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Old 08-23-2015, 04:41 PM   #1
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Default Problem with AC units

A problem has developed in my two Pompanette marine air conditioning units which is baffling me, and I hope someone with more knowledge will be able to suggest a remedy.
I will give a background as concisely as I can:
I have two identical 16,000 Btu marine AC units, one forward and one aft, fed by a single 120 volt water pump which splits to each unit. These units have run perfectly for three years. The water pump was submerged in a recent fresh water flooding, but I dried it out thoroughly, and it seems to pump as normal, and the flow through both outlets looks to be the same as it was before the submersion.
Afterwards both units ran as normal for about a month.
The recent problem:
The rear AC unit still works perfectly. But when I switch the forward unit on during the day it cools for about ten minutes, as I watch the voltage on my AC meter slowly rising, from a normal of about 11 amps, until it reaches 20 amps, then trips the 20 amps breaker, shutting down both units. Sometimes the forward unit just shuts down itself with a HPF reading, (high pressure fault), even before the rising amperage trips the breaker.
I then have to use only the rear unit, which is just keeping me sane, when itís over 100F outside.
In the evening, (when the temperature in Florida is considerably less than during the day), both units run all night, the forward one only clicking the breaker as the ambient temperature rises in the morning.
Clogged condenser fins will restrict air flow and cause a HPF fault, but I have cleaned them with both compressed air and vacuum, and they donít look any different to the aft unit fins.
The manufacturers told me a HPF fault is only caused by either a lack of water flow, or a reduced air flow. They cannot suggest why the amperage rises before it trips the breaker. Itís no good sending the unit back for inspection because they canít refill it with R22, because the law has changed and they now use different freon.
One remedy would be to find a marine AC engineer, but being a cheapjack yachty I thought I would ask here and see if I can fix it myself.
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Old 08-25-2015, 04:25 PM   #2
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excessive amp draw is usually a sign of compressor failure. since your other AC unit is functioning, it sounds as though your water pump (which should not be submerged0 actually survived its dunking. there are 2 amp draws when your AC unit is functioning-- one current to the blower/fan and the other to the compressor itself. good amp draw to fan/blower is usually 1 or 2 amps and most of the current is compressor draw, normally 10-12 amps. a bad compressor will draw excessive amps till it puts the unit into thermal shutdown --usually around 20 amps. ou can verify that it's a and compressor by putting n AC clamp amp meter on the hot lead to your compressor and r reading amps until the unit goes into HPF. can pull your compressor and take it for test by a local AC shop? bad compressor classic failure symptom is high amp draw leading to system shutdown. NB we have seen compressors which have copper tubing developing pinhole leaks-- if you need to recharge , this may be another problem. old systems can be purged of now-illegal freon, then recharged . maybe a local AC tech would try this for you instead of your buying a whole new compressor unit. ?
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Old 08-26-2015, 07:01 AM   #3
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Just spoke to my brother, who is a second generation refrigeration engineer with 40 years of experience.

Firstly, if the faulty unit has lost some gas, the evaporator could be freezing which will cause a Low Pressure Fault and increase in current draw due to restricted pipes. Since you have a HPF this one is unlikely.

Secondly - and more likely - a contaminant in the water line has partially blocked the cooling water through the condenser, causing the compressor to overwork in an effort to remove the heat.

Finally, a third possibility which I thought of myself (I'm an electronics tech) is that the run capacitor is leaky, causing the current to increase over time. However that possibility doesn't take into account the HPF.

So, it's almost certainly #2 above. Check and flush your water lines.
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Old 08-26-2015, 09:03 PM   #4
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Thank you both for these possibilities.
I won't be back on my boat for about two weeks but I'll do these tests and let you know.
I must confess, I have never "cleaned out" my water pipes in four years of intermittent use, so it's possible there is a restriction, causing the pump to overwork, even though it looks like the water outlet is as good as it has always been.
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Old 08-26-2015, 09:04 PM   #5
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A second thought along these lines:
Why does the forward unit run fine all night, then break down in the daylight?
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Old 08-27-2015, 02:10 AM   #6
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Yeah, I missed that little detail.

Best advice I can give comes from "The Art of War" by Sun Tzu - divide and conquer. Just keep breaking the thing down into smaller units until you find the cause. It worked for me my whole life as a computer engineer.
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