Another A/C Problem

[rgtet]

I have a question on air conditioning and I'm seeking some ideas/guidance. For whatever reason, my air conditioning will pump water for a few hours, then cease pumping, at which point the pump motor casing will get extremely hot to the touch. It won't pump for a few days, then will magically restart. The intake and discharge appear to be fine, both at the entrance/exit to the boat as well as the pump itself. There's enough positive pressure from the pickup/seacock that I can remove the pump intake hose and water will flow (pumps haven't lost prime). I've also loosened the discharge hose clamps to bleed any air that may be on that side of the pump. I'm guessing that there isn't any hose blockages b/c the water will flowly correctly; from a visual check, the discharge stream appears "correct" on the occasions that it does work.

The same thing happens with my refrigerator. I replaced the refrigerator water pump this afternoon and the same thing happened.....it pumped for a few hours, then quit and the motor casing was extremely hot. The impeller on the old pump was completely intact, so I doubt that there are any stray pump pieces in the water lines. On this one, there is also enough positive head pressure from the pickup that the intake side of the pump has not lost prime.

At this point, I'm kinda stumped. The manuals don't get that deep into trouble shooting. I'm fairly mechanically inclined and have multiple engineering degrees, so I've eliminated all of the easy checks/problems and dumb operator error issues. Thanks in advance for any thoughts/ideas.

 

[Bill Roosa]

Are you on shore power for the AC (probably) and the reefer pump?
I'm thinking several things but before I get you excited I'd like to know more.
Does the raw water have lots of organic matter in it? Plants?
Do the motors turn or are they stalled?
If they are turning are turning faster, the same or slower speed or don't know?

 

[capshroud]

There are a couple of things I can think of. One, have you checked your water strainers that they are clear and not restricting flow and overloading the pump motors. Two, have you checked voltage? Low voltage will cause motors to overheat.

 

[Don S/V ILLusion]

Because of the commonality of two pumps having similar issues, my first thought is a voltage problem. Have you checked the voltage under load at both pumps? Also, are the two pumps made by March Company?

 

[woodster]

Also, are the two pumps made by March Company?

why do you ask Don...just asking is all i have a March pump that i will be useing some day.......

regards

woody

 

[Bill Roosa]

I'm thinking his shore power is having some issues like low voltage. That would make the motors run hot. It could also be a bad coil in the AC pump that once hot shorts and stalls the motor. Given that both (I think) are shore power and the reefer pump is new I'm leaning toward the shore power voltage being low

 

[rgtet]

Thanks for the responses. The strainers were cleaned on Friday. There was no obvious organic matter in the pump inlet lines (as I said, they both pumped for a while, then quit and the motors heated up; the A/C pump will restart after a few days of off/down time). The reefer pump is a March 12V DC pump; A/C pump is 120V AC (can't tell the manufacturer, the label/pump is rotated such that I can't read the flow rating or brand without removing the entire pump system). I did not check the voltage explicitly, but I didn't see anything odd on the panel gauges that would catch my eye (DC Panel is consistent at 13V DC, fed from the house battery, which is connected to the charger).

I dismantled both the old and new reefer pumps to check for an obvious difference in how well the impeller/stator turns. The impeller for the old pump had a bit more rotational friction than the new one, but nothing that would be obvious in terms of a problem- it still turned easily in when manipulated manually when partially disassembled. The old pump would not turn at all under power, so I couldn't tell you if there was a delta in the rotational speeds.

Another data point is that when I accessed the reefer compressor unit while connected to the old pump, the error light on it gives an flash sequence to indicate low battery voltage; also, as the compressor would try to cycle the pump on, it would cause a brownout in the 12V DC lighting. This was NOT happening with the new pump.

I guess a question becomes, what is the "right" sized pump for a reefer? Is it typical to have a 12V DC pump with a 3/8" discharge? Do the compressors require a higher flow rate to ensure sufficient cooling? Is it more appropriate to have a 120V AC pump on the reefer?

 

[Don S/V ILLusion]

Woody
The reason being these type pumps are prone to failure for a couple of design reasons discussed on an earlier thread. Among the problems encountered was one literally blowing apart from the heat and if the owner was not aboard, the boat might have been sunk. If it were me, as it was recently, I'd replace the M pumps with Cal pumps.

RGTET - "I did not check the voltage explicitly, but I didn't see anything odd on the panel gauges that would catch my eye". Not surprising as that would not indicate any problem at the pump(s). What I suggested was the verify you have proper voltage AT the pumps. My other comment above would obviously also apply but first things first...

 

[rgtet]

Don: I don't think I can check voltage at the pump, short of cutting off the butt connectors and heat shrink and twisting the wires together in order to measure voltage under load. The wires to the pump are from the compressor unit, so I might be able to measure voltage at the compressor. This would ultimately track back to a problem at the compressor and not at the pump itself.

With regards to the Cal pumps, are these AC or DC? A quick check of their website led me to believe that the marine pumps that they have are AC. I'm assuming that you replaced a different vendor's pump with a Cal pump....

 

[Benny17441]

No, your reffer pump should be 12V so that you can run it when underway. Since the A/C requires AC current anyways it is just logical to run a 120V pump. There should not be a connection other than coincidence between the overheating of the 12V pump which runs off the batteries and the overheating of the 120V pump which runs off shorepower. Like Don indicates you need to test the actual voltages at the pumps. It may be that the brand of pumps being used are not very tolerant of low voltages.

