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dioshin
09-21-2011, 11:03 PM
quickly is what im after...... what is your methodology of quickly troubleshooting a refrigeration systems, lets say a walk in cooler? (not keeping temp), so far after 1 year of installing and 6 months service, and finished my first year of refrige school i came up with this method for speed, take ambient temp, step 1.check temp control for malfunction, 2. check/clean condenser coil and install thermometer on clean condenser, 3. touch compressor head hopefully its hot and look at sight glass, 4.if cold check site glass and check/clean evaporator, 5.if still cold compressor suspect and check evap fins and fan motor, 6. check/clean evap check all compressor electrics/capactors, check thermometer at condenser hopefully have 20f hotter than ambient or might be low charge 7. if short cycling check external overload, 8. still cant find issue attach guages and check/monitor/adjust tx valve and check superheat and subcooling and good time to check pressure control / if tx valve ok, 9.check for indication of leak, 10. if blended refrigerant recover with scale (maybe overcharged system), evac, nitrogen, evac again, charge to sight glass 4-6 hours job by this point. this seems to serve me well expecially on tiny under counter systems that you want to avoid putting guages on because youll suck out 30% of the charge and most times there critically charged cap tube systems. i guess my problem is im on my own, no help or guidance from other techs, and how do i know that a compressor is functioning 110% without completeing all this and finding out the compressor is weak? any ideas?

Tool-Slinger
09-23-2011, 08:28 PM
quickly is what im after...... what is your methodology of quickly troubleshooting a refrigeration systems, lets say a walk in cooler? (not keeping temp), so far after 1 year of installing and 6 months service, and finished my first year of refrige school i came up with this method for speed, take ambient temp, step 1.check temp control for malfunction, 2. check/clean condenser coil and install thermometer on clean condenser, 3. touch compressor head hopefully its hot and look at sight glass, 4.if cold check site glass and check/clean evaporator, 5.if still cold compressor suspect and check evap fins and fan motor, 6. check/clean evap check all compressor electrics/capactors, check thermometer at condenser hopefully have 20f hotter than ambient or might be low charge 7. if short cycling check external overload, 8. still cant find issue attach guages and check/monitor/adjust tx valve and check superheat and subcooling and good time to check pressure control / if tx valve ok, 9.check for indication of leak, 10. if blended refrigerant recover with scale (maybe overcharged system), evac, nitrogen, evac again, charge to sight glass 4-6 hours job by this point. this seems to serve me well expecially on tiny under counter systems that you want to avoid putting guages on because youll suck out 30% of the charge and most times there critically charged cap tube systems. i guess my problem is im on my own, no help or guidance from other techs, and how do i know that a compressor is functioning 110% without completeing all this and finding out the compressor is weak? any ideas?
I feel the lines. With the backs of my fingers because the skin is thinner for a quick check and if I get electrocuted I will not grab onto the line uncontrollably. again. Liquid line should be warm and suction cool. That usually points me in the right direction right away in case of a major failure component or issue.

In the case of a border-line failure, I pretty much start hooking up gauges and strapping thermal leads everywhere. If I service it on a PM schedule, the coils will be clean already. If it is a new animal, I am going to check everything top to bottom before I leave and I will not only fix the immediate problem but resolve other issues if there are any.

On small units without access to the refrigerant system, going by feel is far more important. Hands, ears, and eyes are better than any thousands of dollars worth of tools in many cases.

SwampTromper
09-23-2011, 08:46 PM
There are so many variables as to what can happen but upon first arrival try to get a rundown on symptoms and recent timeline and if available check sensor data and trends. From there check that it is cooling and moving heat, and that all components are on and running when in call. If so make sure evap and condenser are clean and hookup gauges. If not, start tracing problems in electrical circuits starting with main supply etc. then control supply etc. After that, things may take you to the borders of hell and back and spiderweb in too many directions to get into.

dioshin
09-27-2011, 08:25 PM
well it sounds to me like both you guys put your guages on real early in your diagnostics, if its a call for not keeping temp, now am i making a mistake by doing that at the end?
and the reason i ask is because, in my experience (which compared to a 4-5-licensed tech is limited), whatever your checking for with your guages theres tell tale signs of whats going on before you put them on, i only need my guages to reset a low pressure control if its set way to low, (usually) or check compressor valves if possible with correct service valves/king valve am i wrong? and im always quenched for time cause im in food service industry and these people (employers/customers) have no respect for refrigeration like they should, and im always finding half fast instalations, and extremely bad working units, for example walk in cooler with low pressure control set to cut out at 5f because evap coil plugged solid, and i get the call cause its frozen over. ask the owner if he knows why control is set 20 degress lower than it should and i get an "i dont know its always been that way".

and 1 more question what would you guys set condensing temp, when adjusting a water regulating valve? i've been setting at 105f is that correct?

jpsmith1cm
09-27-2011, 08:28 PM
Unless it is a critically charged system, I'm hooking up gauges very early in the troubleshooting process.

