Measuring Superheat

[Mastercool]

Hello All

Living at the Victoria Falls in Zimbabwe means that I have great difficulty in obtaining any spares or measuring instruments. I have inherited a problem with a 24' Cake Display unit in a local supermarket and need to accurately measure the "Superheat" I reply on "Carriers" from other countries to bring spares etc into my part of the world. He as found an "Infa Red Digital" Thermometer which is accurate up to 1% of 1 degree. However, I have just read that an Infa Red Device should no be used. Please comment. Further, the pipe run for this unit is +/- 20 mts. It runs on R22. Any advice on how best to measure Superheat, will be gratefully received and can an Infa Red Digital Thermometer be used?

Many thanks

Errol

[HeathT]

Hi Errol,
I am also zimbabwean but living in the uk now. I believe you can use an infrared thermometer but just wrap the section of pipe you are measuring temperature from with some matt insulation tape to prevent the infrared beaming of the pipe. Ideally the most accurate would be a pipe clamp and probe that straps onto the pipe to give you the reading.

[nike123]

Compare your IR measurements with conventional measuring device. If accuracy and repeatability of IR thermometer satisfy your criteria and usage, then I don't see reason to not use it.
Be aware of spot size and emissivity of IR thermometer.
http://us.fluke.com/virtualdemos/SpotSize/spotsize.aspx

[coolhibby1875]

hi all it never seases to amaze me how many times on this forum someone asks the supaheat question,i have worked in the supermarket enviroment for 17 years and have done most aspects within the supermarket enviroment commissioning included,in every brand of supermarket except asda and other than using electronic controllers that measure supaheat for the operation of electronic expansion valves i have never worried about supa heat.
i am not having ago mastercool for asking the question but it seems to me that to some people just think supa heat is the be all and end all of every thing, i have read on here people ask questions like a compressor keeps tripping and people replying with something like what gas you using and whats the supa heat like that would have anything to do with a compressor tripping sorry had to get that of my chest as the magical supa heat question arrises here every other day and once again im not personally having a go at you mastercool.

[nike123]

hi all it never seases to amaze me how many times on this forum someone asks the supaheat question,i have worked in the supermarket enviroment for 17 years and have done most aspects within the supermarket enviroment commissioning included,in every brand of supermarket except asda and other than using electronic controllers that measure supaheat for the operation of electronic expansion valves i have never worried about supa heat.

That doesn't necessary mean that you are having good practice.
If you don't know superheat, you then don't know for fact what is happening in evaporator. You only guessing.
But if you like your way of doing things, then proceed!


i am not having ago mastercool for asking the question but it seems to me that to some people just think supa heat is the be all and end all of every thing, i have read on here people ask questions like a compressor keeps tripping and people replying with something like what gas you using and whats the supa heat like that would have anything to do with a compressor tripping sorry had to get that of my chest as the magical supa heat question arrises here every other day and once again im not personally having a go at you mastercool.

I will give you one example when superheat have something to do with compressor tripping.

If you have high superheat than you have also high compressor discharge temperature and that could trip compressor overload protection.

So you see that there is something to do with superheat.

[Magoo]

Hi mastercool.
Please define which super heat you want to check. a/ evaporator superheat or b/compressor suction superheat.
With most IR thermometers I have seen the manufacturer quotes and accurrecy range of 1 % of operating scale. Say -100 > + 200 equals a 3 degree variance, plus they are subject to ambient temps., like in a freezer the go awol. I use one, but for accurate readings prefer a Fluke twin scale with K ohm sensors, even they go wierd with low ambient temps as well.
Testing evap superheats, years ago I found info published by Kuba from Germany that dispelled all the rule of thumb trype taught at college.
Quote "the suction superheat is measured by reading the air on temp and reading the suction pressure at suction header and converting to temp, the suction gas super heat is calculated as 60>70 % of the system TD., ok the TD is air on versus evap actual evap temp in coil. Works a treat at any system condition, not necessarily at design temp, any adjustments to TX valve wait 15 minutes for TX vav to stabilize, Forgot to mention the suction line temp reading at thermo bulb

