Over-heating compressors !

[wallerboy76]

Hello fellow Engineers & Technicians,

I will really like to see if you guys can help me in a simplified manner :confused: I have been replacing compressors on domestic fridges( this happens on any unit:- ac's, walk in freezer, chiller any size, etc etc )... they have been overheating & breaking on overload, I have been following all the necessary precautions...I know that I have not giving the necessary info.

But what I'm really asking is: what are the possible reasons why a-any compressor would over-heat ?

Whoever really knows can you please help me answer this question ?(the wise guys who try to insult/boost their ego dont have 2answer this) Can you give me a list of possble reasons?

Thanks in advance

Wallerboy76

[sedgy]

hi wallerboy 76, on domestics the gas charge is very important it is very easly over charged , do you vac out and messure the gas in weight?

[Gary]

Hello fellow Engineers & Technicians,

I will really like to see if you guys can help me in a simplified manner :confused: I have been replacing compressors on domestic fridges( this happens on any unit:- ac's, walk in freezer, chiller any size, etc etc )... they have been overheating & breaking on overload...

How do you know that they are "overheating & breaking on overload"?

[lowcool]

the only common denominator i see is a faulty vacumm pump,have you experienced high head pressures?

[R. skiffington]

If it is Over heating. On domestics, most likely causes would be damaged comp valves, blocked capillary, shortage of refrigerant. If system has been opened you could have non-condensables. Remember that a comp overload or klixon is operated by heat, this can be actual heat from comp body or current.

[nike123]

I have been replacing compressors on domestic fridges( this happens on any unit:- ac's, walk in freezer, chiller any size, etc etc )... they have been overheating & breaking on overload, I have been following all the necessary precautions...I know that I have not giving the necessary info.



Are you saying that you are replacing compressors AGAIN after you first replaced original compressor, and that REPLACED compressor has worked some time?

If yes, describe in detail your replacement procedure and selection method of replacement compressor.

[wallerboy76]

Hi,
Thanks again for the appreciated response.
'Sedgy' I did vacuum the system appox. 20mins, if the pump is working efficiently thats another matter.
I will look into that 2day. Maybe its not & non condensables remained in it(thank u lowcol/skiffington) but I would really like to know what is the difference between psi & psig if there is one? How & with what u measure the gas in weight? yes there is high head pressure!

wallerboy76

[Yuri B.]

what is the difference between psi & psig if there is one? How & with what u measure the gas in weight?
"Gas charge" is sort of professional slang - for refrigerant charge. A value in psi a(bsolute) has the starting point from absolute vacuum, a value in psi g(auges) has start point from the atmospheric presure.

[jcook1982]

"Gas charge" is sort of professional slang - for refrigerant charge. A value in psi a(bsolute) has the starting point from absolute vacuum, a value in psi g(auges) has start point from the atmospheric presure.

Atmospheric pressure is 14.7 psi or 101.3 kPa . In USA our gauges normally come in measuring PSIG so there is no need to add the 14.7 to the psi reading. I am not sure if gauges in Europe start at atmospheric.

If you are having high head pressure you may have non-condensables.. what kind of suction pressures are you seeing?

[lowcool]

the thing that has got me stuffed is that its over a variety of systems,my initial thought was crook refrigerant until i saw low med and high temp systems,unless their all on 22.if your replacing units with a generic brand instead of original you may have different compressor capacities.

[Gary]

the thing that has got me stuffed is that its over a variety of systems...

We know that these compressors are "overheating & breaking on overload" because someone who doesn't know what psi means is telling us that it is so.

He hasn't told us the symptoms which lead to this conclusion.

[mad fridgie]

I to am a little confused (not hard) is he talking in general terms or just after retrofit.
In general terms if a compressor has been running lets say in excess of 10years, is not just easy to say that it has come to the end of its life. After years of running parts are worn, efficiency is down, this tends to lead to high drawn power, thus a hot compressor. (put down the old dog)
If this is happening after retrofit, then obvoiusly some problem with install/commissioning method.
Fly me over to barbados, and I will give a bit of training for free.

[desA]

If on new systems in Barbados, then the question needs to be asked:

What is your power quality like?

[lowcool]

i gave the benefit of doubt

des ,get back in the wind

[wallerboy76]

Hi again,

First let me say I'll try 2address all the credible comments & gary with this post...I did not answer u bcuz i choose not 2...it doesnt help my situation...I kno what the technical term in the books for psi & psig is but i was wonderin what or if these terms referred to the pressure when the compressor is off/runnin...for instance e.g the unit manu. design pressure reads lowside 140 psig(kpa 965) & highside 320 psig(kpa 2206) but its a small deep freeze desktop lowtemp...we kno u shud check the pressures when the cabinet area is about 26.7c (temps drop=pressure drops) thats what i was hoping 2get from u guys...see my problem/my confusion.

I was not sayin 'lowcool' i changed comp. on all these different temps at present but that comp. of all temps overheat & i wanted a list of all the possible reasons why this would happen... in barbados we never have the same generic brand & yes i honestly believe the comps they bring is different in cubic capacity.