Once the compressor is running, I want pressures.

just_opinion
09-27-2011, 08:57 PM
quickly is what im after...... what is your methodology of quickly troubleshooting a refrigeration systems, lets say a walk in cooler? (not keeping temp), so far after 1 year of installing and 6 months service, and finished my first year of refrige school i came up with this method for speed, take ambient temp, step 1.check temp control for malfunction, 2. check/clean condenser coil and install thermometer on clean condenser, 3. touch compressor head hopefully its hot and look at sight glass, 4.if cold check site glass and check/clean evaporator, 5.if still cold compressor suspect and check evap fins and fan motor, 6. check/clean evap check all compressor electrics/capactors, check thermometer at condenser hopefully have 20f hotter than ambient or might be low charge 7. if short cycling check external overload, 8. still cant find issue attach guages and check/monitor/adjust tx valve and check superheat and subcooling and good time to check pressure control / if tx valve ok, 9.check for indication of leak, 10. if blended refrigerant recover with scale (maybe overcharged system), evac, nitrogen, evac again, charge to sight glass 4-6 hours job by this point. this seems to serve me well expecially on tiny under counter systems that you want to avoid putting guages on because youll suck out 30% of the charge and most times there critically charged cap tube systems. i guess my problem is im on my own, no help or guidance from other techs, and how do i know that a compressor is functioning 110% without completeing all this and finding out the compressor is weak? any ideas?


I feel the lines. With the backs of my fingers because the skin is thinner for a quick check and if I get electrocuted I will not grab onto the line uncontrollably. again. Liquid line should be warm and suction cool. That usually points me in the right direction right away in case of a major failure component or issue.

In the case of a border-line failure, I pretty much start hooking up gauges and strapping thermal leads everywhere. If I service it on a PM schedule, the coils will be clean already. If it is a new animal, I am going to check everything top to bottom before I leave and I will not only fix the immediate problem but resolve other issues if there are any.

On small units without access to the refrigerant system, going by feel is far more important. Hands, ears, and eyes are better than any thousands of dollars worth of tools in many cases.

After you two TOUCH the freon line with your SOFT HANDS, can you tell us the temperature.

How do you guys check the humidity ? Lick your thumbs and stick it in the air.

What a professional techs we are ? :censored:

I am sorry. But It just is not fit me well to read this stuff in the PROFESSIONAL forum.

Tool-Slinger
09-27-2011, 09:36 PM
After you two TOUCH the freon line with your SOFT HANDS, can you tell us the temperature.

How do you guys check the humidity ? Lick your thumbs and stick it in the air.

What a professional techs we are ? :censored:

I am sorry. But It just is not fit me well to read this stuff in the PROFESSIONAL forum.
On small systems there is often not even any place to put gauges until you break into the system with a tap.

I usually know problems without gauges or thermometers. Bad valves, condenser not doing it's job, evaporator not transferring heat, low on freon, many things. Eyes, ears, hands, and experience.

Example: Suppose refrigerator is not cooling well. If Liquid line is burn your finger hot you probably have a dirty condenser or fan motor problem if there is one. If not, and running, unplug it and listen to the bad valves whistle past to equalize pressure while the compressor shell gets hot to touch.

Not to discourage proper test instruments, not at all. FWIW I can probably get you a line temp within about 5* by hand.

Stephen260B
09-28-2011, 09:03 PM
Hands, ears and eyes are definitely the best tool to use as you begin to asses the system. Checking coils for obstruction, looking at fan motors, sight glass, suction line for moisture ant etc... After doing that if nothing is begging for further examination you should bring out your temp probes, meter and gauges to examine things more closely. As far as pulling the charge on a blended system and recharging....only if it is a small system or the pressures are completely incoherent on a larger system. Its hard to charge the customer for that, especially when its not the main problem. But those are just my thoughts.