[Gary]

hi all it never seases to amaze me how many times on this forum someone asks the supaheat question,i have worked in the supermarket enviroment for 17 years and have done most aspects within the supermarket enviroment commissioning included,in every brand of supermarket except asda and other than using electronic controllers that measure supaheat for the operation of electronic expansion valves i have never worried about supa heat.
i am not having ago mastercool for asking the question but it seems to me that to some people just think supa heat is the be all and end all of every thing, i have read on here people ask questions like a compressor keeps tripping and people replying with something like what gas you using and whats the supa heat like that would have anything to do with a compressor tripping sorry had to get that of my chest as the magical supa heat question arrises here every other day and once again im not personally having a go at you mastercool.

Superheat is a useful diagnostic tool... nothing more and nothing less... and like any good tool, when used properly it makes the job easier. You can diagnose the system without it, but why would you want to?

[750 Valve]

hi all it never seases to amaze me how many times on this forum someone asks the supaheat question,i have worked in the supermarket enviroment for 17 years and have done most aspects within the supermarket enviroment commissioning included,in every brand of supermarket except asda and other than using electronic controllers that measure supaheat for the operation of electronic expansion valves i have never worried about supa heat.
i am not having ago mastercool for asking the question but it seems to me that to some people just think supa heat is the be all and end all of every thing, i have read on here people ask questions like a compressor keeps tripping and people replying with something like what gas you using and whats the supa heat like that would have anything to do with a compressor tripping sorry had to get that of my chest as the magical supa heat question arrises here every other day and once again im not personally having a go at you mastercool.

I completely agree with nike 123, suction superheat is VERY critical in some applications (like LT R22 where a lower superheat aids in keeping discharge temps down and also oil from breaking down and also reduce power consumption), download coolpack and plot some enthalpy diagrams - this may help you to realise how vital a correctly operating system is. Superheat also has a large bearing mass flow rates that any given compressor can move around a system. Pushing evap superheats to a minimum in a supermarket environment has massive gains, if all valves were running 15K superheats then you'd be struggling with case temp unless you lowered the rack SST, run the same system with 3K superheats and suddenly not only is case performance better (as you are maximising evap usage) but quite often you can LIFT the SST above even case manufacturers specs... or even better float the suction up as required.

Superheat is a vital way of measuring performance within the low side of a system.

[coolhibby1875]

high supa heat high discharge presure what happenend to using good old gauges and temperature to presure my point is when you start worrying about supa heat with actually putting thermometers on pipes ect well i feel people have way to much time and digging to deep looking for problems that simply dont exsist,therefore i personally feel that you should get a gauge on as many outlets as possible and go for there in reponse to 750 valve i agree all the things you say affect the good operation of a system but these are better achived through temperature to presure look after these and the supa heat will look after its self! so weather you feel the way i do things is good practice or not there is nothing worse when engineers are rushing around trying to make targets and being efficient at there jobs while other engineers are sitting around taking temps here and temps there with thermometeres clamped to pipes,
tweaking valves a third of a turn waiting 15 mins turning a quarter turn again waiting another 15 mins again and so on to discover the orrifice is a bit blocked or you have to change a expansion valves.
I know what type of engineer i would rather employ the 1 that has the highest output and is most efficient of course because he would probally have changed the valve strait away job done and be on his way to the next job,so i better end this rant up as im away to download some enthalpy diagrams.

[750 Valve]

So you'd be happy to employ someone to half commission a store? That way the next company that comes in there can point out to the customer just how little you actually did for the money you were paid. Makes perfectly good business sense....

Also a good service mechanic does not go adjusting TX valves willy nilly - this is the job of the commissioner to set each coil up to maximise its efficiency. 90% of the time a good service mechanic would pump down the case and pull the strainer for a look before adjusting, or maybe check the gas charge. But if you prefer then to just change a perfectly working valve as they know not how to check nor set superheat then I guess that is up to you. Once again good business sense....

Mate, if you think you can tell everything by a pressure guage then I tip my hat to you - obviously your guages function as some sort of crystal ball type arrangement because there is no way in hell that you can tell if a compressor is running high discharge temps by just a guage - it could be condensing at a perfectly acceptable pressure and be running horrendously high discharge temps - from a discharge and suction guage you wouldn't have a clue. Anyhow, seeing as you have just downloaded coolpack and ran a few scenarios you would know the effect high superheats have on a system now.

