MarineAir air con problem

[Andy Cox]

Hi
Newbie here from Cornwall.

I have recently purchased a Trader 45 which has three separate self contained reverse cycle air con units. I'm struggling with the midships unit, as within 10 seconds of turning the breaker on, it is popping the 16A MCB fitted between the 240/110 transformer and the unit itself.
I' don't know a lot about air con systems, but I'm learning fast and I'm wondering if the compressor has seized, as these units haven't been run for some time and hence a high current draw exceeding the MCB rating.
Any thoughts or suggestions would be welcomed and perhaps some advice on how I can check the compressor itself.
Thanks
Andy

 

[Andrew M]

I guess there could be any number of explanations originating with the AC units as you point out and I'm not that au fait with the units to comment, however, we were regularly tripping a breaker (not one for the AC) on our boat a couple of years ago , I kept checking everything on that circuit and couldn't find anything wrong and eventually whittled it down to the breaker itself becoming weak or too sensitive to the loads. It might be worth replacing the breaker or at least swapping it with another of the same rating just in case it's that ?

 

[jrudge]

If the other units are off then a series of things should happen when you turn it on.

1. the water pump should start so the condenser is cooled

2. the fan on the unit will usually start immediately ( you can make it so it only comes on with cooling / heating in settings so this may not happen - but if not check settings and adjust so it does.

3. the compressor will start. They will all have different stage delays on them that stops your shore power being hit with 3 compressors starting at the same time.

How far do you get in this 10 seconds?

If the unit is off then if you push the fan button the fan should come on without AC. Does it - or does that blow it. In which case fan motor or fan capacitor ( see below) .

If the fan works and the water pump works ( assume it does on the other units) then the bit left that takes electric is the compressor. It should be quite obvious when if kicks in.

You could go into settings and see what stage delay is set. If 10 seconds then make it 20 seconds and see what happens. Does it now trip in 20 seconds? This would prove to some degree that it is the compressor.

The compressor has a large capacitor. These do go over time and is the cheaper thing to change. If it is the capacitor I would think that you would see / hear / feel some momentary compressor movement before it tripped ( I am not totally sure on this) which would prove if it were seized. You could swap a capacitor from a working unit and see what happens.

https://www.youtube.com/watch?v=ApnxMvmTEwQ

Video link to show you what you are looking for.

Failing that call in the local AC man ( which I appreciate is probably more tricky in Cornwall than in Palma where there are about 20 of them available 24/7!)

 

[Portofino]

A light tap with a mallet ,or a few woodpecker taps after turning it on within the 10 sec before trip period .
May unstick the comp ?
If it gets hot within the 10 or so secs before tripping out then it’s stuck I reckon .

 

[superheat6k]

Some very good advice here.

Here is what I would do for fault finding.

1 Do you hear the compressor actually run, or perhaps buzz ?

If it runs does the discharge pipe start to get hot.

2 Place a clamp meter on the supply leads to the compressor motor (normally there will be three)

Run The main driving current should start high them drop down within a couple of seconds

Start This starts quite high then drops to a low level typically 1/5 to 1/3 the Run current

Common Almost the sum of the Run and Start, but due to phase shift in the start winding they do not add up fully to the actual value of both added. Please don't ask me to explain here about phase shift.

The Common current should settle well below the trip rating within a few seconds.

The MCB should not trip below the rated current, but as mentioned these can weaken especially after a long hard season working hard in hot weather.

So no current on the start connection possibly a duff start capacitor - typically ~10 - 20 uF. Simply try a new capacitor

What are the motor field coil resistances

Lowest R > C e.g. 2-5 ohms

Medium C > S e.g. 8-12 ohms

Highest R > S e.g 10 - 17 ohms

The RC & CS should add up to the same as RS, but meter lead static resistances can distort low value resistance measurements, so measure this and deduct from each reading.

If the run current and start current are quite high and the compressor does not turn with a few seconds then yes - duff (seized) compressor. If the start current is not present then duff cap or start winding. If any field open circuit, also duff (compressor motor winding).

This might help (single phase and fault finding section). A while since I wrote it, but the principles haven't changed ...

https://www.dropbox.com/s/qhkkox4xfaoqc5o/ThermaCom Field Compressor Guide.pdf?dl=0

 

[Andy Cox]

Hi All and many thanks for the helpful advice.