HuNGRYTeCH
09-29-2011, 10:49 PM
I will look and feel around the whole system before I pull out my tools. A lot of people get tunnel vision and only fix one part of the problem. I have different procedures for equiptment I maintain and equiptment that is only service when there are problems. I also put my gauges on early in my diagnostics, after taking air tempartures across the evap and cond. You can tell a lot by feeling and seeing but how do you know if you have 10 degree superheat or 50 degrees superheat. Your gauges are your eyes into the system and are the most valuable tool when diagnosing a refrigeration system.

just opinion, I respect you on this forum, but as a "professional" we should not being referring to refrigerant as "freon", I am sure you are aware that it is only a Dupont trademark name and does not accurately describe refrigerants as a whole.

ahiggins91
09-30-2011, 12:38 AM
Suction line should be 'beer can cold', if not, you have a problem.

HuNGRYTeCH
09-30-2011, 10:06 PM
Suction line should be 'beer can cold', if not, you have a problem.

Yeah, you can just cut out some Coors Light mountains and if they turn blue you are good :cheers:

monkeyspanners
10-01-2011, 01:49 PM
Yeah, you can just cut out some Coors Light mountains and if they turn blue you are good :cheers:

Or if you are in the UK look out for some Carlsberg cans as they have a little lock symbol that turns blue when cold enough :whistle:

Trouble is once i've drunk the beer so i can cut the correct charge indicator out of the can i don't care if the system works ok or not...

Hardwater
10-01-2011, 06:13 PM
Here is some information that you might need someday since you don't need instruments in case you get electrocuted but it would be a good ideal to have another tech with you so the two of you can help each other out if need be. There is also a procedure for doing electrical checks without a meter.

Electric Handbook 1942
What do you think of this??

The following is from The American Electricians Handbook (1942) A Reference Book for Practical Electrical Workers. Terrell Croft, consulting engineer. McGraw Hill Book Company, Inc, New York and London 1942


Electricians often test circuits for the presence of voltage touching the conductors with the fingers. This method is safe where the voltage does not exceed 250 and is often very convenient for locating a blown-out fuse or for ascertaining whether or not a circuit is alive. Some men can endure the electric shock that results without discomfort whereas others cannot. Therefore, the method is not feasible in some cases. Which are the outside wires and which is the neutral wire of a 115/230 volt three wire system can be determined in this way by noting the intensity of the shock that results by touching different pairs of wires with the fingers. Use the method with caution and be certain that the voltage of the circuit does not exceed 250 before touching the conductors. (This and the several paragraphs that follow are taken from ďElectrical Engineering


159. The presence of low voltages can be determined by testing. The method is feasible only where the pressure is but a few volts and hence is used only in bell and signal work. Where the voltage is very low, the bared ends of the conductors constituting the 2 sides of the circuit are held a short distance apart on the tongue. If voltage is present a peculiar mildly burning sensation result, which will never be forgotten after one has experienced it. The taste is due to the electrolytic decomposition of the liquids on the tongue which produces a salt having a taste. With voltages of 4 or 5 volts, due to as many cells of a battery, it is best to test for the presence of voltage by holding one of the bared conductors in the hand an touching the other to the tongue. Where a terminal of the battery is grounded, often a taste can be detected by standing on moist ground and touching a conductor from the other battery terminal to the tongue. Care should be exercised to prevent the 2 conductor ends from touching each other at the tongue, for it they do a spark can result that may burn.


RESUSCITATION FROM ELECTRIC SHOCK By Frederick Koliz, MD

1st. Lay the patient on his back, 2 Move the tongue back and forth in the mouth by seizing it with a handkerchief or the fingers, while working the arms to induce respiration. 3. Donít pour anything down the patientís throat. 4. Try to cause the patient to gasp by inserting the first and second fingers in the rectum, and pressing them suddenly and forcibly toward the back. 5. If possible, procure oxygen gas, and try to get it into the lungs during the effots at artificial respiration.:whistle:

Hardwater
10-02-2011, 10:55 AM
At one time where I work there was a supervisor that said he could determine if the compressor is bad or not by "looking at it".

Tool-Slinger
10-02-2011, 11:17 AM
At one time where I work there was a supervisor that said he could determine if the compressor is bad or not by "looking at it".
Obviously he had some of those "X-RAY Glasses" ordered out of the comic book.

Hardwater
10-02-2011, 11:46 AM
Obviously he had some of those "X-RAY Glasses" ordered out of the comic book.

Yeah, I think he was out of a comic book.:LOL:

bunny
10-02-2011, 11:49 AM
Professionals that we are, how would any of us feel going to the doctor and being given a serious diagnosis after feeling our forhead was the basis of the good doctor's diagnosis?