In this game a good mechanic relies on as much info as he can, a bad one just changes the compressor, bills the customer and moves onto the next store. Sometimes people get jaded due to the long hours and fall into a rut of just stopping the alarm and getting out of the store, if it gets that way then you either slip into mediocrity get a desk job.... or at least a change of scenery.

Sorry if I offend but it attitudes such as the one you have exhibited give good mechanics that genuinely care to learn or go out of their way to help a customer a bad name. Just because you feel the need not to offer the full extent of your services does not mean that anyone else should. If the original poster wants to check what superheat his system has then let him, he will likely gain more knowledge on his system's operation and be able to validate or discount some theories he has as to the fault and be one step closer to providing an answer to his client.

To answer the original poster - as suggested if you run a comparison between IR thermometer and an other type and find it to be consistent and accurate then it may work. Personally I do not like them, I only use them as a quick indicator. I prefer a type K thermocouple on a Fluke 54/II thermometer if I really must know the exact temp. I also use a standard digital thermometer that is sold over the counter at refrig and AC outlets in Aus and it works pretty well too.

[nike123]

high supa heat high discharge presure

High superheat doesn't have any influence on high discharge pressure! On the other hand, high discharge temperature has been result of high superheat.

[Gary]

There are two separate issues here: Checking superheat and adjusting TXV's.

Checking superheat as a diagnostic tool is a very good thing.

Adjusting the TXV is almost always a mistake.

[750 Valve]

There are two separate issues here: Checking superheat and adjusting TXV's.

Checking superheat as a diagnostic tool is a very good thing.

Adjusting the TXV is almost always a mistake.

Its only a mistake as people do not discount all other avenues (gas charge, liquid flashing, blocked strainers, etc) before adjusting.

[Mobbsy]

download coolpack and plot some enthalpy diagrams - this may help you to realise how vital a correctly operating system is. Superheat also has a large bearing mass flow rates that any given compressor can move around a system.

Superheat is a vital way of measuring performance within the low side of a system.

Absolutely 750, one can clearly plot and document the increase in volume of the vapour as it superheats, and as you have stated it has a direct effect on how much refrigerant can be circulated per time interval, due to the greater volume of refrigerant per kilogram within the cylinder (assume reciprocating).
Although we don't expect each other to plot pressure enthalpy diagrams at every service call, I feel the charts ability to demonstrate the effects of system characteristics such as excessive suction superheat should not be underestimated.
Coolhibby 1875's point of utilising gauges in conjunction with a pressure temperature chart is an excellent point. It enables a proper understanding of any operational plant, but just as important is the knowledge and ability to measure temperatures for the purpose of calculation against saturated conditions, in determining not only superheat, but also sub-cooling.
We should also remember that a hermetic and semi-hemetic compressor rely on the suction vapour to cool the motor winding's, an unacceptably high suction temperature could possibly lead to a compressor tripping, due to winding damage.

I believe that once you have a firm and correct understanding of the refrigerant's state and condition within a vapour compression system and also how to determine these particular charateristics, a technicians instinctive diagnostic skills and problem solving skills are far superior to someone who does not have this knowledge.

Mastercool you have stated that you are the fortunate beneficiary of an existing problem with a cake cabinet, out of curiousity why do you believe the problem is related to the superheat, and what are the symptoms?

[Slatts]

:off topic:gedday coolhibby.
We need more people like you in the trade!
Blokes like you make our customers appreciate the rest of us more.

Keep up the good work cobber.

