Are you sure it only has that problem at night, rather than you only notice it at night?

If F4 is indicating a water flow problem, how is it sensing that? Is it a flow switch that is actually sensing water flow, or is it a high pressure safety switch, and the fault is actually a high pressure fault in the refrigeration circuit? Find all of the safeties on the system and make sure wiring connections are tight.

The really strange part is that it only happens when you go to bed. Does it happen at night if you are NOT in your bed? Do any hoses pass under your berth? If so, is it possible that your weight on the bed is pinching a hose and restricting flow? (Just throwing ideas out there!)

When you measure flow into a bucket you get sufficient flow, but if the restriction is in the through hull you won't see it. If you run a hose overboard and run it for longer periods does the problem go away? Another way to check water flow is to measure the temperature of the water into the condenser and compare it to the water outlet temp. If there is a large temperature rise, that is an indication of low flow.

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Since all runs fine during the day it isn't a scale/clogging type of water flow related problem. Does the forward unit also shutdown? I bet it isn't a water flow problem as much as it is a electrical power problem dropping out the water pump. What is the power doing during the night?

 

I think you have some moisture in the gas lines. As the outside temp decreases a few degrees at night, this allows the moisture to freeze at the expansion valve and stop the gas flow. If this is so, the system will need to be drained of gas and a vacuum pump placed on it for some time, then refill and watch the gauges settle after running a while. I don't know the figures for your systems, but a good refer tech should.
You could possibly see the water bubbles in the sight glass, but that is a maybe.

 

Thank you, gentlemen, for these replies.
SchockT:
Yes, as I said it only happens at night. Both units are fine during the day. I don’t know if it happens when we are not there overnight, since the AC is not on then.
The aft unit discharge does indeed pass under the bed, but there is absolutely no restriction when lying on the bed. The outlet cock is actually larger than the outlet hose, with full uninterrupted flow. There is no change in the outlet flow, day or night.
Don L:
The forward unit runs flawlessly during the night, supplied by the same pump as the back unit. The voltage to the pump does not change at night, according to the voltmeter on the master board.
Capta:
There are built-in high- and low-pressure gages on this unit, but I’m not sure how to read them to check your hypothesis. I have thrown these suggestions back to the makers and waiting their reply. I am absolutely sure it is not a physical water flow problem, but something might be telling the electronics that is it.
Any other suggestions would be most welcome. It’s driving us nuts.
JR

 

E4 is a high pressure fault. Lack of enough cooling water is one cause, but there are others like a dirty condenser or filter, blocked air flow, etc. Sounds like you've checked all but blocked air flow. Is there something about going to bed that changes this, like a blanket laying over an outlet, or inadvertently setting something on one?

Capta's suggestion is the best so far.

Mark

 

Hi Colemj:
Missed your post until now.
I thought about air flow, but it still fails even when I remove the filter in front of the evaporator. Otherwise no air restriction at all.
JR

 

Flow in is only half of it - there needs to also be a minimum area for outflow. If one of the vents gets blocked, the flow reduces and pressure builds. I mention this because we have units with several adjustable flow vents and every once in a while one of them shuts itself, which is sometimes enough air flow reduction to trip the high pressure switch.

Mark

 

Airflow will not cause a high pressure condition in cooling mode. If you are running in heating mode then it could happen.

If the unit is equipped with built in gauges then you should be able to monitor the high side and see if head pressure is going up when the problem occurs.

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Now that you mention it, the last time it happened was in the winter while in heat and we had it happen several times, but not since in cool mode.

Mark

 

Hi Colemj:
Yes I understand. Air outflow through all the vents is unrestricted and both units are very similar, being 8” x 4” straight trunking, with spurs off to the cabins and bathrooms. No restrictions there. In fact the aft trunking only has one 4” square vent into the aft bathroom, otherwise straight into the bedroom and saloon. You can see straight through the vents.
I should add, the machine worked perfectly until about three months ago, when this strange performance began.
JR.

 

Let me give you all the website for Marinaire, and maybe you might be able to glean something from their specs.
Mareinaire.com
Mine is the 16,000 Btu size.

 

So it looks like your system uses a capilliary tube metering device, and has no liquid receiver, which gives Capta's theory some merit, although it begs the question, how did moisture get into the system? You said it is a fairly new system, so likely has never been opened up or serviced in any way. That said, there are other conditions that can cause restrictions in a cap tube system.

Of course none of those things would only happen at night. I think it is best to put the idea that it only happens at night aside for now.

The good news is that the problem is repeatable. The next time it starts to happen you need to watch your pressure gauges. Under normal operation you should see a low side pressure somewhere in the range of 100-120psi and high side should be around 310psi. Also make note of the temperature of the liquid refrigerant pipe coming off the condenser. It should be slightly warm, but not hot.

When the unit starts to misbehave, check your pressures. If you see the suction pressure dropping well below normal, and at the same time the high side pressure climbing above normal, then you likely have a restriction in the system.

If the head pressure climbs but the low side stays the same, or rises you likely have a water flow problem. If that case you will also find the liquid refrigerant pipe gets hotter too.

If the unit trips on high pressure while you are monitoring it, and you didn't observe a rise in pressure on the high side, then you likely have a faulty high pressure safety switch, or a bad connection on the safety circuit.

