Air con blowing 20a MCB a few weeks into box change in shop/commercial

[The Ghost]

Strange day, changed DB in shop couple of weeks ago from old wylex with cooked neutrals and burnt out neutral bus. Wiring was the usual sargasso sea of cables above suspended ceiling, old circuits, redundant circuits and really bad light switch arrangement. Pulled out the switch wires (six) and re-located into grids at reachable height and so on. Fully expected to be called back for RCD problems.
Got a call regards the air con MCB popping a couple of weeks in. Thought mhmm just megger cables (SWA) and flexible control cable from outside fan to unit. Not possible as could not disconnect or access cables on outside unit. I suspect the outside fan is jamming but can't even look at it as it is inaccessible. Do not really know about air con apart from the obvious general principles. Anyone up on air con? Its a Fujitsu in suspended ceiling quite old by the looks of unit.

 

[Pete999]

Older a/cs can be quite brutal on start up and of course the compressor drops in and out frequently. Best bet is to c or d curve and to max of cable capacity.

Any of the filters blocked? this can cause the compressor to work overtime, what temp does the unit produce at the evaporator outlet?

 

[Toneyz]

It needs a C curve MCB due to an inductive load.

 

[littlespark]

Here cometh the "But it worked before you touched it" bolux from the customer

 

[Octopus]

Is there not a DP isolation switch?

 

[The Ghost]

Is there not a DP isolation switch?

Not that I can see but can't get to outside where the outside unit is which is where all the business is like compressor and heavy duty fan.
Thanks again for the input it appears you are all spot on! I spoke to tech. dept. today for Fujitsu. They told me it is an obselete fifteen year old model and as stated by @plugsandsparks are brutal on the inrush side. I was told the initial draw is at least 61a so undersized on the 20a they recommended type C at least 25a or 30a. They also said it has probably been regassed with a substitute gas reducing the efficiency by up 30% considering age of the components and the gas is banned (R2 gas) since 2014 and re-filling it with that would attract a hefty fine/imprisonment! There was no info on the exact model but the guy seemed to know it well and was great, really chatty. So I have learnt a few things which is great. And thanks all again.

 

[The Ghost]

Any of the filters blocked

Pete I don't know to be honest. It is due for service so no doubt that will be checked but that is outside my skillset and competence so I left that side of it all well alone.

 

[The Ghost]

Here cometh the "But it worked before you touched it" bolux from the customer

Yep had that already from the customer. Basically due to lack of info on rating. I have underrated it. But all's good as now I know I can fix that and no cost to customer just a small amount for the type C MCB.

 

[Pete999]

Not that I can see but can't get to outside where the outside unit is which is where all the business is like compressor and heavy duty fan.
Thanks again for the input it appears you are all spot on! I spoke to tech. dept. today for Fujitsu. They told me it is an obselete fifteen year old model and as stated by @plugsandsparks are brutal on the inrush side. I was told the initial draw is at least 61a so undersized on the 20a they recommended type C at least 25a or 30a. They also said it has probably been regassed with a substitute gas reducing the efficiency by up 30% considering age of the components and the gas is banned (R2 gas) since 2014 and re-filling it with that would attract a hefty fine/imprisonment! There was no info on the exact model but the guy seemed to know it well and was great, really chatty. So I have learnt a few things which is great. And thanks all again.

The only reason any refrigerant is required, is if there has been a leek in the pipework, as for the excuse replacement gas that's horse poo, the /C equipment will have been designed and set up for a particular Refrigerant, I think they are talking about R12, which has now been outlawed, almost like the garage telling you that a top up of Gas is required, more BS if the system has been installed properly the the refrigerant, should last for the life of the A/C unit, far to much BS spoken about refrigerants.

 

[plugsandsparks]

I do a/c , if its been re-gassed, will be probably from squirrel stock. Pressures are very low on the old stuff so a small leak can exists but take years to have an effect and they are hard to find hence many a/c engineers top up the gas. Easiest way to test it in your situation is with a thermograph temp device like the Flur, Set a/c to cold, max fan and measure temp of air coming off, anywhere between 5-10 degrees is what you want to see.

 

[Pete999]

I do a/c , if its been re-gassed, will be probably from squirrel stock. Pressures are very low on the old stuff so a small leak can exists but take years to have an effect and they are hard to find hence many a/c engineers top up the gas. Easiest way to test it in your situation is with a thermograph temp device like the Flur, Set a/c to cold, max fan and measure temp of air coming off, anywhere between 5-10 degrees is what you want to see.

What you need is a refrigeration High and Low Pressure gauge set thermometers etc to set up an A/C system relying on temp off is a quick fix method, what people don't seem to understand is that, is that HVAC is a Trade on it's own, don't muck with it if you don't understand the dangers, and believe me it can be as dangerous as a Chippy , Plumber messing with electrical work, I was lucky I took many A/C courses, but I would never in the world consider myself a competent Fridge Mech.

 

[westward10]

Think this is a case of fitting the wrong protective device

 

[ipf]

What you need is a refrigeration High and Low Pressure gauge set thermometers etc to set up an A/C system relying on temp off is a quick fix method, what people don't seem to understand is that, is that HVAC is a Trade on it's own, QUOTE]


Aye, it's a trade on it's own....that's why they're always doing our part of the installation......and feeding badly with SY, for ease.

 

[Pete999]

Think maybe you are giving Fridge Mech the wrong signals IPF, it's what they have bee taught to do, up to the likes of us to put them right, OK they may be using inappropriate cabling, but then again so do many new Sparkies don't they, I have had Fridge Mech come away with me on trips overseas solely because they know far in excess of my understanding of A/C systems.

 

[Marvo]

Most of the old A/C unit were on freon 22 which from memory was classed as an intermediate gas for phasing out so probably not available anymore in the UK although it's still available in infinite quantities where I am.

If a new generation drop-in replacement gas has been used in it then efficiency could be negatively affected by a few percent but it wouldn't change the compressor start current, only the run current. Any gas issues including over-charging, under charging, incompatible gas and even under condensing issues won't have any effect on start current until such a time as eventual mechanical damage occurs to the compressor but you'd hear the rattling or notice it was locked rotor immediately when it runs.

As already advised don't under any circumstances get involved, replace breaker and ride off into the sunset.

 

[The Ghost]

As already advised don't under any circumstances get involved, replace breaker and ride off into the sunset.

Sage advice indeed. You may rest assured I never step past my level of understanding/competency too aware of liability. Where I don't know I tell the customer and suggest getting in someone who specialises in the field whatever it may be.