While touching suction and liquid lines, compressor heads, etc can be good indicators of potential problems, there is no substitute for accurage measurement of pressure and temperature.

Tool-Slinger
10-02-2011, 01:19 PM
Professionals that we are, how would any of us feel going to the doctor and being given a serious diagnosis after feeling our forhead was the basis of the good doctor's diagnosis?

While touching suction and liquid lines, compressor heads, etc can be good indicators of potential problems, there is no substitute for accurage measurement of pressure and temperature.
I don't think anyone claimed accurate measurements were not better. Sometimes it is not needed. Sometimes it is a slow way of finding a problem.

Going straight in and attaching all of the gizmos to a unit is kinda simplistic. I do that too, when needed, but I usually can find a problem without all that before I can even attach all of the gizmos. And if I attach gizmos anyway, I already have a better idea what I am looking for. Usually. Most service call situations. It is more a matter of speed. I do not need an hour to attach into a domestic refrigerator and take readings to tell you it has bad compressor valves. Two minutes tops. Usually.

bunny
10-02-2011, 02:43 PM
Slinger, if that method works for you...all the more power to you.

I would say that it's not to methodology which most techs employ.

Tool-Slinger
10-02-2011, 03:28 PM
Slinger, if that method works for you...all the more power to you.

I would say that it's not to methodology which most techs employ.
It may depend on what you are working on. Friday I as doing a PM on a 60 ton unit, I had everything hooked up, it was just a PM job and there were no problems.

Service calls require quick action. It is pretty easy to butt up to replacement costs in a repair situation. We have to go fast, whenever we can. I can spend a half day diagnosing a 30 ton unit with no problem, cannot do that on a little make-table. Labor rates are just too high. We have to be quicker. Generally speaking, one should know what the problem is and options are within half an hour usually. I have no problem with taking detailed measurements, I never said that I did, But in many cases that is just dicking around uselessly for information about the system that we do not need. Bad pump valves, dirty condenser, that sort of thing and there is only a waste of time and customer money trying to diagnose based on accurate readings. Get the big picture.

Hardwater
10-02-2011, 04:44 PM
PM is a whole different ball game. Company's are beginning to tire of some quick in, quick out because their starting to look at it as a half-ass job. This sometimes ends up in a call back and costing them more money and some are beginning to frown on this. The contractors are the ones that are more into the quick approach because it means more money in their pocket not your's.

It isn't any different then doctor's trying to cram as many patient's as they can into 8 hrs of work. They don't spend enough time with the patient to know what's really going on with a persons health.

I had this problem with a contractor and told them to never come back that their services wasn't wanted. So the contract never got renewed and they ended up being the loser over the fast approach. And of course all the instrument's aren't required every single time this is only common sense.

Tool-Slinger
10-02-2011, 04:59 PM
PM is a whole different ball game. Company's are beginning to tire of some quick in, quick out because their starting to look at it as a half-ass job. This sometimes ends up in a call back and costing them more money and some are beginning to frown on this. The contractors are the ones that are more into the quick approach because it means more money in their pocket not your's.

It isn't any different then doctor's trying to cram as many patient's as they can into 8 hrs of work. They don't spend enough time with the patient to know what's really going on with a persons health.

I had this problem with a contractor and told them to never come back that their services wasn't wanted. So the contract never got renewed and they ended up being the loser over the fast approach. And of course all the instrument's aren't required every single time this is only common sense.
My apologies. This is my own PM on my own time and dime. I was just trying to make the point in differences of equipment. Some things afford more attention.

I just start with hands/ears/eyes first on a service call. That is not a proper diagnosis, just the fast way to lead to the problem usually. I may not need gauges, I may not need a meter, I may not need a thermal probe, but of course I have them in my toolbag. I respect your respect for proper procedures I guess.

Hardwater
10-02-2011, 06:25 PM
My apologies. This is my own PM on my own time and dime. I was just trying to make the point in differences of equipment. Some things afford more attention.

I just start with hands/ears/eyes first on a service call. That is not a proper diagnosis, just the fast way to lead to the problem usually. I may not need gauges, I may not need a meter, I may not need a thermal probe, but of course I have them in my toolbag. I respect your respect for proper procedures I guess.

