Odd fuse blow

[nike123]

I have recently called to service chiller for residential cooling and heating which doesn't give sign of life.
After check, I found fuse SF2 (4A) blown. I replaced it and checked current draw at that circuit. It is 0,6A when crankcase heater is on and 0,1A when is off.
I charged call out fee and leaved site.
Few days later, some electrician called me on phone that he is at site (because I am unavailable for 2 days) of above chiller and that fuse SF2 is blown again. He changed fuse again and started chiller but water pump doesn't work.
I guided him to check SF4 and he found that SF4 (4A found on site) was blown. He changed fuse with new one. Now chiller has worked fine again.
Customer insisted that I came to site later to check if something is wrong.
I checked currents of both circuits and found OK (current on SF2 is same as before and current at SF4 is 3,4A what is normal current of pump). I changed fuse on SF4 with bigger size (6A as noted on diagram).
And checked for loose cables and reaction on high vibration and simmilar. Everything is found OK.

I checked voltage and balance of phases at startup and when in normal operation and everything is in tolerances!

I charged call out fee and leaved site.
Few hours later I got call from upset husband asking me "how I could charge his wife for nothing to be done".

What is your opinions about what could be wrong with electrics when I could not find any problem and what you think about customer complaint about charging him for nothing.


I am specially intrigued at fact that second time 2 non-depended, and on different phases fuses, has blown.
Chiller is 4 years in operation and has newer got problems with fuses!
Fuses are this type: gG 8,5mm x 31,5mm


This is shematic diagram:

[Electrocoolman]

Hi Nike,
Have they (your customer) had any power fluctuations or perhaps power surges? Any one else on same power feed had problems - ask neighbours.

Have you checked insulation resistance of circuits being fed by fuses? Any signs of water ingress into electrics that has dried up by time you get to site?

Have you tried replacing fuses with aM rated fuses as alternative to gG? (Motor and transformer rated) - both fuses feed these loads.

Fuses do 'age' and can blow for no good reason apart from a small surge.

A callout charge is to cover your costs of getting to site. You can include a limited time on site for diagnosis.
For goodwill why not offer to attend for free next time (i.e. waive callout charge, but not labour) if unit continues to give problems.

[nike123]

Hi Nike,
Have they (your customer) had any power fluctuations or perhaps power surges? Any one else on same power feed had problems - ask neighbours.

I asked and they say no!

Have you checked insulation resistance of circuits being fed by fuses?

No, if insulation is damaged I expected that fuse will blow immediately after replacement of fuse or after some part is energized.
I leaved that as last option.

Any signs of water ingress into electrics that has dried up by time you get to site?

No!

Have you tried replacing fuses with aM rated fuses as alternative to gG? (Motor and transformer rated) - both fuses feed these loads.

No because they worked fine 4 years and I don't want to make any alternations until i find reason for their burn out.

Fuses do 'age' and can blow for no good reason apart from a small surge.

Yes, I know that, and that is partial reason for me to still charge the customer even there is no "repair" done.

A callout charge is to cover your costs of getting to site. You can include a limited time on site for diagnosis.

I done exactly that!

For goodwill why not offer to attend for free next time (i.e. waive callout charge, but not labour) if unit continues to give problems.

I offered immediate return of money for last two cals if he think that I charged him for nothing if it happen again or if he things that is the way I should do.
He said (still angry) that I will charge him less ( amount for last call) next time when I came to seasonal preventive maintenance.
He was pleased before this event with my services but now, he thinks that I riping him of!

[nike123]

What you think about this fact?
To me looks like some problem with power supply!

I am specially intrigued at fact that second time 2 non-depended, and on different phases fuses, has blown.

[Gary]

This is the sort of thing that can drive a service tech crazy.

You might try a UV temp tester in the power panels. Sometimes you can identify poor connections and/or burnt contacts as these may show up as hot spots.

[TRASH101]

Hello Nike,

Out of curiousity where/what does LR2/-B7.1 (label -heaters outlet) go/do.

My first thought would be the pressure switch (possible short to earth from case) or solenoid valve.

The pump fuse may be unrelated but assuming its part of the same fault it might be worth monitoring flow, run current and winding temp as reduced flow might flag up your LP etc..

[TRASH101]

You could always segment LR2 circuit with inline fuses sized for individual components

As for the customer............

Sometimes there is no pleasing some people.
They probabley would not even thank you for your kidney unless they saw you stitch in yourself.

[Pyr0Beast]

No, if insulation is damaged I expected that fuse will blow immediately after replacement of fuse or after some part is energized.
Not necessarily. It may be damaged and loose wire touching some grounded part and making a short every now and then.
With the glass fuses you could see what kind of a short it was. If the wire was blown to pieces it was most probably a short. If it was just 'cut' it was caused by exceeded current rating.

Actually, what i think happens is the neutral wire gets loose, current rushes thru MP backwards (or forward, pick one) and exposes the equipment to 380V between phases thus burning (both) fuses.
Has happened before.