'gary' hmm where should i start... the system only operates on a thermostat, no timer, no condenser fan, the coils are in the body of the unit... beside the overly high current draw/heat of comp. Reasons for saying its breaking on overload: the comp. is shotting off/pressure level on gauges rises/highside copper pipes getting cooler, etc,etc. while the cabinet door is opened wide, stays off 30-40,mins !

Its not a retrofit but a changed of compressor in one instance. same gas & yes, in barbados has the worst power supply quality you would ever come accross(volts in 1building u can get between 97-146 volts, dedicated 50hz) but normally after a transformer this is no real problem!

thanks boyz hope this helps

wallerboy76

[Gary]

If you went on a service call and the customer told you the system needed refrigerant, would you add refrigerant or would you check the system temperatures and pressures to see if that was the problem?

If you want help, give us a full description of the system along with all of the temperatures and pressures. We can't help you if all you give us is your opinions and conclusions.

We can't see the system from here and we can't read your mind.

[oldesky]

Hi Wallerboy, I will try to answer your question without taking you around the merry go round. Hermetic compressors overheat due to high discharge temperatures. Most hermetic compressors are suction cooled and therefore rely on the returning low pressure refrigerant to cool the motor. Domestic compressors generally work at low back pressure so therefore the return refrigerant to the compressor has a low vapour density.If the return vapour temperature is too high when it returns to the compressor the motor runs hotter and the vapour temp entering the compressor is even higher. This extra "heat" must be rejectected by the condenser in the form of a higher discharge temperature. Your system can be operating around the correct condensing temperature but with an excessive compressor discharge temperature. Ths can cause the oil to carbonise and "coke" the valve reeds thereby causing lack of compression. As the temperature rises chemical reaction increases and may cause acid formation and eventual motor burn out. Some refrigerants are worse than others especially at low temperature such as R22. I suggest you look at or get someone to show you a Molier Chart in the superheated vapour area and you will be able to see the effects of high suction return temperatures. The best way to limit this problem is to keep the return suction temperature at the compressor down to a reasonable limit. I use as my rule of thumb 20K max on medium temp and 15K max on low temp. Others will have their own idea but this has worked for me. Others will tell you many other reasons but I believe this to be the main cause especially on an otherwise well balanced system.There are ways and means of combatting this problem but I have stuck to your original question and hopefully answered it.

[wallerboy76]

But what I'm really asking is: what are the possible reasons why a-any compressor would over-heat ?

Gary I'm sorry if this is difficult 4u 2understand it was never meant 2be...I may have phrased my question wrong but AGAIN what I'm really askin is not for u2 help me trouble-shoot this particular problem but rather 2things;-

1-ALL the possible reasons why a/any compressor would overheat that maybe experienced & not found in a book that u guys may have come accross &

2- why the reading on the gauges never seem 2match the designed manu. labelled reading that the system comes with in terms of pressure.

To be perfectly clear it would be most appreciated if u can tell me if there's a different term of refering to pressure when the unit is running & when the unit is not.

If its a foolish question to u guys, i apologise in advance :-) but it would be of great help to me & maybe someone(s) else that was afraid to ask !

wallerboy76

[wallerboy76]

Hi Oldesky,

That info. was most appreciated & altho this is knowledge that u wud have known & come accross in your studies, one can 4get/overlook, maybe sometimes technically complicating a simply solution as such.

76

[desA]

i gave the benefit of doubt

des ,get back in the wind

Eh? :confused: :eek:

[desA]

in barbados has the worst power supply quality you would ever come accross(volts in 1building u can get between 97-146 volts, dedicated 50hz) but normally after a transformer this is no real problem!


There we go...

If any of these systems are not connected to a transformer, then the compressors will have difficulty on start-up, against low voltage - drawing high amperage, & possibly damaging the compressor. Repeat this hundreds of times & you have a recipe for problems.

People need to have lived in areas of poor power quality to really appreciate the effect of these constant 'brown-outs' on domestic appliances.

[wallerboy76]

A part of nature as a defence mechanism, 'the small try to appear larger/bigger than they are so they wouldn't be eaten by larger/bigger predators.'

Hope that doesn't offen u !

76

[wallerboy76]

This is not directed or address to anyone in specific...but the person that is seeing my quest for knowledge as a short coming or lact of something.

76

[Gary]

My mistake. I thought you wanted to know why you are losing compressors... when all you really wanted to know was why compressors overheat.

[nevgee]

That wasted a lot of time ...?

[nevgee]

'the small try to appear larger/bigger than they are so they wouldn't be eaten by larger/bigger predators.'


What is that all about ....:eek:


If one inflates/ makes bigger / over / exessively/ beyond/ further than/ one's own structural / building/ framework/ limits ....one will fall over .../ collapse or even be found / discovered ...exposed ;)

But then some try to fluff up bigger than the one's fluffing up and they all fall down ..while every one else gets on with their stuff.
hey ho :)

[lowcool]

Eh? :confused: :eek:

gday des
last place of residence was on a boat wasnt it?now im confused jeez i must lead a boring life.
get back out their and suck that fresh air and as many beverage containers as you like
cheers