[Mastercool]

Thank you all for all the help. I was asking for help with refernce to the use of an Infa Red Digetal Thermometer. However, I shall gladly give all the symtoms that are pointing, in part to the superheat. You guys are simply not going tp believe the rest of the story. In the first place I did not do the installation. It was only after four compressor failours, after the initial installation that I was asked to come in. Before I undertook the istallation of a further new Condenser unit. I throughly inspected the whole installation, well my my my!!!. The orogional technician had not fitted a solinoid valve. The electrical cables were lying coiled up over each other and intertwined with the PT sencor cable, which was of 3 core fexable cable. Not good. Anyway after throughly flushing the complete unit using 141b flushing liquid, I fitted the compressor. After doing all the checks, pressure etc and after a 24 hour Vacuum, the unit was fired up. All went well. The pressures are ok the amperage drawn is 1amp below the rate AMPS and the colling effect is excellent. However, the suction line begines to "FROST UP" right up to the compressor, with the "Sight Glass" still showing an excessive amount of bubbles. In my part of the world the first thing at a local operator would do is to "Adjust the Suerheat" It is not uncommon to find the supereat adjustment screw on the TX valve, FULLY OPEN. As I am not finished with this unit yet, I stall need to see, if in fact, a superheat adjustment had been made and without the necessary accurate thermometers available, I asked the forum for advice on the use of the Infa Red device. I shall be most grateful if any further advice, re this problem can be given. With many thanks

Errol

[nike123]

Thank you all for all the help. I was asking for help with refernce to the use of an Infa Red Digetal Thermometer. However, I shall gladly give all the symtoms that are pointing, in part to the superheat. You guys are simply not going tp believe the rest of the story. In the first place I did not do the installation. It was only after four compressor failours, after the initial installation that I was asked to come in. Before I undertook the istallation of a further new Condenser unit. I throughly inspected the whole installation, well my my my!!!. The orogional technician had not fitted a solinoid valve. The electrical cables were lying coiled up over each other and intertwined with the PT sencor cable, which was of 3 core fexable cable. Not good. Anyway after throughly flushing the complete unit using 141b flushing liquid, I fitted the compressor. After doing all the checks, pressure etc and after a 24 hour Vacuum, the unit was fired up. All went well. The pressures are ok the amperage drawn is 1amp below the rate AMPS and the colling effect is excellent. However, the suction line begines to "FROST UP" right up to the compressor, with the "Sight Glass" still showing an excessive amount of bubbles. In my part of the world the first thing at a local operator would do is to "Adjust the Suerheat" It is not uncommon to find the supereat adjustment screw on the TX valve, FULLY OPEN. As I am not finished with this unit yet, I stall need to see, if in fact, a superheat adjustment had been made and without the necessary accurate thermometers available, I asked the forum for advice on the use of the Infa Red device. I shall be most grateful if any further advice, re this problem can be given. With many thanks

Errol

I would suggest that you first check at what position is valve regulation stem and to wind it back to factory adjustment for that valve. Then proceed with charge adjustment according to subcooling. Superheat will be high until cooled space reach near target temperature and you could expect bubbles in sight glass before valve, until your cold room is near target temperature, because when you have high evaporator load TXV could be fully open and still not maintaining adjusted superheat.
Only when you have cold room near designed temperature and condensation temperature near designed temperature and sufficient subcooling you could adjust your TXV to desired superheat. Do not care much for bubbles if you have correct subcooling and low pipe temperature difference from condenser to TXV (max. 2K).

Ice on the pipe doesnt mean that liquid is present in suction, it only mean that pipe is at temperature lower than 0°C. Only if you measure 0K superheat your compressor is at danger.


When measuring with IR thermometer, always apply one layer of black electrician insulating tape at measured pipe (and adjust emissivity at 0,95 if it is adjustable) and measure temperature from 3-5 cm from pipe bearing in mind position of IR sensor in relation to pipe, and not where laser spot points.
To be safe at superheat adjustment, it is better to adjust it, for example, at 5K then at 3K if you are relying at such "inaccurate" instrument.

I put inaccurate in quotation marks because question is how accurate are our gauges.

And one more thing. When I change compressor after burn-out or mechanical failure, which is priced more than 1000€ I change also TXV, regardless of his condition.

[Gary]

In order to properly evaluate the system, we need the air in/air out temps for both coils, the suction line and liquid line temps, and the pressures.

I normally use an IR thermometer for locating hot spots in electrical panels and nothing else. I would prefer any other type of thermometer for pipe temps. I have little faith in IR thermometers... but perhaps others have had better results with them.

