’s not liquid. So what is it that makes it a correct answer?

If this is the only correct answer then why is it not the best answer? All the other options are clearly incorrect.

Yes, it seems finding errors in the training materials is a great way to study. It gives me motivation to investigate everything more. The problem is that I have a pool of over 4000 questions to investigate and not enough years left in my life to do it all. I’m going to have to challenge the exam at some point without having all the answers.

It is not the best answer, BUT it is the best answer GIVEN.

I don’t want to belabor the point but the gist of my question is if the best answer given can be a wrong answer?

It seems to me that in this case it is not simply the best of the bad answers, it’s simply wrong. So how can a statement that is wrong be the best answer? Or is it possible I’m missing something? Is it possible that the compressor does in fact convert gas to liquid? That would be very insightful for me to lean that.

Or, maybe I need to apply occam’s razor? Maybe the question used compressor when it was supposed to be condenser?

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The answer is not “simply wrong.” Compression is part of the condensation process of refrigerants. Water will condense at atmospheric pressures because liquid is its natural state (at most of the earth’s temperatures). Refrigerants natural state at atmospheric pressures is a gas.
In order to condense into a liquid (for nominal heat transfer) it must be compressed. I believe one of the posts already pointed this out. It is a required part of the process…

I have a sense that you are getting very close to untangling this for me but I’m still confused about how it can be stated as true that a compressor converts gas to a liquid. I can’t find anything that supports that notion. Everything I’ve read contradicts that statement. I’ve read that the compressor actually heats up the gas which further activates the molecules which by definition makes them more gaseous, not more liquid, even if they are made liquid at some other point in the process. It doesn’t seem to be true that it’s the compressor that makes them liquid. Is this just one of those things we accept as true because it makes it easier to explain even if it’s not actually true?

I’m not sure what your confusion is. Without compression there is no condensation of a refrigerant. You can bicker all you like about the accuracy of the answer required, but it is the best answer given and for a rudimentary explanation of the process works just fine. Total comprehension of the physics involved is not needed nor are you being tested at an advanced level.

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Ok, I don’t have to dig further than that. I still think the statement is wrong and it’s hard for me to choose an answer that is clearly wrong, but I wrote the exam now so it’s not so important anymore.

Instead of arguing with @rkenney just look it up and read about it.

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Well, it’s usually people’s thinking that gets in the way of making a decision!

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What do you mean by arguing with @rkenney? I’m simply trying to understand something that seems confusing to me. I appreciate everyone who’s contributed to my posts because the dialog has brought a great deal of clarity but some things still remain confusing and I can’t pretend I get it.

What do you mean by “look it up” when I’ve stated clearly that I have looked it up. I spent a ton of time investigating every question I’ve posted and in this case I have found more references to say a compressor does not and can not convert gas into liquid than I have to say it does or even can convert gas to a liquid. I know that the gas is converted to a liquid in the process but is it the compressor that does it? I don’t think so but I’ll investigate that reference you posted. I’m here to learn but learning is not the same as blind acceptance of whatever someone tells me even if they are smarter than me.

Here’s my question back to you though, is this forum not the place for inspectors to discuss these topics and ask for clarification when we don’t understand, even independent of other research, even if we never did other research? I was told that is exactly what this forum is for. New inspectors should be able to find answers to all of these questions on these forums without searching elsewhere. But that won’t happen if people are not asking these questions on this forum. I’ve received several responses from people who have had similar questions as me so I’m confident my posts, my questions and my requests for clarification are a waste of forum resources.

Ok, semantics. The conversion happens in the condenser, but the pressure comes from the compressor.
image

So, what makes it happen?

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Yes, that’s why I posted the question. I think the statement should read condenser, not compressor. But I can understand why the answer to this question would be more obvious to people who have more experience with split systems. To all of you it’s just semantics, but to me I’m really digging in deep to understand it all and that’s what makes this question tough to swallow.

I really appreciate all the dialog. It’s helped me understand the process a lot better.

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Yes, I suspect you are probably correct in this case. But the dialog has challenged me to learn more and learn better.

Thank you all for all your input: @dandersen, @tglaze, @rkenney and @bcawhern1

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You (or anyone) could spend months learning HVAC theories, the laws of thermal dynamics, phase change, the methods of operation inside of heat pumps or A/C units, etc.

Only the most basic of concepts are typically addressed in a general home inspection, and many training or instructional guides just scratch the surface.
It’s been my experience that many training courses have some level of watered-down or diluted question that might be worded oddly, but the basic concepts are still there.

The inspectors that post here didn’t write the training guides, so specific test questions that are confusing should be sent to the correct department or person.

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David, FWIW, I have seen factual errors elsewhere in 'nachi content. I recently saw this link, which has (or had) the following statement:

“Regardless of the vent type [B or L], InterNACHI inspectors may check for the following defects:
• violation of roof clearance requirements. All metal vents must terminate at least 2 feet above the roof surface and anything within 10 feet of the vent, such as the crest of a roof ridge;”

The part about 2 feet simply isn’t true, and I alerted them about it and it will be corrected at some point, if it hasn’t been already.

More recently, a link to this video appeared in a FB forum, with the following description:

“…he performs a home inspection according to the InterNACHI® Standards of Practice. From top to bottom, and inside and out, Ray covers the SOP step by step…”

If you watch the whole 90+ minutes you might have questions like I did:
“[Nick Gromicko] Was that the entire inspection (aside from not showing every bathroom)? Were all of the InterNACHI standards of practice included and described? Also, was the inspection done in the inspector’s normal flow and process? Will you post the written report for that inspection?”

and got the following answer:
“No, it isn’t a course. It’s just an insight into how Ray does his inspections. He’s been doing them for decades and some of his students asked to see him in action.”

To which I suggested changing the description to say something like, “Here’s a sample of a few things in the 'nachi SOP” because it appeared that it was meant to be a full inspection. And because the guy says at the end thanks for watching the SOP inspection course…

My point is that there may be numerous other such issues. So, your questions about the questions are great, and might uncover similar things to be corrected.

Funny thing about a ‘compressor’ is it’s just a pump. The compression occurs when it pumps into a restricted space. Anyone who’s ever rebuilt an air compressor knows this. We can also pump water the same way AND raise its pressure. My pressure washer does just that. The key to understanding an air conditioning system or heat pump is getting a handle on temperature - pressure relationships.

It’s not a may be, it’s a “there are” throughout all of InterNACHI’s courses. Errors, misinformation, and questionable descriptions. Don’t get me wrong the majority of the courses are good, but do not limit your education to InterNACHI alone there are many outside sources. Especially when you question something, it’s good to look elsewhere for verification.

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