AC Systems behaving badly

[formosa64]

Hi all,

I have three cruiseair split systems on my 48 CPMY II. I came to the boat today and it was hot, well over 100 degrees inside and all three units were running showing displays with 100+ degrees. No water was pumping out of the AC raw water discharge and the pump was running. It was so hot that the glue on my mirrors separated and the plastic mirrors warped.

First of all, I would have thought my units would shut down if they weren't getting raw water - but obviously that didn't happen. I checked and all three are programmed to shut down on a fault. None of the units were in a fault condition, just not cooling whatsoever.

Turns out my intake screen was blocked, likely with cut grass.

Now both stateroom units have returned to cooling, the salon unit now just blows hot air. I may have finally fried it.

My questions then get into - has anyone put a flow detector on the raw water pump and relayed a shutdown for the power to the units? Seems like a good idea as the units just sit there and cycle on and off forever and this must be a way to burn up/shorten the life of the raw water pump.

Why don't these units fault when no raw water is present?

Why does a unit stop cooling if it's been running without raw water and then the cooling water resumes. What gets fried running it without cooling water?

The great mysteries of old marine AC continue ...

Thanks for all the info -

[Reefgeorge]

When the cooling water stops, or there is any major reduction in the heat exchanger process then the high side pressure starts climbing and when it goes over the limit of the high pressure switch, the unit should shut down . On the electronic controls like SMXII after a few cycles, the system goes into a fault condition and shuts down with a flashing display. With less sophisticated controls but with a high pressure switch then the compressor will shut down but the air handler will blow hot air. With no high pressure switch or one that malfunctions then the compressor runs until it overheats and then shuts down when the temp sensor on the compressor opens. Each time the temp sensor cools, the compressor does this cycle ad nauseum. If the system repeatedly overheated then the compressor may have seized. If so then with a call for cooling you will here the compressor try to start for about two seconds then quit due to high temp and then try again in about ten minutes. The confirmation is an amp probe on the hot compressor power wire and seeing locked rotor amps instead of normal amp draw when it tries to start.

Of course there may be a different issue that is unrelated or brought on by excessive heat like a start relay or capacitor.

George

[GJH]

Sounds like a pump relay is bad. Can happen with age, I replaced a few on my boat.

[Pascal]

If the compressor was fried the breaker would trip right away. Usually...

It sounds to me that someone either modified or messed up the installation. With no water flow your controls should have shown A high pressure error. When you say "all theee units were running" I assume you mean the air handlers not the compressors. Compressors have temperature protections so if they are forced to run without water, the high pressure switch doesn't trip the thermal protection will

You don't need flow switch. You just need to make sure you have a pump relay box so the pump only comes on when needed and shuts down if the intake gets clogged. And make sure the high and low pressure switches are properly connected

Try... resetting the breaker. if the compressor tries starting and/or runs for a while then gets hot

When is the last time the system was descaled? You could also have a blockage in the line going to that compressor. It s happened to me before and since it usually all goes in the same sea chest you can't tell until you pull that hose at the sea chest and check for flow

[Briankinley2004]

The original post and the thought of pumping my boat full of water are two reasons I leave my a/c off when I am not on the boat. That and my land lord gives a good cussing cause he is paying the electric bill. I run fans for circulation and plan to do like some of the other boats and get a residential dehumidifier although I havent had any mold issues with fans thus far.

[formosa64]

When the cooling water stops, or there is any major reduction in the heat exchanger process then the high side pressure starts climbing and when it goes over the limit of the high pressure switch, the unit should shut down . On the electronic controls like SMXII after a few cycles, the system goes into a fault condition and shuts down with a flashing display. With less sophisticated controls but with a high pressure switch then the compressor will shut down but the air handler will blow hot air. With no high pressure switch or one that malfunctions then the compressor runs until it overheats and then shuts down when the temp sensor on the compressor opens. Each time the temp sensor cools, the compressor does this cycle ad nauseum. If the system repeatedly overheated then the compressor may have seized. If so then with a call for cooling you will here the compressor try to start for about two seconds then quit due to high temp and then try again in about ten minutes. The confirmation is an amp probe on the hot compressor power wire and seeing locked rotor amps instead of normal amp draw when it tries to start.

Of course there may be a different issue that is unrelated or brought on by excessive heat like a start relay or capacitor.

George

The issue was that the systems were not showing any faults on the displays, just the temp, and the power lights and AC leds were lit and all blowing hot air. I have passport I/O and passport II's. Going down into the ER, one or two of the systems were cycling --- but the raw water pump was just running continuously. Probably been doing this for days.

So, it looks like there is a problem that the systems are not signalling the fault - which would then shut down until cleared. If all three faulted and shut down - then there would be no signal to relay turn on the raw water pump.

[formosa64]

If the compressor was fried the breaker would trip right away. Usually...

It sounds to me that someone either modified or messed up the installation. With no water flow your controls should have shown A high pressure error. When you say "all theee units were running" I assume you mean the air handlers not the compressors. Compressors have temperature protections so if they are forced to run without water, the high pressure switch doesn't trip the thermal protection will

You don't need flow switch. You just need to make sure you have a pump relay box so the pump only comes on when needed and shuts down if the intake gets clogged. And make sure the high and low pressure switches are properly connected

Try... resetting the breaker. if the compressor tries starting and/or runs for a while then gets hot

When is the last time the system was descaled? You could also have a blockage in the line going to that compressor. It s happened to me before and since it usually all goes in the same sea chest you can't tell until you pull that hose at the sea chest and check for flow

Yes, you are right- I mean the air handlers were running, the compressors (if that's what I was hearing in the ER) seemed to be cycling. I have no idea on the descaling.

I'd like to get the systems so they fault - shut down - and then let me address the problem. I mentioned that the programming setting on the displays were to shut down after a fault. But no faults were appearing.

[formosa64]

Yes, you are right- I mean the air handlers were running, the compressors (if that's what I was hearing in the ER) seemed to be cycling. I have no idea on the descaling.

I'd like to get the systems so they fault - shut down - and then let me address the problem. I mentioned that the programming setting on the displays were to shut down after a fault. But no faults were appearing.

How can you tell the compressor is "on" besides the "sound"? Thanks.

[formosa64]

If the compressor was fried the breaker would trip right away. Usually...

It sounds to me that someone either modified or messed up the installation. With no water flow your controls should have shown A high pressure error. When you say "all theee units were running" I assume you mean the air handlers not the compressors. Compressors have temperature protections so if they are forced to run without water, the high pressure switch doesn't trip the thermal protection will

You don't need flow switch. You just need to make sure you have a pump relay box so the pump only comes on when needed and shuts down if the intake gets clogged. And make sure the high and low pressure switches are properly connected

Try... resetting the breaker. if the compressor tries starting and/or runs for a while then gets hot

When is the last time the system was descaled? You could also have a blockage in the line going to that compressor. It s happened to me before and since it usually all goes in the same sea chest you can't tell until you pull that hose at the sea chest and check for flow

Yes, it sounds like you maybe right - the install is not proper - as the fault never appears on the display. The pump has always only come on when needed - but as the units were "cycling" (my impression) the pump was signaled to keep running.

[Reefgeorge]

How can you tell the compressor is "on" besides the "sound"? Thanks.

A clamping amp probe on the compressor hot lead. Volt meter on the same lead.

Hand on top of the can when it starts.

Someone watch the ammeter on the main electric panel when it tries to start.

George