[coolhibby1875]

Hi slatts there must be something in the water down under that makes the engineers down under think they are better than everyone else. But i guess by your post you must be 1 of these engineers that thinks nothing of sitting around in the same store all day, even if you think the customer appreciates i bet your boss doesnt unless its a pay as you go, then your boss will be loving it, but then your customer wont when they receive there bill, when they realise they are paying a fortune for a engineer that spends half the day in the canteen drinking coffee and downloading enthalpy charts but hay everyone to thier own!

[nike123]

Hi slatts there must be something in the water down under that makes the engineers down under think they are better than everyone else. But i guess by your post you must be 1 of these engineers that thinks nothing of sitting around in the same store all day, even if you think the customer appreciates i bet your boss doesnt unless its a pay as you go, then your boss will be loving it, but then your customer wont when they receive there bill, when they realise they are paying a fortune for a engineer that spends half the day in the canteen drinking coffee and downloading enthalpy charts but hay everyone to thier own!

You guys could do that on private messages, since original poster, nor rest of other constructive posters, are not interested in your fight!:(

[750 Valve]

I normally use an IR thermometer for locating hot spots in electrical panels and nothing else. I would prefer any other type of thermometer for pipe temps. I have little faith in IR thermometers... but perhaps others have had better results with them.

I agree 100%, I am not a massive fan of them. I would use most other forms of temp measurement before an IR.

And coolhibby, we aren't any better down here. I am not gonna get into an argument about how to be a fridgie, I feel i have said all I need to.

[Slatts]

I concur. On both points.
I'm not a big fan of IR thermometers for accurate work.
And Australia has it's fair share of blokes in the field who should be working in a field.
And I apologize if my half smart comment offended anyone.

[nike123]

I concur. On both points.
I'm not a big fan of IR thermometers for accurate work.
And Australia has it's fair share of blokes in the field who should be working in a field.
And I apologize if my half smart comment offended anyone.


This is for discussion purpose only, I am not offended at all.:)

Please answer honestly this questions.
Do you use digital pressure gauge? If yes, what is model#.
If not, than you must be using analogue pressure gauges?
What is accuracy of your pressure gauge when you reading superheat and do you calibrate it regularly?
What is gauge diameter?
Do they have mirror at scale for correct angle of sight when reading pressure?
What class are they?
Are they oil filled?

[Mobbsy]

Thank you all for all the help. As I am not finished with this unit yet, I stall need to see, if in fact, a superheat adjustment had been made and without the necessary accurate thermometers available, I asked the forum for advice on the use of the Infa Red device. I shall be most grateful if any further advice, re this problem can be given. With many thanks

Errol
I employed the use of an infa red themometer on only three occasions, after which I did not use them again, but this was a number of years ago. This would answer your original question mastercool from my point of view and personal experience only, the quality may have improved since then, but I have stuck with what I trust over the years.

Gary has made a valid request of needing to know the systems running conditions in order to better diagnose any problems. Your intuitive instict to further evaluate the unit is wise, considering it is now running on its fourth compressor; on what I assume is a relatively new system.

Matercool have you used the IR themometer that you have on hand, and if so what was evaporator superheat? total suction superheat? subcooling provided by condenser?subcooling before TX?

As it has already been pointed out there is little need to enter into an argument, but a point was made of the different tools and charts available to any refrigeration mechanic, which we all should be aware of. There is no doubt that any problem should be solved starting from simplistic knowledge to more complex concepts and not the other way around.

Anyway, it's time for my nightly glass of water which the Australian government is kind eneough to add fluoride to, in order to strengthen my teeth.

[Slatts]

Please answer honestly this questions.
Do you use digital pressure gauge? If yes, what is model#.
If not, than you must be using analogue pressure gauges?
What is accuracy of your pressure gauge when you reading superheat and do you calibrate it regularly?
What is gauge diameter?
Do they have mirror at scale for correct angle of sight when reading pressure?
What class are they?
Are they oil filled?

Analog 2" non oil filled gauges.
accurate to within a pound or so.
I also own an IR thermometer that I use to check such things as sump temperature, quick and dirty discharge and suction temperatures and the like.
I rarely check superheat on a normal callout (speaking of which, there goes my bloody pager. That's the 9th callout since Friday night) unless it's a system I've not worked on before or I have reason to suspect it is out of wack. at which point I drag out the Fluke digital thermometer.

