Air Conditioning pump cuts out

[Jeff Bacon]

Hi All:

Recently, while running my Air Conditioner (heater, too), the circulating pump will do one of three things :
1. Run perfectly for hours on end
2. Stop circulating while the fan stays on
3. Pop the main circuit breaker

The intermittent nature of the problem, as well as the different result of whatever problem I have is driving me nuts.

Things I have checked so far:
- Intake strainer is clean and not blocked
- Plenty of water being pumped through system right up until it quits
- No restrictions around air intakes or exits
- Electrical connections are tight
- No changes have been made to the system
- Stopping and restarting when the problem occurs sometime fixes the problem, sometimes not.

This is a Marine Air 16,500btu system on a 2003 Hunter 386

I really have no intimate knowledge of how the system works, and any help pointing me to a starting point would be appreciated.

Thanks..... Jeff

 

[Rich Stidger]

You may have checked this condition, but is it possible that the A/C has frozen and blocked the water flow in the heat mode? This would stop the water flow while the fan stays on and perhaps it could cause the CB to trip. My Marine Air 16.5KBtu has frozen numerous times but has never tripped a CB.

An error code is set but only after a few minutes of no-water conditions.

If your problem occurs when cooling, I have no specific suggestion.

 

[Jeff Bacon]

Thanks Rich;

The problem does occur in both cool and heat modes. Also, the problem will occassionaly occur shortly after the unit is turned on before freezing can occur.

Still stumped...... thanks again

 

[Ray Bowles]

Have you checked the electrical (amp) draw of the pump? Is the pump body (motor end) real hot when it shuts down?
I had a similar problem that ended up being the pump. The electrical draw changed with different temps due to the weather and the amount of cooling required in the cabin. The end result was always a shut down of the cooling pump and followed by the AC shuting down. Additionally I found the filter that screened dust prior to air flowing through AC chilling radiator was very dirty and plugged almost totally causing the unit to run much longer than normal. The filter was in such a forbidden location that I never saw it for a long time.
Ray

 

[kloudie1]

Jeff, if it is a March pump, the little heat exchanger tube that cools the coil may be plugged. I just had the same symptoms and cleaning out the tube made the problem go away. Take the pump out and carefully disassemble and clean out the wet end . Don’t misplace the thrust washer! Take some limber wire like 10 gauge and use that to rod out the exchanger. I found some significant mud/organics in mine.. I could make it run after a trip by putting ice on the epoxy coated motor coil. The little copper tubes take a slipstream off the pump and cool the maroon colored motor coil. The little white "stick" is the shaft that the impeller and magnet spin on. It is ceramic and can be broken.. Carefully clean all the parts and re-assemble, pay lots of attention to the little seals that seal to the motor cooling coils.

 

[ChuckThomas]

does your head use the same through hull for input? mine does and when the rubber gasket in the head pump gets old it will suck air and do as you described.

 

[Bill Roosa]

failed coil in the motor

It is a little known fact that if an AC current motor is started with a bad coil (shorted) it will run fine due to the back electromotive force (EMF) caused by the rotors rotation. That is until the motor stops in just the right location and the start up coil is the shorted one. Not rotation happens and no back EMF so the CB pops
Take the unit appart and test for a ground or short on each coil

the main clew is the popping CB. Marine motors are designed to not overheat even when stalled. So they should never pop a CB unless there is a short somewhere. Course the short could also be in the wiring from the CB to the motor but I assume you checked that already.

 

[kloudie1]

OK need more info.. The standard pump with a Marine Air unit is a March LC-3CP-MD. Is that the pump you have? It also may be named P-500 on its case. Disregard my notes if you don’t have this pump.
When the water circulation stops, does the pump motor continue to run ? If yes, then it is sucking air from somewhere and losing prime (these aren’t self priming) .. If the pump stops and feels really warm to the touch, then the cooling tube in the pump motor may be fouled or the electric coil itself in the pump housing may be bad and going “open” when it heats up. The thermal trip in the coil could be going bad also. Next time the circulation stops, turn off the breaker before it trips. Then take some ice and put on the motor coil housing to cool it off.. After a couple of minutes of cooling, turn the breaker back on and start the AC.. If the water pump starts and runs a while, it is probably the motor cooling tubing that is plugged..If cleaning the motor tubing doesn’t fix it, then it is a bad electric coil or a bad thermal breaker inside the motor coil; both will require a new pump.. About every 6 years, my motor cooling tube plugs enough to trip the internal thermal breaker and stop the pump until it cools off and the breaker re-sets itself.
When the water stops flowing, the discharge pressure of the AC compressor rises and makes the compressor work much harder, which then trips the boat circuit breaker. One more thing to check is that the cabin air filter on the inlet side of the air conditioner unit is not plugged. That usually will not stop water circulation, but it can work the compressor harder and trip the breaker, which will stop water circulation. If you aren’t comfortable with this troubleshooting, get a gear headed friend to help locate the pump and do the troubleshooting and disassembly and cleaning with you.. He’ll work for the beers you promise after the AC is running again!..
Have Fun, Jeff