I wasn't pointing the finger at you and I hope you didn't take it that way and if you did I apologize to you. I was saying it's what's becoming popular. I don't use instrument's every single time. A good tech knows when he needs to analyze things further.:cool:

bunny
10-02-2011, 06:42 PM
Generally speaking, one should know what the problem is and options are within half an hour usually. I have no problem with taking detailed measurements, I never said that I did, But in many cases that is just dicking around uselessly for information about the system that we do not need. Bad pump valves, dirty condenser, that sort of thing and there is only a waste of time and customer money trying to diagnose based on accurate readings. Get the big picture.

I once changed a scrambled Carrier 06E compressor on a supermarket multiplex rack. All of the normal procedures were followed pertaining to diagnostics, however no problem could be found. A repeat failure happened a week later on a different compressor. At this point another tech was called in to assist with the diagnosis...still no fault was found.

It wasn't until a few weeks later that we stumbled upon the problem. The previous contractor....likely a get in and get out contractor....replaced an alleged underground leaking line with a new overhead line. They made one crucial mistake....they forgot to add a trap to the suction riser.

The entire case lineup became the trap, and when it had logged enough oil resultant to an excessive pressure drop in the suction side of the system, it would force a slug of oil back to the rack.

We probably should have been good enough to diagnosis this within half an hour, but....

The point is: It's a little dangerous, and perhaps even a little arrogant to issue blanket statements such as this. Also, to assume one can diagnose the problem without the proper data (pressure, temperature, etc) could lead to a tunnel visioned diagnostic procedure, fueled by arrogance, that could increase time on the job, cost the customer money, etc.

Certainly on a small piece of equipment with a scorching liquid line, it's pretty easy to look at the condenser and see if it's plugged up. Cleaning it is a quick remedy. Yet it's still good practice to attach the "gizmos", and see if the compressor suffered any ill effect due to the high discharge pressure/temperature condition brought about by the dirty condenser.

Tool-Slinger
10-03-2011, 03:04 AM
I once changed a scrambled Carrier 06E compressor on a supermarket multiplex rack. All of the normal procedures were followed pertaining to diagnostics, however no problem could be found. A repeat failure happened a week later on a different compressor. At this point another tech was called in to assist with the diagnosis...still no fault was found.

It wasn't until a few weeks later that we stumbled upon the problem. The previous contractor....likely a get in and get out contractor....replaced an alleged underground leaking line with a new overhead line. They made one crucial mistake....they forgot to add a trap to the suction riser.

The entire case lineup became the trap, and when it had logged enough oil resultant to an excessive pressure drop in the suction side of the system, it would force a slug of oil back to the rack.

We probably should have been good enough to diagnosis this within half an hour, but....

The point is: It's a little dangerous, and perhaps even a little arrogant to issue blanket statements such as this. Also, to assume one can diagnose the problem without the proper data (pressure, temperature, etc) could lead to a tunnel visioned diagnostic procedure, fueled by arrogance, that could increase time on the job, cost the customer money, etc.

Certainly on a small piece of equipment with a scorching liquid line, it's pretty easy to look at the condenser and see if it's plugged up. Cleaning it is a quick remedy. Yet it's still good practice to attach the "gizmos", and see if the compressor suffered any ill effect due to the high discharge pressure/temperature condition brought about by the dirty condenser.
I think we agree. I use hands/eyes/ears for speed. But some jobs require baby-sitting, and any are better served by the best tools applied. Refrigeration is more demanding I understand.

In the real world of demanding employers and customers, any help in making a fast diagnosis is great. When possible. I love my tools and gizmos but sometimes do not need them.

WestcoastApprentice
03-18-2012, 01:40 PM
Unless it is a critically charged system, I'm hooking up gauges very early in the troubleshooting process.

Once the compressor is running, I want pressures.

Seriously guys, this post simplifies it. "looking" at compressors or "grabbing" lines with hands to get a feel of what the #$%^ is going on in the system??? the only guy who I've ever met in the trade who used these practices was a tech from Grand Cayman Island that didn't own a vacuum pump or Nitrogen regular because R22 was cheap enough there to just purge the #$%^ out of the system before start up......Try going into a wholesalers once in the last 5 years and take a look at some of the diagnostic tools that are out there; this aint the wild west of re-frig-er-ation any more boys!

timebuilder
03-18-2012, 03:43 PM
Once in a while I get a refridge system that is large enough for service valves. Usually, it's a reach-in with no valves.

Condenser dirty? I've had sweaters on some.

Defrost timer used? Is it working? Set to roughly the correct time? Stuck in a defrost period?

Compressor runs? Fans run?

Time for the piercing valve. Pressures and temps.

This gets me to a point where I can do pinpoint testing, if needed.