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Thanks again SchockT. You are getting a bit out of my expertise, but I’m sure I can do what you suggest, except it will probably be around midnight. I can't get to the inside of the unit though. As you will see on the website it is all encapsulated and it's also mounted in a tight space in the boat.
The machine is now just over one year old and warranty is 1 year – wouldn’t you guess?
I must state again. Whenever the unit trips E4 is ONLY AT NIGHT, never during the heat of the day. If you ask me, that’s where the conundrum lies? I’ll let you all know what the makers say.
JR

 

Thanks again SchockT. You are getting a bit out of my expertise, but I'm sure I can do what you suggest, except it will probably be around midnight. I can't get to the inside of the unit though. As you will see on the website it is all encapsulated and it's also mounted in a tight space in the boat.
The machine is now just over one year old and warranty is 1 year - wouldn't you guess?
I must state again. Whenever the unit trips E4 is ONLY AT NIGHT, never during the heat of the day. If you ask me, that's where the conundrum lies? I'll let you all know what the makers say.
JR

So you cant even see the pressure gauges on top?

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Oh yes! I even left a cut-out in the front panel, just to be able to inspect them. I'm not going to be on the boat until next weekend, and I hope to get a reply from the makers before then, to all your suggestions. I've got to get to he bottom on it somehow.

 

Gentleman:
Just a quick note to say I went over to my boat yesterday and the AC ran perfectly all day, with the correct psi on the gages. Water temperature is 88°F.
I wasn’t able to stay overnight, so I couldn’t check what happens when it breaks down, but I will in a week or two.
Thanks JR

 

Gentlemen,
Sorry for the long delay, I finally managed to watch the effect as the aft AC went into E$ fault. It happened at 3am last night. Here is the story, as best I could observe it on the built-in gages:
Both forward and aft AC’s running normally, 73°F each 56% humidity.
Compressor stops on aft unit; forward one continues to work normally.
Aft unit, high side goes up to about 600psi.
Low side is steady at 230psi, then slowly rises to about 350psi.
High side then drops to about 300psi.
After a few minutes the compressor starts up again.
High side rises again to 600psi.
Low side remains about steady at 230psi.
The machine then shows E4, lack of water flow and we switch it off.
We have an amateur theory: The two AC units share a common pump, the outlet being divided with a Y valve, like used for twin water hoses. When the units drop to 73°F at night, (they never go that low during the day in Florida summer heat), will the forward unit tell the pump to slow-down, thus causing a reduced flow of water through the rear unit, triggering E4?
All suggestions greatly appreciated. we need to sort it out asap.

 

My guess is that the forward unit is controlling the pump, and when it cycles off it shuts the pump off.

You are definitely losing flow, and the pump shutting off would explain it.

You need to figure out where the pump is getting it's power from, and figure out how to ensure it will continue to operate as long as either unit is running.

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Have you tried to run only the aft system to be sure the water pump relay is getting trigger by it

 

Thanks, SchockT.
I think you might be getting nearer.
The power comes in to each unit on completely separate 120-volt shore power cables.
However, the rear unit actually goes to E4, even during the day, whenever we switch the forward unit off, which bears out your prognosis—the rear unit is probably not actually connected to the pump. I bet that’s it!
So, what I need to do is wire the aft unit also to the pump, so each unit keeps the pump running separately, even if the other unit is switched off. Yes?
Is it normal for a marine AC to stop, or slow the pump, whenever the compressor cycles off, especially when it has reached the lowest temperature it is set for? That seems logical, if only to save power.

 

Yes I would think that most units would only energize the pump when needed.

The question is, does the pump get line voltage from the A/C unit, or does it have it's own relay that is energized by control voltage from the A/C?

How the unit controls the pump will determine how you correct the problem.

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Thanks, Don L
I can’t say we have, but I bet the rear unit is not actually connected to the pump relay! But that must mean the forward AC actually cycles the water pump on and off, causing a reduced flow to the rear unit?
So, what I need to do is wire the aft unit also to the pump relay, so each one keeps the pump running separately, even if the other is switched off. It seems logical that each should activate a common pump?

 

Don L’s question is a bit embarrassing to answer truthfully. I haven’t tried that, which is a bit elementary when you think about it, but I’m only a simple sailor.
I will not be back at the boat until the weekend, when I will thoroughly investigate how they are both wired.
Thank you both for your help so far.
JR

 

I looked at the wiring diagram for your unit and it looks like the unit has line voltage output for the pump. (Terminals PL and PN )

It is unclear whether you could run a parallel circuit from the other unit to the pump since the diagram doesn't show how the control board switches that circuit, so you should consult the manufacturer about that.

If you are not comfortable doing line voltage wiring yourself you should have an electrician correct the problem.

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It's not useful to the OP's wiring solution, but I can add that we have a common pump for separate AC units. The pump is on a dedicated circuit breaker, but it only cycles on when each individual units comes on. I've never checked the thru hull flow, but suspect both units get raw water circulated, even if only one wants it.

 

Seems like it would be simple enough to cut out the circuit slowing down the pump. I've run many dual or even three systems on a single pump, without that circuit. Even with one or two units not operating, the water flow through them should remain constant.
If you don't have one, contact the company or any qualified refer mechanic for a copy of the schematic and it should be easy from there.

 

I don't see any indication that it is a variable speed pump. I suspect the pump shuts down completely. Depending on how the control board functions it may be a simple matter of running a set of wires from the second unit so that either one will energize the circuit. If the board has a separate relay or triac to turn on the pump that shouldn't be a problem. On the other hand, if the pump is being energized off the same relay as the compressor you could end up energizing the compressor on unit 1 through the pump circuit of unit 2.

Another option is to have the pump on it's own circuit and turn it on manually when using the a/c, but that means you need to remember to turn it on and off.

Either way there is a simple solution that any technician or electrically savvy owner can sort out easily.

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My wife and I do so appreciate the effort and help with this problem, and I think we might be near a solution, one way or another.
I’ll go over to the boat, maybe Thursday, to look at both installation schematics, and see if I can sort it out. I’m only a self-taught electrician, and I don’t want to blow anything up. So If I can’t understand it, I will scan the diagrams and post them here. I’m certain someone will show me how to do it.
JR