This boat was originally specced for the Caribbean and when she was imported the owner had transformers fitted to run the the Air Con systems. At the AC electrical distribution panel, there are four breakers relating to the Air Con, one for each unit and the fourth for the water pump. Each breaker supplies 240v to the relevant transformer and then 110v from the transformer, via a 16A MCB to the Air Con unit. I would guess this is a fairly typical set up for a boat imported from the North American market?

I was running tight on time when I looked at it on Tuesday, but the fwd unit, which is fully functional, seems to go through a 'start up' sequence when the power breaker is first switched on. First the Passport II panel lights up and a fairly loud clunk sound is heard from the air con unit, it sounds very much like a heavy duty relay latching in and I assumed this is the reverse cycle changeover relay? Then the control panel goes off and the relay goes off. The system is then ready to go and pressing the on button on the panel fires it all up and away it goes. The water pump runs fine and I recently removed it, serviced it and test ran it with no problems and I've got a good flow from all three outlets.

Does this sound like a typical scenario for a Marine Air unit?

My impression is that the midships unit isn't completing the same 'start up' sequence and something is stalling and generating a high current. I had considered the possibility of the MCB being weak and tripping early and I'll swap it out to check this.

I'll get back to the boat in the next couple of days and do some more extensive testing with the help of all your information and will let you know how I get on.

Sorry if this is a bit long winded and thanks again for all your help.
Cheers
Andy

 

[jrudge]

I have had split units for a while.

I dont recall a clunk, but if that unit works then i would not worry about it.

I believe mine panel does come on when power is applied and then go off, but again i cant be sure as i don't really pay much attention. Again that one works so assume it is fine. You have three ...what does the other one that works do?

The unit that causes the issue - from what you have said this one is tripping before you even turn it on ( ie the controller is turned off which then will preclude the fault finding steps I listed.

If you have transformers this is also another possible point of failure. Get your volt meter out and see, or power it off another transformer which at least will eliminate it as a source of issue ( and at the same time prove or disprove the breaker faulty theory if it pops with the other transformer as well.

See how far you get.

 

[Andy Cox]

Just wanted to say the problem is now resolved and a big thanks to everyone who chipped in with help and advice.

I put a new 16 amp double pole C type MCB in place of the old MCB, which interestingly enough was a B type which has a lower trip setting on start up than the C type.
My guess is that the old breaker had weakened enough, that when combined with the lower start up trip rating was causing it to pop every time.

All the air con / heat units are now working a treat and I should be able to coax SWMBO on board!

Thanks again
Andy

 

[Andrew M]

Good, well done sorting it. it's a nice feeling when you get something sorted with a nice simple fix.


As you've got reverse cycle, I would recommend regularly turning on all the units and going through the "cool" to "heat" to "cool" to "heat" and leaving them to operate for a short while in each phase, it helps ensure the reverse cycling valves don't seize in any one position which is one of the more common a/c issues.

 

[superheat6k]

Good, well done sorting it. it's a nice feeling when you get something sorted with a nice simple fix.


As you've got reverse cycle, I would recommend regularly turning on all the units and going through the "cool" to "heat" to "cool" to "heat" and leaving them to operate for a short while in each phase, it helps ensure the reverse cycling valves don't seize in any one position which is one of the more common a/c issues.

This is excellent advice. If you experience breaker trips again then fit D curve, but be aware many pontoon MCBs are C or even B curve.

 

[Andy Cox]

Thanks Andrew M, you're right, it is a good feeling being able to sort something out and cross it off the list........... yes, a list, surely everyone has one........don't they??

I've read that in the manual about the possibility of the valves seizing so I will be 'exercising' the reverse cycle valves regularly.

Superheat6k, again thanks, that is useful, as I hadn't considered the trip curve at the pontoon. I try and use a 32A supply wherever we are so hopefully the pontoon tripping out is unlikely. However if we're on a 16A supply then I do need to be careful, as we are totally electric and have no gas on board, so tend to rely on the 12kv genny quite a lot when a 32A supply is unavailable.
Andy