 

[kenny]

reefer pump

Are you on shore power for the AC (probably) and the reefer pump?
I'm thinking several things but before I get you excited I'd like to know more.
Does the raw water have lots of organic matter in it? Plants?
Do the motors turn or are they stalled?
If they are turning are turning faster, the same or slower speed or don't know?

I had the very same pump problems plus the hum noise at night. I changed the compressor to a fan cooled no more water cooled . can not hear the hum and it is more eff. works great. I have a 410 KEN

 

[rgtet]

An update to my pump problems.....

The reefer pump was working today when I turned the system on. I subsequently bled a small amount of air out of the system, re-tightened all of the fittings/hose clamps, and put power to the reefer a second time. It sounded like there was a minute amount of cavitation coming from the impeller and there was a tiny amount of bubbles visible in the pump discharge hose. I checked the strainer and it appeared that there was a small amount of bubbles in the strainer (localized to the top 1/4" of the clear cup, just below the discharge outlet). Is it possible that the pump is pushing more water than the pickup can provide? This seems highly doubtful, but I am curious why a previously full strainer would show those air bubbles (I verified full pipe flow by loosening the pump inlet hose clamps and burping out the last bit of air under static head pressure from the pickup). It ran and pumped water (good overboard discharge), but the pump body was a bit warm after 5 minutes; is this normal or does the water flow cool the pump body?

The A/C pump was a different story. It is still down hard. I stripped the pump down to ensure that there was no foreign objects or organic/animal matter in the inlet lines and pump fittings. The impeller was completely intact and rotated fairly smoothly (some resistance, but not "too much"). Should the pump have any resistance when the impeller is turned manually or should it be completely effortless? I put the pump back together, bled air out via the pump discharge hose (under static head pressure), then tried to restart the A/C system. Upon startup, there were a few clicks from the compressor unit/relays (I assume that one of them is the attempt to command the pump motor on); the pump did NOT start, but the fan motor did start pushing air. My guess is that the pump motor just happened to reach the end of its life and it is time to be replaced. The pump is a Little Giant model. Is there something better to use or is this an acceptable model for a 16k BTU MarineAir system? There have been absolutely no problems with the A/C system until now. Is there anything to check on the compressor unit to ensure that it is functioning correctly and/or is sending the correct command signals to the pump motor?

 

[Benny17441]

There should be no resistance except a magnetic pulse as the Armature turns past the Field. You mention you had the pump apart, it would have been a good time to bench test the pump motor with a separate power source. It is necessary to get a reading on the voltage at the pump motor as it will be an indication wether the problem lies with the motor or the upstream wiring or components. Be careful when working with 120V power; shut off shore power and disconect your cable from the boat so no well intentioned passer by could turn the power back on.

 

[Bill Roosa]

What chu gots there with you reefer pump rgtet is a head grimlin. If you have air bubbles in the strainer then it HAS to be above the free water surface. Otherwise it would be leaking water out and not suckiing air in. That makes me think that, since the pump is further down stream it too is above the free water surface and is loosing prime. Pretty easy to test, take the discharge off the pump and see if water flows with the pump off. it should. Centrifical pumps are really bad at priming themselves when above the free water surface. which is why the instruction manual says to mount it below the free water surface to insre it stays primed. Also important is the actual route of the hoses. if the raw water inlet hose goes up above the free water surface before getting to the pump it will act like a syphon break when the pump stoppes and form an air picket which the pump may or may not be able to overcome. Kinda depends on the size of the air pocket trapped in the hose.

If you are getting brown outs from either pump something is major wrong. The reefer pump should only be drawing 1ish amps

 

[Benny17441]

I was also wondering about those air bubbles and I think Bill may have a good explanation for them. When you open the strainer with the through the hull valve open you should have water pouring into the boat. Have you relocated anything or perhaps moved or raise the intake hose to the A/C unit?

 

[rgtet]

The strainer is below the waterline. If the strainer cup is loosened, water flows quite freely from it into the bilge. The same happens at the pump, which is only about 1-2 inches above the strainer inlet/discharge. I'm wondering if there are/were still some air pockets in the hoses that were not completely purged.

The 12V lighting brownout was before I replaced the reefer pump. It leads me to believe that the problem was in the old pump windings.

 

[Bill Roosa]

OK, so how does air enter a system like that? That was retorical. Does the hose rise above the free water leve at any point?
Air pockets are a huge pain when initally installing these pumps.

 

[rgtet]

The air is in the system from when the strainer cup was removed and/or hose clamps loosened. When the system is put back together and the seacock opened, the strainer slowly fills with water. The more slowly that it fills, the more airtight that the system is (below the waterline). I tried to alleviate this by loosening the discharge side of the pump so that some water flowed out. This also gives air an outlet, since the water is incompressible and has to go somewhere to be fully purged from the system (water will fill to the point that the static head pressure is equal to the pressure of the air bubbles contained in the system).

I'm going to guess that the piping rises above the water line in the vicinity of the compressor unit, but can't be positive until I make some measurements from a common reference point to ascertain the elevations. I'm thinking that I might replumb the system in the off-season to put the pump close to the strainer to ensure that no part of it is above the waterline.....it also gives me new hoses and fittings throughout the systems.

At this point, I'm not too worried about the new reefer pump; I think that it's just an issue of ensuring that the pump inlet is below the waterline and continuing to bleed those last little bits of air from the line every time that I open/clean the strainer mesh and cup. I am still curious about the "right" operating temp of the pump body.