Cruisair pressure problem

[davechili]

I have two selfcontained units using one pump. Water is pumping thru both loops when bow unit is operating. However I am getting high pressure indication on stern unit after operating for some time. The water pump will not come on when only the stern unit is on.
Could this be the reason for high pressure at stern when both units operating ?
Why would the stern unit not turn on pump?

[a64pilot]

I'm going to guess two things one that your pump is not big enough for both AC's and or the plumbing is keeping enough cooling water from the rear and that your pump is not wired for the rear one to power it.
If it were me I'd install a second dedicated pump to the rear AC. Pump failures are common and if it does you lose both AC's


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[transmitterdan]

When anything changes like this ask yourself what externally has changed since it last worked. Your answer to this may help someone identify the problem.

If stern compressor runs without water flowing you will get a high pressure trip. Typically high pressure trips happen when the cooling water is too hot and/or there is too much refrigerant in the system. When a boat moves from cool water to warm/hot water that can trigger a high pressure trip too even though water is flowing.

There could be other reasons for high pressure trip such as blockage in the system or some component failure.

There could be several reasons why the water pump does not come on when the compressor unit requests water. Maybe there is a loose wire from the stern unit to the pump control module. The way it works is the pump control module receives a command via a wire (or pair of wires) from each compressor unit. When any compressor unit requests coolant the water pump should run so long as any compressor is requesting cooling. The problem could be in the stern unit. There is a circuit board in the compressor unit that generates the signal requesting coolant water. Maybe this board is damaged or a connector has come loose. Check all the wiring for loose connections or connectors not fully plugged in. Look for signs of burning on all circuit boards. Some units have fuses on the circuit board. If you see fuses check or replace them.

If you are not comfortable with a volt meter around mains powered circuits call an A/C repair person. If you are comfortable you can check for the proper voltages based on the schematic diagrams in the maintenance manual.

[ranger58sb]

Originally Posted by davechili

I have two selfcontained units using one pump. Water is pumping thru both loops when bow unit is operating. However I am getting high pressure indication on stern unit after operating for some time. The water pump will not come on when only the stern unit is on.
Could this be the reason for high pressure at stern when both units operating ?
Why would the stern unit not turn on pump?

Our installation is similar.

Usually when one unit displays the high pressure fault code, its because cooling water flow is insufficient for that particular unit. A visible hint to this system is reduced discharge from the associated discharge outlet. You may see water discharging, but it may not be enough. Could be because the system is clogged, or even a plastic bag partially blocking the seawater inlet could be the culprit.

The fix is to clean your sea strainer and flush/backflush the cooling water system, and we occasionally use a flushing product specific to the purpose. (Triton Marine makes one, google tritongreen or something like that; no association.)

It may be something else, though. If the controller for that particular AC unit really doesn't even try to turn on the pump... it may be that it won't do that until cooling water is sufficient. Or it may be the controller/circuit board has developed a fault. I wouldn't leap to that conclusion before eliminating insufficient water flow as the most probable cause, though.

-Chris

[davechili]

I have flushed and cleaned lines thru both units, and have replaced strainer filter. I also replaced lines between strainer and pump.
I think it is related to the compressor not telling the pump it wants water. As long as the front unit is requesting water, all is fine.
Does this make sense to ya'll ? Either trigger in pump relay,or wiring to relay seems logical culprit.

[transmitterdan]

The pump control module has relays inside. They may be mechanical or solid state relays. These relays form an OR function so the pump should run when one or the other of the compressors is cooling. The diagnosis of this problem requires finding out whether the command from the compressor is getting to the pump control module. Then that will tell you whether to look at the pump control box or the compressor for the problem.

[jeremiason]

From a thread in 2008

http://www.cruisersforum.com/forums/...lem-19028.html

[a64pilot]

I still don't understand why you guys with multiple AC' a tie them to a single point of failure. Especially when that single point is the most likely thing to fail. One big pump is not that much cheaper than two smaller ones and of course it's usually a pump failure that disables the AC unit.


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[ranger58sb]

Originally Posted by a64pilot

I still don't understand why you guys with multiple AC' a tie them to a single point of failure. Especially when that single point is the most likely thing to fail. One big pump is not that much cheaper than two smaller ones and of course it's usually a pump failure that disables the AC unit.


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Boat came that way from the manufacturer. Not broke, no need to fix.

Yet.

In this case, it's apparently not a pump failure, since the pump works on demand from Dave's other AC controller. Since it's likely something to do with the AC controller system... multiple pumps wouldn't change that.

If we were to have a pump failure... replacing a single pump is relatively easy (in our case, since access is good). Another thru-hull penetration and sea strainer -- or a manifold to multiple pumps -- plus another pump, plus slightly re-working the plumbing to route from new pump to one of the ACs... Well, lots' o work... compared to a simple one-pump replacement... in a system that's worked according to plan for 12 years. (Ooops, slightly wish I hadn't said that, now...)

I know of boats -- as delivered from the maker -- where one pump supplies 3 and even 4 ACs.

I don't know of anyone around here who has had an AC pump failure; all the failures I know of have been in the controller unit, unless maybe one was with the air handler (can't quite remember that one).

-Chris

[ranger58sb]

Originally Posted by davechili

I have flushed and cleaned lines thru both units, and have replaced strainer filter. I also replaced lines between strainer and pump.
I think it is related to the compressor not telling the pump it wants water. As long as the front unit is requesting water, all is fine.
Does this make sense to ya'll ? Either trigger in pump relay,or wiring to relay seems logical culprit.

Yep, sounds like you've eliminated low water flow as a problem. I think you're saying the questionable unit actually does cool (compressor runs) when the pump is already flowing because of demand from form the other unit, yes?

If so, and in broad terms, makes sense.

I'd have to look at the controller schematic to know for sure which name to call which part

-Chris

[a64pilot]

My March pump went out two weeks ago this weekend.
From my olden days of having two units on the Sportfishing boats my most common problem was blocked strainer of course followed by the AC pump. The HVAC units were almost bullet proof until age and corrosion got them. No need to have a separate thru hull for each pump, or at least mine have never pulled air through the other pump when only one was running.
One pump serving more than one AC unit is done as a cost saving for the boat builder


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[ranger58sb]

Originally Posted by a64pilot

My March pump went out two weeks ago this weekend.

One pump serving more than one AC unit is done as a cost saving for the boat builder

Sure, but I can usually find something else that needs fixing right now, rather than fooling with something that works nicely at the moment. I don't expect a pump to last forever, in any case. I reckon this one will eventually tell me I've gotten my money's worth (12 years old now, I can't argue with that), and it'll be time to replace. At the risk of jinxing a project, that isn't too difficult in our installation.

-Chris

[jeremiason]

Originally Posted by a64pilot

I still don't understand why you guys with multiple AC' a tie them to a single point of failure.

Just had to replace one of my pumps.... My pump was 7.5 years old when it failed on me

The smallest pump available from Cruisair is 510 gph and will feed two AC Units.

$300 is my guess why people don't use multiple pumps, if they don't have too.