Top failure is blocked cap tube.

Second is bad fans.

Third is defrost timer.

Fourth is lost charge, usually in the back wall where piping cannot be accessed. New unit.

Fifth is bad compressor.

jburchstead
03-18-2012, 10:10 PM
Here is some information that you might need someday since you don't need instruments in case you get electrocuted but it would be a good ideal to have another tech with you so the two of you can help each other out if need be. There is also a procedure for doing electrical checks without a meter.

Electric Handbook 1942
What do you think of this??

The following is from The American Electricians Handbook (1942) A Reference Book for Practical Electrical Workers. Terrell Croft, consulting engineer. McGraw Hill Book Company, Inc, New York and London 1942


Electricians often test circuits for the presence of voltage touching the conductors with the fingers. This method is safe where the voltage does not exceed 250 and is often very convenient for locating a blown-out fuse or for ascertaining whether or not a circuit is alive. Some men can endure the electric shock that results without discomfort whereas others cannot. Therefore, the method is not feasible in some cases. Which are the outside wires and which is the neutral wire of a 115/230 volt three wire system can be determined in this way by noting the intensity of the shock that results by touching different pairs of wires with the fingers. Use the method with caution and be certain that the voltage of the circuit does not exceed 250 before touching the conductors. (This and the several paragraphs that follow are taken from ďElectrical Engineering


159. The presence of low voltages can be determined by testing. The method is feasible only where the pressure is but a few volts and hence is used only in bell and signal work. Where the voltage is very low, the bared ends of the conductors constituting the 2 sides of the circuit are held a short distance apart on the tongue. If voltage is present a peculiar mildly burning sensation result, which will never be forgotten after one has experienced it. The taste is due to the electrolytic decomposition of the liquids on the tongue which produces a salt having a taste. With voltages of 4 or 5 volts, due to as many cells of a battery, it is best to test for the presence of voltage by holding one of the bared conductors in the hand an touching the other to the tongue. Where a terminal of the battery is grounded, often a taste can be detected by standing on moist ground and touching a conductor from the other battery terminal to the tongue. Care should be exercised to prevent the 2 conductor ends from touching each other at the tongue, for it they do a spark can result that may burn.


RESUSCITATION FROM ELECTRIC SHOCK By Frederick Koliz, MD

1st. Lay the patient on his back, 2 Move the tongue back and forth in the mouth by seizing it with a handkerchief or the fingers, while working the arms to induce respiration. 3. Donít pour anything down the patientís throat. 4. Try to cause the patient to gasp by inserting the first and second fingers in the rectum, and pressing them suddenly and forcibly toward the back. 5. If possible, procure oxygen gas, and try to get it into the lungs during the effots at artificial respiration.:whistle:

Thanks for taking the time to post this, this is funny stuff. Actually I am old enough that some of the low voltage stuff was taught to me and practiced. The high voltage was all inadvertant and went well beyond the recommended voltage>

derekkite
04-18-2012, 02:15 AM
What do I do? I look in the cooled space. Are the fans working, are they hot? Is the coil plugged? Is it iced up? Then look at the condensing unit. Is it plugged? Fans running, hot? Is the compressor too hot? Listen for noises. 3/4 of the time you found the problem already, then it is a matter of fixing what you found.

If that isn't enough, or once everything else is in order, get out the guages. Check the refrigerant charge, find and fix leaks. Is the compressor pumping to capacity? Is the metering device metering? What is the defrost strategy? Is there a clock, does it work?

If not, then off cycle and the system is capacity critical. Why is there not enough capacity? Check usage pattern, a ton of warm fruit will cause problems in an otherwise perfectly working system. Understanding the design parameters of sizing helps here.

That will get you to 95% of the problems. The other are intermittant oddities. Or out of the ordinary like pickled systems or non condensibles, or mismatched components, or just plain bad design that would never work and you are the 6th that have looked at it and you won't be able to do anything miraculous either.

The majority are components failed or no airflow due to filth. Pretty easy to find.

I didn't mention thermostat because that one usually thumps you on the head right away. If nothing is running and you don't check the thermostat it may be time to try something else.

And I wouldn't diss those who feel their way. What is the error of your thermometer compared to superheat? It is common for digital thermometers at low temperatures to have an error wider than the superheat you are trying to set. A mechanic who doesn't know how a low temp superheat feels on the back of his hand will miss quite a bit. Or how a medium temp walkin should feel like if humidity and temperature are correct. Many times my instruments told me that it was working but it wasn't.