reading your guages

[thewoodman]

I have an ongoing argument with my boss about reading the gauges. I say the green scale for R22 tells me the saturation temp. of the refrigerant. He says it is the actual temperature of the freon in the suction line. I say no it is the temperature at which the freon saturates at the corresponding pressure. Pressure temperature relationship. Ok.. he tells me he as two years of AC college and I can't convince him different. He still maintains it is the temperature of the freon. AM I not understanding this or what??

[Dad]

To make this argument quick and easy, go to your gauges and look at the 100 lb mark. You will see that 100 is about 60* for R-22 on both sides.

Your gauges do not measure saturated temperature.

That is done by using formulas on subcooling and superheat. Such as subcooling + refrigerant temperature = saturated temperature of liquid line. Superheat + refrigerant temperature = saturated temperature of suction line.

If you need proof... I think I can find an old link somewhere that you can print from RSES.

[sadlier]

Unfortunately the boss is always right... even when he's wrong. The green scale is the saturation temperature (boiling temperature) at sea level. The thermomter tells what the actual refrigerant temperature is.

The saturation temperature is the temperature at a given pressure in which refrigerant temperature will not rise any more without changing states (IE from liquid to vapor). Lusker meant to say Subcooling = saturated temperature - refrigerant temperature, and Superheat = refrigerant temperature - saturated temperature.

[Edited by sadlier on 06-11-2005 at 11:52 AM]

[beenthere]

Originally posted by sadlier
Unfortunately the boss is always right... even when he's wrong. The green scale is the saturation temperature (boiling temperature) at sea level.

Saturation temp at that pressure in psig.

[Edited by sadlier on 06-11-2005 at 11:52 AM]

[Dad]

sadlier

Look at your equation and look at mine. They both say the same thing.

You are looking for subcooling and superheat. Reverse your equation and I am looking for saturated temperatures.

[phosgene]

I agree with you woodman. the pressure on the low side gauge corrospondes with the saturated refrigerant temp in the evap coil. the pressure temp relationship only exists at saturation which occurs in either coil, not the suction line.in the suction line the temp would be greater as you would have added super heat. the scale on the gauges is the same as the scale on a pt chart, they are just useing the most popular gases and saving you from having to pull out the chart

[Edited by phosgene on 06-11-2005 at 12:19 PM]

[Dad]

There is only one problem with my perfectly logical post.

You can't find superheat or subcooling unless you have a saturated temperature value, so that would make the PT chart or gauge chart your saturated temperature wouldn't it.

OK... just call me a dumb a$$.

[thewoodman]

this is what I am trying to say, that the gauges don't tell you the temperature, they give the given temp. of the refrigerant when it changes state,(from liquid to vapor or vise versa) at a given pressure. Am I correct in saying it is the boiling point of the refrigerant at a given temp. Example.. suction pressure on r22 at 55psi would mean about 30 or 32 temp the refrigerant will begin to boil. Which is not saying the refrigerant is 32 degrees. And this is my agrument with him, when I was charging a unit he said the refregerant in the suction line where my gauge is reading 55 the r22 in that line is 32 degrees. Which I believe is wrong. The actual temp. of the line say is 42 - 32 equal 10 degrees of superheat. It is 10 above the saturation point at this pressure. I believe this is a fundemental law of Physics. Now either I am wrong or he is..

[beenthere]

Lusker,

Are you doing you company paper work, and posting here at the same time.

[Dad]

Originally posted by beenthere
Lusker,

Are you doing you company paper work, and posting here at the same time.

shut up

so are you....

[thewoodman]

I just read your post lusker and I appreciate your input..post 1393 makes simple since doesn't it.

[beenthere]

Originally posted by thewoodman
this is what I am trying to say, that the gauges don't tell you the temperature, they give the given temp. of the refrigerant when it changes state,(from liquid to vapor or vise versa) at a given pressure. Am I correct in saying it is the boiling point of the refrigerant at a given temp.



It is the temp at which it will change state either from a lquid to vapor, or vise versa. Depending if your reading saturated vapor or liquid.