[nike123]

Analog 2" non oil filled gauges.
accurate to within a pound or so.
I also own an IR thermometer that I use to check such things as sump temperature, quick and dirty discharge and suction temperatures and the like.
I rarely check superheat on a normal callout (speaking of which, there goes my bloody pager. That's the 9th callout since Friday night) unless it's a system I've not worked on before or I have reason to suspect it is out of wack. at which point I drag out the Fluke digital thermometer.

So you are disputing your IR thermometer readings and don't dispute your gauge reading.
From your answer I concluded (correct me if I am wrong):
You did not ever calibrated your gauge in agency (establishment) for that purpose or with calibration instrument, and still think that is accurate for temperature reading (that is why we use it, to get saturation temperatures).

That diameter of gauges gives accuracy usually 2-3% of scale range. Scale range for R22 gauge for low pressure is usually -10 to 140 psi. That is 150 psi range.
That is 3-4,5 psi accuracy (not 1 pound)! At around 20 psi pressure that is error of 2°-3°C. Similar as low quality IC thermometer.

http://www.yellowjacket.com/HVACRProducts.asp?t=HVACR&l=5&c=40&p=112

Next is scale resolution!
At 20 psi range resolution is low and you cannot precisely tell exact psi value. It is about 2 psi resolution. Ad to that needle thickness and that number goes up.
That is additional 1-2°C error for resolution. We are now already in range of 4-5°C total reading error.
At same time most IR thermometers have resolution of 0,1°C
Ad to that a fact that practically nobody ever calibrate their gauges in agency or with calibrator, you get picture of actual accuracy of your gauges.
Then add to that fact that many times we read pressure at compressor suction and neglect pressure drop to point of temperature measurement and things looks little funny.
We judge accuracy of IR thermometer while our gauges are as inaccurate as they could be.

I dont say that is beter to use IR thermometer than termocuple, but I say that if we want accurate reading that all our instruments should be equaly precise.

And I few times said this:

Compare your IR measurements with conventional measuring device. If accuracy and repeatability of IR thermometer satisfy your criteria and usage, then I don't see reason to not use it.
Be aware of spot size and emissivity of IR thermometer.
http://us.fluke.com/virtualdemos/SpotSize/spotsize.aspx

[slingblade]

Thank you all for all the help. I was asking for help with refernce to the use of an Infa Red Digetal Thermometer. However, I shall gladly give all the symtoms that are pointing, in part to the superheat. You guys are simply not going tp believe the rest of the story. In the first place I did not do the installation. It was only after four compressor failours, after the initial installation that I was asked to come in. Before I undertook the istallation of a further new Condenser unit. I throughly inspected the whole installation, well my my my!!!. The orogional technician had not fitted a solinoid valve. The electrical cables were lying coiled up over each other and intertwined with the PT sencor cable, which was of 3 core fexable cable. Not good. Anyway after throughly flushing the complete unit using 141b flushing liquid, I fitted the compressor. After doing all the checks, pressure etc and after a 24 hour Vacuum, the unit was fired up. All went well. The pressures are ok the amperage drawn is 1amp below the rate AMPS and the colling effect is excellent. However, the suction line begines to "FROST UP" right up to the compressor, with the "Sight Glass" still showing an excessive amount of bubbles. In my part of the world the first thing at a local operator would do is to "Adjust the Suerheat" It is not uncommon to find the supereat adjustment screw on the TX valve, FULLY OPEN. As I am not finished with this unit yet, I stall need to see, if in fact, a superheat adjustment had been made and without the necessary accurate thermometers available, I asked the forum for advice on the use of the Infa Red device. I shall be most grateful if any further advice, re this problem can be given. With many thanks

