How to trouble shoot a system

[US Iceman]

Having just read a post by one of the other Moderators of this forum I noticed a common problem occuring, which he also mentioned.

People come onto the RE forums and asking for help is great. This is a good resource for others in our industry to use and exchange views.

The common problem which seems to occur a lot is; someone will ask a question, without providing sufficient information for the moderators or others to fully understand your questions.

In order to fully realize the nature of the problem we usually ask many questions. These almost always are related to the operating conditions of the system.

Attached is basic diagram to illustrate why we ask these questions. The diagram is for a simple refrigeration system. In this diagram you will see four different areas where pressures and temperatures are shown.

These basic points of operation provide the condition of the refrigerant on each side of the component, i.e., compressor, condenser, expansion device, and evaporator.

These data points indicate what the refrigerant is doing at each location and helps to show what may be normal or causing the problem.

This does not take expensive or fancy tools; only a gauge set and a thermometer.

With this information and knowing which refrigerant is being used in the system, you can determine a lot of the problems as you gain experience. One of the benefits of this is; you become more familiar with the state of the refrigerant by knowing the pressure and temperature at each location.

All normally used refrigerants are similar. At some operating condition the refrigerant can be 100% liquid, 100% gas, gas & liquid, or superheated or subcooled.

Only gases can be superheated, and only liquid can be subcooled.

By also having the pressures at each component (in & out) you also develop some experience in reasonable pressure losses between the components.

Try this out and think about it. Ask questions. I think you will find as you get used to doing this, your job gets a little easier and less frustrating.

One last comment for consideration. Some of the best tools for trouble shooting refrigeration systems are:

a) eyes
b) ears
c) touch
d) smell
e) feet

All of the above?

Which ones do you use?

[LRAC]

One last comment for consideration. Some of the best tools for trouble shooting refrigeration systems are:

a) eyes
b) ears
c) touch
d) smell
e) feet

All of the above?

Which ones do you use?

Hi US Iceman

The forum has one basic flaw as you mention knowing the level of competance of the poster. All of the above are used by experienced engineers before any guages are attached to a system.

To many engineers completely miss a correct diagnosis by jumping in feet first without sitting back and thinking the process through on what stage the refrigerent is at or even if its an electrical fault causing problems.

My advice is always do the above visual checks and listen to what the customer is saying about the kits operation.

I have become a bad engineer because i find it hard to stand back and let the trainees diagnose a fault as i get frustrated at the time taken when a visual check could have found the fault more quickly.

But i suppose they will get it with time, the hardest thing to explain to trainees is how refrigerent works, they don't know what stage the refrigerent is at in a system and what its doing. But as you say use all of the above FIRST.

Kind regards
Lrac

[US Iceman]

Hi Lrac,



...the hardest thing to explain to trainees is how refrigerent works, they don't know what stage the refrigerent is at in a system and what its doing.


I believe you are right. The common problem is that people start to look at the pressures first. Then it seems the judgement of what's normal is based off of the previous systems observed.

To me it makes more sense to understand why the pressures are what they are and what contributes to the pressures.

The touching of certain areas to find abnormal conditions is what we do after realizing the importance of the relationship between pressures and temperatures.

It's sort of "the chicken and egg theory". Which one comes first?

[old gas bottle]

i normaly go to site,use my eyes to look if its a pile of poo,listen with my ears to see if anyone is comming,use my feet to run off,touch the car and smell the exaust fumes as i race off home,

bet thats the wrong answer iceman "eh" only joking.

[Peter_1]

US Iceman, 5. Feet:confused: ?
Is that when you're so desperate that you give it a kick like The Fonz in Happy Days, kicking his jukebox? :D

It's such a pitty that you - I mean posters in general - can't understand Dutch. I wrote for the Belgium magazine Cool&Comfort two articles about diagnosing a system with your senses, without even using a gauge or a thermometer.

'Ears' is also listening to the specific noises of the different components but even much more important is listening to what the customers tells you.
Even if your client is a butcher and doesn't know anything about refrigeration, you will find clues in his story to help you solve the problem or to divert your search in a certain direction.
But you have to ask him the right questions.

[US Iceman]

US Iceman, 5. Feet:confused: ?
Is that when you're so desperate that you give it a kick like The Fonz in Happy Days, kicking his jukebox? :D


Feet would have several uses. One of them is what you describe, or, kicking the other serviceman or yourself, or for running away!:D

What you say is important for others to realize. This style of troubleshooting should be the first method used before gauges are attached.

Perhaps another use for the feet would be to walk around the system first, before doing anything. All of the little clues are almost always very visible.:cool:

[US Iceman]

bet thats the wrong answer iceman "eh"...


Well that's not quite what I had in mind. But I knew what you meant!;)

[Peter_1]

I don' think your have to use your feet somewhere in your avatar MrcoolingMagic

[Tycho]

Ask the on site machinist for as much information as possible when you get there, angle the same question differently to see if you can get more information.

when you think you have a slight idea of what might be the problem:

-Start it up.

-Stand back, watch and listen.

Often what you first think is the problem isnt, so dont tell the owner/machinist "oh, that sounds like it's the xxxxxx messing up" cause it might not be :)

also, don't go around tapping all the manometers, if you were supposed to tap them, they would come with a small hammer :) and the level sight glasses only needs a quick look... no reason to stare at them for five minutes :)

[ultralo1]

last comment for consideration. Some of the best tools for trouble shooting refrigeration systems are:

a) eyes
b) ears
c) touch
d) smell
e) feet

All of the above?



That is one reason I enjoy working with ULTs. most dont have access valves. The ones that do, the manufactuer tells not to use them.

The good ULTs hav thermocouples embedded in the heat exchanger. The "inexpensive" ULTs dont have any. So we have to use all senses to trouble shoot what is happening.

[Gary]

Refrigerant pressures and temperatures don't mean a thing if you don't have sufficient airflow through both the evaporator and condenser. A quick visual inspection of the coils/fans makes troubleshooting much easier.

[US Iceman]

Refrigerant pressures and temperatures don't mean a thing if you don't have sufficient airflow through both the evaporator and condenser. A quick visual inspection of the coils/fans makes troubleshooting much easier.


I agree. This is why you should look at the system before getting all excited about the gauges.

Eyes was number 1 on my list!:D

[giovanni]

I agree with eyes,ears,touch,smell,feet theory. Works very well especially the eyes, ears, and touch. I have prevented a few breakdowns with these, such as plastic bags covering the air inlets on glycol pumps, snow or ice covering fins on air cooled units and just knowing the sounds of a system and the feel of certain pipes on the system. Have even gone as far as taking temperature readings with infa red temp gun on certain parts of the unit and logging them for reference.