.... on a side note, this diagram is a bit faulty. For example, there is no protection for motor (NC) if one phase falls out.

[Pyr0Beast]

This seems to occur when NC and MP are online at the same time.

[frank]

When I come across a brain teaser like this, I usually inset some temporary inline fuses or mcb's to the individual parts, i.e. one to the sol valve, one to the fan motor, etc.

i know it's long winded, but unless you stop on site 24/7 monitoring, it can prove really helpful in identifying the problematic part.

[Thermatech]

I have had solenoid valve coils which test ok & work ok when cold & while monitoring on site.
But if energized for long period while not on site as they get very hot & expand then starting to fail to ground & blow fuse.
When more than one item being protected by fuse then another method like seperate inline fuses can be used to locate the faulty item.

[nike123]

Hello Nike,

Out of curiousity where/what does LR2/-B7.1 (label -heaters outlet) go/do.

Nowhere in this particular case. That is option which is not used in this unit.

My first thought would be the pressure switch (possible short to earth from case) or solenoid valve.

Pressure switch is not on high voltage (220V). It is on low voltage from controller.

The pump fuse may be unrelated but assuming its part of the same fault it might be worth monitoring flow, run current and winding temp as reduced flow might flag up your LP etc..

Low flow will flag up high pressure because it is in heating operation now, but that is not the case here. Also, there is no regulating valves to change flow, it is constant.
Pump current is stable and within specifications.

[nike123]

No, if insulation is damaged I expected that fuse will blow immediately after replacement of fuse or after some part is energized.
Not necessarily. It may be damaged and loose wire touching some grounded part and making a short every now and then.

As I said, I alredy checked for loose wires!

And checked for loose cables and reaction on high vibration and simmilar.

With the glass fuses you could see what kind of a short it was. If the wire was blown to pieces it was most probably a short. If it was just 'cut' it was caused by exceeded current rating.

Unfortunately, these are not glass fuses!

Actually, what i think happens is the neutral wire gets loose, current rushes thru MP backwards (or forward, pick one) and exposes the equipment to 380V between phases thus burning (both) fuses.
Has happened before.

Could be easily.

.... on a side note, this diagram is a bit faulty. For example, there is no protection for motor (NC) if one phase falls out.

Diagram is as OEM has decided to make his equipment.
If one phase is faulty, then other two will overheat and internal thermal protection of compressor will act! It is some form of phase failure protection, though not the best one.

[nike123]

When I come across a brain teaser like this, I usually inset some temporary inline fuses or mcb's to the individual parts, i.e. one to the sol valve, one to the fan motor, etc.

i know it's long winded, but unless you stop on site 24/7 monitoring, it can prove really helpful in identifying the problematic part.

I have had solenoid valve coils which test ok & work ok when cold & while monitoring on site.
But if energized for long period while not on site as they get very hot & expand then starting to fail to ground & blow fuse.
When more than one item being protected by fuse then another method like seperate inline fuses can be used to locate the faulty item.

Thanks Frank and Termatech, good advice!

[Pyr0Beast]

If one phase is faulty, then other two will overheat and internal thermal protection of compressor will act! It is some form of phase failure protection, though not the best one.

If feel sorry for the compressor already ..

[Pyr0Beast]

I*
.. sorry for the double post.

[TRASH101]

Pressure switch is not on high voltage (220V). It is on low voltage from controller.

I meant the pressure switch marked AP on page 2 which shows it as a neutral interrupt in conjunction with MV1.

Don`t forget who mentioned the inline fuses first.

[nike123]

I meant the pressure switch marked AP on page 2 which shows it as a neutral interrupt in conjunction with MV1.

Yep, you are right and I am wrongly thinking that you think that BP on page 3 is what you speak about.

Don`t forget who mentioned the inline fuses first.

Yep, again!

[frank]

Don`t forget who mentioned the inline fuses first.

Great minds think alike

[nike123]

Update guys!


Yesterday, when I was having afternoon nap (yes, it is Sunday afternoon ) I got call that this fuse is blown again.
When I came to site I checked current draw at that circuit and found that current draw is lower than I expect when compressor is at standby. Then I checked crankcase heater resistance and found that crankcase heater resistance is infinite.
There it is, my cause of problem is finally burnt.
Probably, before it have intermittent short with heater housing when it is hot and that will burn a fuse.

Funny thing is that it worked last month with no problem till yesterday.

[Pyr0Beast]

Everything works until it stops working

[nike123]

Everything works until it stops working

Yep!
Could I use that as my signature, please!

[Pyr0Beast]

Yes, no problem.

Glad to hear you finally figured out what the problem was

[nike123]

Glad to hear you finally figured out what the problem was

We will see that in future.
Who was once bitten by snake is frightened even by lizard.

Original: Koga zmija ugrize i guštera se boji.