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

[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.

 

[GBDamo]

The fact that it is not tripping on start up rules out the MCB. Fitting a C or D type would be masking a problem that will sooner or later start tripping a C or D

Get a clamp meter on the live at the CU and look how it’s drawing current. If you see the start up spike followed by a drop off then a slow creep back up until trip then it’s probably one of three things.

1, Bad run cap, or relay stuck in the soft start.

2, build up of detritus on the outside coil,

3, low gas.

It’s highly unlikely to be the fan or the compressor.

But to discharge you’re responsibility just clamp the feed and demonstrate it is drawing more amps that design.

 

[ipf]

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.

Only a point, Pete. I just don't like completing an industrial/commercial kitchen, all to spec, only to return and find SY strung around, including inside DB's, after they've been in to do their little bit. Not always, but sometimes, they seem exempt because they're coming in last. Please note, most of these are not engineers, just installers.

 

[kevincoolnomix]

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.

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.

 

[kevincoolnomix]

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

The problem is likely doe to compressor short cycling. This is due to either a lack of refrigerant or (more likely) the condenser fins outside are blocked and the unit therefore cannot get rid of enough heat (a bit like a car radiator overheating). As a result the compressor will shut down on high temperature/high pressure and then attempt a restart while there is still a significant differential pressure across the compressor. The resulting load is just too much for the MCB and it will trip. The solution is first to clean the outside condenser fins and then top up the refrigerant (as a lot of this will have vented to atmosphere through a high pressure relief valve).

 

[Pete999]

The problem is likely doe to compressor short cycling. This is due to either a lack of refrigerant or (more likely) the condenser fins outside are blocked and the unit therefore cannot get rid of enough heat (a bit like a car radiator overheating). As a result the compressor will shut down on high temperature/high pressure and then attempt a restart while there is still a significant differential pressure across the compressor. The resulting load is just too much for the MCB and it will trip. The solution is first to clean the outside condenser fins and then top up the refrigerant (as a lot of this will have vented to atmosphere through a high pressure relief valve).

Never seen an A/C system with a built in refrigerant relief valve that vents dangerous refrigerants cfcs to atmosphere, as it's a sealed system, more likely to be a leak via a loose or bad joint. A properly installed A/C system will have been filled with refrigerant, using a gauges and scales. Most A/C systems have HP and LP controls which will shut the unit down due to either condition, and allow the refrigerant pressure to equalize, NOT vent it to Atmosphere.

 

[Pete999]

Only a point, Pete. I just don't like completing an industrial/commercial kitchen, all to spec, only to return and find SY strung around, including inside DB's, after they've been in to do their little bit. Not always, but sometimes, they seem exempt because they're coming in last. Please note, most of these are not engineers, just installers.

Sorry for the late reply ipf, I know how you feel, looks bluudy awful doesn't it, you could say, well I didn't do it, but being the Electrician on site, it will almost always be attributed to you, awful stuff, cable tied every where. As you say Installers not engineers.

 

[The Ghost]

The problem is likely doe to compressor short cycling

Thanks for the input @kevincoolnomix. Air Con is not within my skillset and it is a discipline outside of my ken. I was only there to rule out the supply circuit contributing to the problem. As already stated, the manufacturers told me that the unit should be fused to allow for a draw including inrush currents of 61-80a. So at 20a that was not going to cut it. I have in fact put in a 32a MCB type B. Although I had a type C just in case I was loathe to put it in as the EFLI may not have complied with a type C. At this time I cannot check the Zs as I can not get to the outside unit (furthest point) to check such things. I have an arrangement to get there but it is when the people upstairs grant access to measure Zs to ensure it complies. So far the 32a MCB has not switched off and the unit is working fine.

 

[Toneyz]

What size cable is it? we always fit C type MCB's based on the label plate on the unit and have no problems, is this one with a feed to an isolator at the outside unit. As you know what Ze is you could take a good guess of the cable run and work out R1 + R2 to give an approx EL I for the MCB. The shop should have got access for you originally so that you could have tested prior to energising.

 

[Pete999]

Thanks for the input @kevincoolnomix. Air Con is not within my skillset and it is a discipline outside of my ken. I was only there to rule out the supply circuit contributing to the problem. As already stated, the manufacturers told me that the unit should be fused to allow for a draw including inrush currents of 61-80a. So at 20a that was not going to cut it. I have in fact put in a 32a MCB type B. Although I had a type C just in case I was loathe to put it in as the EFLI may not have complied with a type C. At this time I cannot check the Zs as I can not get to the outside unit (furthest point) to check such things. I have an arrangement to get there but it is when the people upstairs grant access to measure Zs to ensure it complies. So far the 32a MCB has not switched off and the unit is working fine.

What is the distance fro the inner unit to the outside unit?

 

[Toneyz]

What is the distance fro the inner unit to the outside unit?

Not knowing much about A/C when we installed supplies to these outside units the A/C guys lashed in (sorry installed)small flexes to the indoor unit is there not internal fuses protecting these?