Example.. suction pressure on r22 at 55psi would mean about 30 or 32 temp the refrigerant will begin to boil. Which is not saying the refrigerant is 32 degrees. And this is my agrument with him, when I was charging a unit he said the refregerant in the suction line where my gauge is reading 55 the r22 in that line is 32 degrees. Which I believe is wrong. The actual temp. of the line say is 42 - 32 equal 10 degrees of superheat. It is 10 above the saturation point at this pressure. I believe this is a fundemental law of Physics. Now either I am wrong or he is..

You would be right that the line temp would be higher.




Show this post to your boss, and let him give his reply.

[Steve Wiggins]

Woodman want some REAL GOOD advice? Go to your boss and apologize for disagreeing with him. Tell him he is right and you are wrong. Tell him you feel like a complete moron.

If you tell him he is wrong YOU LOSE!

[mdman]

Originally posted by thewoodman
I have an ongoing argument with my boss about reading the gauges. I say the green scale for R22 tells me the saturation temp. of the refrigerant. He says it is the actual temperature of the freon in the suction line. I say no it is the temperature at which the freon saturates at the corresponding pressure. Pressure temperature relationship. Ok.. he tells me he as two years of AC college and I can't convince him different. He still maintains it is the temperature of the freon. AM I not understanding this or what??

Like most, your "boss" attended school but either missed the point or was taught by an "experienced" instructor who de-emphasized such topics in the interests of being "practical".

Unless you are deriving compression ratio or setting pressure controls accurately then the only useful information on the gauge is the sat temp (even more true when you work with several refrigerants).

Most of the heat absorbed in the evaporator, and rejected in the condenser are latent exchanges so the respective sat temp represents the temp at witch the refrigerant is exchanging heat. This is mucho impport-o.

I do get pissed every time someone makes reference to head or suction pressure because they are missing this major point. The top techs out there will not flame this thread and they are all nodding right now.

<snip>
He says it is the actual temperature of the freon in the suction line.
</snip>
1. Because of what I said, it is very close to the actual temp of the refrigerant at saturation *inside the evap coil* before super heating occurs.
2. If it was the actual temperature of the freon **in the suction line**, this would only be true if the saturation point extended out side the evaporator (i.e. liquid flood back) and into the suction line which is bad ju ju.

If the state exams where worth a crap your "boss" would not have the license and perhaps you would (other real qualifications permitting). You could then bust him down to installer until he learned something (two years of AC college notwithstanding).

I have not fully discussed the subject here. It is also possible that your "boss" understands it better than your question indicated but has failed to communicate the distinction between suction line and evaporator.

BTW, the P-H chart never lies.

[Edited by mdman on 06-11-2005 at 02:14 PM]

[Dad]

Charging Residential Air Conditioning by - Roger D. Holder, CM, BSME

Ya'll enjoy this Saturday afternoon's reading.

[thewoodman]

everyones input is great. All advice is good. Thanks guys. I don't think I will tell him he is wrong. But I don't think he understands what superheat is either. I tried to explain this by using water as an example and his reply was water is different than freon. He still uses his hand to feel for the suction line to determine if it is correctly charged. I believe in using a pt chart with the units mfg. suggestion. Again many thanks.

[hvac r us 2]

I worked for the same dealer for 15 years before I became a tech rep; him and I are very close.

He always had a sign on his door that read

RULE #1 THE BOSS IS ALWAYS RIGHT.
RULE #2 IF THE BOSS IS WRONG REFER TO RULE NUMBER 1.

Seriously though, it is sort of funny. If the suction gauge temperature represented the temperature of refrigerant in the suction line you would always have zero superheat! lol

[mdman]

Like most incumbent bureaucrats and enforcement agencies, there is no requirement to be right when you are in charge.

keep learning, do not listen to opinion, conjecture, or misinformation, pursue hard facts, go into business for your self, compete away your previous employers market share, laugh at him while he's greeting you on the way into Wal-Mart.

[mdman]

Originally posted by hvac r us 2
I worked for the same dealer for 15 years before I became a tech rep; him and I are very close.

He always had a sign on his door that read

RULE #1 THE BOSS IS ALWAYS RIGHT.
RULE #2 IF THE BOSS IS WRONG REFER TO RULE NUMBER 1.

Seriously though, it is sort of funny. If the suction gauge temperature represented the temperature of refrigerant in the suction line you would always have zero superheat! lol

I would not have worked there 15 min after reading such a pig eyed statement.

Hope your working in less of a communists state these days.

[Dad]