Errol

A reasonable surface thermometer is sufficient for this, along with a guage which is not damaged, and if the guage does not support the refrigerant used, then a comparator.
Attach the thermometer ( i use a velcro pipe wrap around ) to the suction (near the evap. outlet ) and attach the guage to the suction. i try to look for a superheat ( application dependant - suggest evap of 0 dec c to match follows ) of 7 to 14 deg c. If liquid floods back or your compressor, or it overheats, and if txv adjustment will not solve the problem, i would suggest the problem lies elsewhere( incorrect oraface/blocked drier ect). however give at least 5 mins before each adjustment and look again.
There may be other very obvious things to look for, poke your head round everything and you may surprise yourself. good luck.:)

[Slatts]

So you are disputing your IR thermometer readings and don't dispute your gauge reading.
From your answer I concluded (correct me if I am wrong):
You did not ever calibrated your gauge in agency (establishment) for that purpose or with calibration instrument, and still think that is accurate for temperature reading (that is why we use it, to get saturation temperatures).

That diameter of gauges gives accuracy usually 2-3% of scale range. Scale range for R22 gauge for low pressure is usually -10 to 140 psi. That is 150 psi range.
That is 3-4,5 psi accuracy (not 1 pound)! At around 20 psi pressure that is error of 2°-3°C. Similar as low quality IC thermometer.

http://www.yellowjacket.com/HVACRProducts.asp?t=HVACR&l=5&c=40&p=112

Next is scale resolution!
At 20 psi range resolution is low and you cannot precisely tell exact psi value. It is about 2 psi resolution. Ad to that needle thickness and that number goes up.
That is additional 1-2°C error for resolution. We are now already in range of 4-5°C total reading error.
At same time most IR thermometers have resolution of 0,1°C
Ad to that a fact that practically nobody ever calibrate their gauges in agency or with calibrator, you get picture of actual accuracy of your gauges.
Then add to that fact that many times we read pressure at compressor suction and neglect pressure drop to point of temperature measurement and things looks little funny.
We judge accuracy of IR thermometer while our gauges are as inaccurate as they could be.

I dont say that is beter to use IR thermometer than termocuple, but I say that if we want accurate reading that all our instruments should be equaly precise.

And I few times said this:
So then what would you have us do Nike? have our gauges and thermometers certified at the start of each call?
We're trying to optimize an analog negative feedback system.
Any thoughts on doing it purely from the suction temperature curve leaving the evap?

[nike123]

So then what would you have us do Nike? have our gauges and thermometers certified at the start of each call?
We're trying to optimize an analog negative feedback system.
Any thoughts on doing it purely from the suction temperature curve leaving the evap?

You miss my point.
I only wanted to describe how we easy take our gauges as some precision tool, and take actions upon their reading, without thinking how much they could be off from real condition in pipes.
In same time, we judge other tool who is equally or more precise then our gauges (when used correctly).
Of course that two low precision tools add to total error, and that is better when one of them is more precise.

And, I qoute myself again:

Compare your IR measurements with conventional measuring device. If accuracy and repeatability of IR thermometer satisfy your criteria and usage, then I don't see reason to not use it.
Be aware of spot size and emissivity of IR thermometer.
http://us.fluke.com/virtualdemos/SpotSize/spotsize.aspx

[chancie owens]

well if you dont have accurate superheat you run the risk of overheating your compresor or flooding it out the system wont last and just as bad wont operate right.

[Phase Loss]

After 4 compressor failures, you would want to know how these compressors failed. If they all had broken valves, pistons, connecting rods, then it would be quite clear that they have been trying to compress liquid.

I have not herd good things about IR for checking pipe temperatures. IR works well on flat surfaces that are non reflective. A copper pipe is curved and reflective, which could cause your IR beam to bounce all over and give random readings. But I have also heard that wrapping the pipe with black tape and using a high end IR could possibly work.

I use a digital set of guages (digi cool) and a Fluke 52 k-type probe that usually gets calibrated once a month in an ice bath to make sure it reads 32* and also checked in boiling water to make sure it reads 212*. to check superheats.

If you have frost going back to the compressor, this does not mean floodback. all it means is that your suction line is below dew point/frost point.

You would need to check suction superheat and would want to see in the no lower than minimum 20* superheat. as for maximum suction superheat, you would not want to see your discharge line temperature 6" away from the compressor exceed 250*.

It would be nice to know why the last 4 compressors died:eek: