Troubleshooting table

[nike123]

Quick troubleshooting tips for A/C's

[The Viking]

Nice one.

Thank you for sharing.

[dsp]

Awesome info!!

[Gary]

Quick troubleshooting tips for A/C's

Hmmm...

Head pressure is not a valid symptom. On a cool day we would expect the head pressure to be lower and on a hot day we would expect the head pressure to be higher. So we must consider both and they should both be in the form of temperature.

We convert the head pressure to temperature on our P/T chart. This is our saturated condensing temperature (SCT). We subtract the temperature of the air entering the condenser (ambient) from the SCT and this gives us the condenser TD. Condenser TD would be a valid symptom.

Similarly, suction pressure is not a valid symptom, because we must also consider the temperature of the air entering the evaporator coil. With warmer entering air we would expect the suction pressure to be higher and with cooler entering air we would expect the suction pressure to be lower.

We convert the suction pressure to saturated suction temperature (SST) on our P/T chart and subtract this from our entering air temperature, which gives us our evaporator TD. Evaporator TD is a valid symptom.

Pressures don't tell us anything until we convert them to saturation temperatures and saturation temperatures don't tell us anything until we compare them to other temperatures.

Back in the good old days when there were three main refrigerants (R12, R22 and R502) I used to tell people to black out the pressure scales on their gauges with a magic marker and directly read the saturation temperatures. Thinking in terms of saturation temperatures instead of pressures makes trouble shooting a lot easier. Nowadays with all of the different refrigerants you need a P/T chart.

[Gary]

Quick troubleshooting tips for A/C's

Discharge temperature pretty much tracks compressor inlet superheat, except when the compressor is inefficient. When the compressor is inefficient there is extra heat added to the discharge.

At one one point I invested an enormous amount of research into devising a chart to compare discharge temperature to compressor inlet superheat in order to identify inefficient compressors.

It turned out to be far too complex and specific to the compressor in question, so I was not able to devise a chart that was reliable enough.

[nike123]

Hi Gary!
Is this table then OK, or we need to change some directions of arrows?

[paul_h]

Charts like those have been around for a long time, and I think they are handy when learning the concepts of refrigeration. Most panasonic service manuals even include something similar, so I've seen them all the time.
While they are a good guide, you can't fit every senario or experience into a chart.
I don't believe pressure is useless either, unit's cut out on HP or LP faults all the time. Could be an installation fault, dirty coils or filters or faulty sensor. I don't live in a perfect engineering world, but in the dirty alleys, stuff happens and you need to check pressures.
edit: temps are the language I speak to other mechanics in, if I can't fix then my reports are in temps. But in initial diagnostics I consider pressures, eg HP trips, gas leaks etc if that's the complaint.

I also believe that knowing what to look for, knowing plant history, and knowing where to go for first measurements is most important.
Eg, most small splits and refrigeration I've worked on do not have a head pressure access point, suction only. Most commercial stuff if it's old and has a good service history, normally has something obvious wrong with it, like broken controller or fan.
That's most of my life right there, useless small stuff and good old obvious stuff.
The chart is handy so maybe people can get something off it.
But it would never replace an experienced mechanic.
Not that I'm saying that's what you were doing, I'm just saying that mechancs will always say there's exceptions and the chart isn't good enough
When an apprentice starts out, give him a chart similar to that, hopefully it will help them. Buy the time they complete their apprenticeship, hopefully such a chart should not be needed by them

[Gary]

I agree with paul h that such charts have limited value, however...

If I were devising a chart it would look entirely different from this one, but let's see if we can improve it a little:

Sequence is important. I would start by rearranging the left hand side. It should be:

Low evap
air flow

Low cond
air flow

Overcharge

Restriction
(high side)

Undercharge

TXV
overfeed

Inefficient
compressor

There are lots of other changes I would make, but that's a good start.

[Gary]

You'll note that I have changed a couple of the labels. A restriction isn't necessarily the drier. It could be anywhere in the liquid line up to and including a restricted TXV inlet strainer... or it could be that the guy before you "adjusted" the TXV. In a perfect world, the commissioning tech would adjust the valve and then superglue the stem.

I also changed "Loose TXV bulb" to "TXV overfeed" to include misguided techs screwing up the adjustment.

[nike123]

. In a perfect world, the commissioning tech would adjust the valve and then superglue the stem.

It could be done with postal sealing!

[nike123]

I agree with paul h that such charts have limited value, however...

If I were devising a chart it would look entirely different from this one, but let's see if we can improve it a little:

Sequence is important. I would start by rearranging the left hand side. It should be:

Low evap
air flow

Low cond
air flow

Overcharge

Restriction
(high side)

Undercharge

TXV
overfeed

Inefficient
compressor

There are lots of other changes I would make, but that's a good start.

Than this is new one!


I also uploaded word document so anyone can contribute own ideas:
Identify Trends in Refrigeration systems3.doc

[Gary]

Notice that the two charts are almost identical. The only thing that is added for a TXV system is overfeed.

[nike123]

Charts like those have been around for a long time, and I think they are handy when learning the concepts of refrigeration. Most panasonic service manuals even include something similar, so I've seen them all the time.
While they are a good guide, you can't fit every senario or experience into a chart.
I don't believe pressure is useless either, unit's cut out on HP or LP faults all the time. Could be an installation fault, dirty coils or filters or faulty sensor. I don't live in a perfect engineering world, but in the dirty alleys, stuff happens and you need to check pressures.
edit: temps are the language I speak to other mechanics in, if I can't fix then my reports are in temps. But in initial diagnostics I consider pressures, eg HP trips, gas leaks etc if that's the complaint.

I also believe that knowing what to look for, knowing plant history, and knowing where to go for first measurements is most important.
Eg, most small splits and refrigeration I've worked on do not have a head pressure access point, suction only. Most commercial stuff if it's old and has a good service history, normally has something obvious wrong with it, like broken controller or fan.
That's most of my life right there, useless small stuff and good old obvious stuff.
The chart is handy so maybe people can get something off it.
But it would never replace an experienced mechanic.
Not that I'm saying that's what you were doing, I'm just saying that mechancs will always say there's exceptions and the chart isn't good enough
When an apprentice starts out, give him a chart similar to that, hopefully it will help them. Buy the time they complete their apprenticeship, hopefully such a chart should not be needed by them

I totally agree with you Paul, just wanted to play a little. Maybe, with playing, we make slightly better one than those in existence around.

[Gary]

Hmmm... I would add a couple more columns labeled "Evap dT" and Cond dT". The columns would then be rearranged: Evap delta-T, Cond delta-T, Subcooling, Superheat, Evap TD, Cond TD, Comp amps, Discharge temp.

[Gary]

For those of you who may not be aware, the delta-T aka dT is the coil entering air and leaving air temperature difference. It is an indicator of air flow problems.

[Gary]

Here's my version of the [limited value] trouble shooting chart:

[nike123]

Here's my version of the [limited value] trouble shooting chart:

What you mean by "limited value"?
What is with empty fields?

[nike123]

I have one slide rule on Croatian language but I think his origin is from big names as Carrier or York.

Does anybody see this before on English?

It is 10 years in my tool bag and I think that engineer who gave it to me has got him also 10 years.
This is picture of both sides of rule:

[Gary]

What you mean by "limited value"?

As we discussed earlier, all such charts have limited value. There are exceptions and variations to everything. The devil is in the details.

What is with empty fields?

The empty fields are irrelevant, ambiguous or insignificant.

When trouble shooting a system, start at the top of the table and work your way down.

Every service call should start with a visual inspection of the system. In particular, you are looking for airflow problems.

The delta-T's are for confirmation. If you have a high delta-T, you have an airflow problem, regardless of what your visual inspection tells you and regardless of anything else in that table.

Now continue working your way down the list.

First things first and second things second. I'm a sequential kind guy.

[nike123]

First things first and second things second. I'm a sequential kind guy.

That is pretty much my method, even so, I sometimes go first for known problems of model I am working at, and if that doesn't produce quick result, then I go to methodical troubleshoot.
It could be time saver, and sometimes time waister.

[Gary]

That is pretty much my method, even so, I sometimes go first for known problems of model I am working at, and if that doesn't produce quick result, then I go to methodical troubleshoot.
It could be time saver, and sometimes time waister.

There is an ongoing struggle in our trade between doing it fast and doing it right. Refrigeration is a business and in order to best serve our customers and make a reasonable profit, shortcuts are often prudent. And the truth be known, in most cases the fast way works.

What I find truly disturbing is that most service techs don't know how to do it the right way. Worse yet, they believe the fast way IS the right way. Bad enough that they don't know, but worse, they don't know that they don't know.

[nike123]

There is an ongoing struggle in our trade between doing it fast and doing it right. Refrigeration is a business and in order to best serve our customers and make a reasonable profit, shortcuts are often prudent. And the truth be known, in most cases the fast way works.

What I find truly disturbing is that most service techs don't know how to do it the right way. Worse yet, they believe the fast way IS the right way. Bad enough that they don't know, but worse, they don't know that they don't know.

We have one adage with meaning something like this (this is translation and I dont know if it sound meaningless on English):
What increasingly I know, that increasingly I know how litlle I know.

[jahangir.ahmad]

Hi
Iam Asst Engineer In Haier Pakistan Ltd The Worlds Largest Home Applaince Company
I Want To Question ?
Like How We Designe The Evaporator In Freezer ?
Whats The Factors Required To Design The Evaporator ??
Im Waiting For Your Reply

Jahangir Ahmad Khan

[nike123]

Hi
Iam Asst Engineer In Haier Pakistan Ltd The Worlds Largest Home Applaince Company
I Want To Question ?
Like How We Designe The Evaporator In Freezer ?
Whats The Factors Required To Design The Evaporator ??
Im Waiting For Your Reply

Jahangir Ahmad Khan

You should try Google for your hunting.

From your questions, I am little worried for future of that Worlds Largest Home Appliance Company if you are some kind of refrigeration Engineer.

I don't understand how somebody could have assignment to make calculations of home appliance as job and be payed for that, and in the same time asking on internet that someone guide him or make calculations for him. If you are assistant engineer then you should be asking questions and guidance that engineer whom you assist.

Here is some useful links for you:
http://tinyurl.com/2fo8km
http://www.embraco.com/ingles/informacoes_tecnicas.htm

[Ozfridgie]

Very wise, I always tell my apprentices to cary PT chart.

[Buckiesr]

You should try Google for your hunting.

From your questions, I am little worried for future of that Worlds Largest Home Appliance Company if you are some kind of refrigeration Engineer.

I don't understand how somebody could have assignment to make calculations of home appliance as job and be payed for that, and in the same time asking on internet that someone guide him or make calculations for him. If you are assistant engineer then you should be asking questions and guidance that engineer whom you assist.

Here is some useful links for you:
http://tinyurl.com/2fo8km
http://www.embraco.com/ingles/informacoes_tecnicas.htm

that was a pretty rough reply to the Engineers question. On the contrary to your rebuke, A smart Engineer knows how tunnel vision effects any industry and the ability to think outside of the box is not a gift everyone receives. Inquiring concerning design ideas from the people who work with the end product, is a good insightful resource. I worked for a fortune 500 company at one time that employed the brightest engineers I have ever worked with. They always encouraged us to carry writing material in the field to note modifications, suggestions and ideas we discovered the end user to have in use or suggestions for improving the products we designed, produced, sold, and serviced because as gifted and educated as they were, they knew the end user would always solve the issues and limitations they faced. I think our Pakistani RE partner is on the right tract to innovating the best freezer coil design in the world, and gather the best information from the most informed frontline, end user sources. That is a very smart Engineer indeed. Google indeed!
Buckiesr