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Old 18-03-2011, 13:08   #1
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Marine Air Conditioning Problem

My boat has been sitting in San Diego since November. At that time the AC was working fine. We just returned and found that the AC wasn't cooling or heating.

I put gauges on the compressor and saw that I wasn't getting any compression. I thought that perhaps that I had a leak, so I vacuumed the system, but found that it held the vacuum overnight. I then recharged and once again saw that I wasn't getting any compression when cooling. I then ran some tests and am quite confused by what I'm seeing.

In cooling mode, I see the low pressure side reading decrease as expected, but I see no pressure increase on the high side. When I put it into reverse cycle heating mode, I see ~115 PSI on the suction side, but there is no pressure decrease on high side as measured at the rotolock valves on the compressor.

The compressor is clearly generating compression as shown by the heating cycle. I'm absolutely stumped as to why I see no changes in pressure at the high pressure rotolock valve. My guess was that somehow or another the condenser loop was clogged, but then you'd expect the pressure reading to be effected one way or the other by the suction side.

Any bright ideas?

Geoff
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Old 18-03-2011, 13:11   #2
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re: Marine Air Conditioning Problem

I've seen the valves get stuck in the middle when not cycled for long periods. Try cycling between cool and heat several times and see if that helps.
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Old 18-03-2011, 13:48   #3
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Re: Marine Air Conditioning Problem

Thanks for the suggestion, but I've tried that and it seems that the reversing valve is functioning as shown by it the vacuum line vacuuming when in cooling mode and pressurizing when in heating mode.

-- Geoff
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Old 18-03-2011, 13:53   #4
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Re: Marine Air Conditioning Problem

What about current draw when the compressor is running? Low starting amps and low running amps may indicate the compressor shaft has become seperated from the motor output. Not repairable btw
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Old 18-03-2011, 14:43   #5
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Re: Marine Air Conditioning Problem

It drawing about 10A, which is lower than normal, but the system is not fully charged. The real issue is that I see no pressure fluxuation on the high pressure line regardless of it being in cooling or heating mode. I don't see how this is possible.

-- Geoff
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Old 19-03-2011, 16:47   #6
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Re: Marine Air Conditioning Problem

I've been running some more experiments. I've closed the rotolock valves so the compressor is isolated and I'm only accessing the high lines to/from the condensers. I vacuum the system and then open either side, and I see no change on the opposing side.

At this point I'm guessing that the capillary valves are blocked. Is this a reasonable guess? If so, how would this have happened and can this be fixed? Other guesses?

-- Geoff
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Old 19-03-2011, 19:31   #7
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Re: Marine Air Conditioning Problem

How quickly are you expecting to see a change? Typical cap tubes are small, really small.
Other than that, What sort of compressor is it? Reciprocating? Scroll?
Does it sound normal when you turn it on?
does it shut down for low or hi pressure?
what sort of controls? rotary knob or electronic?
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Old 20-03-2011, 04:23   #8
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Re: Marine Air Conditioning Problem

Sounds like loss of compression.
If so, back pressure will be well higher than normal, and high side will be lower than normal. Amps will also be lower as the motor has less load.
Leaks and blockages in capillaries( or any problem causing reduced flow thru refrigerant control) will cause the opposite symptom - lower back pressure
A simple test is to close the suction line at the compressor and determine if it can pull and hold a vacuum. Simple if there is a valve. Less simple if you must cut/unsweat/unscrew the suction line and seal it.
Also as far as leak testing, pressurize and search with soapy bubbles etc. Perhaps, see if it holds pressure for some time. Preferably boost the pressure with dry nitrogen.. Leaks can be extremely small and will not show for some time. Using a vacuum is not a great idea. The pressure differential is not great, and if there is a leak it will suck in ambient air/moisture...
cheers
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Old 20-03-2011, 07:47   #9
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Re: Marine Air Conditioning Problem

The system is a Marine Air 16K BTU split system with a 12K air handler and a 4K air handler. The compressor sounds normal when starting/running, but on occasion I have noted a sound that reminds me of a pressure valve releasing when shutting the system down. It's not all of the time and I don't remember if it's when in heating or cooling mode.

When I run the test where I vacuum down the lines to/from the air handlers, I wait for several minutes and see no change on the side opposite of what I open up. I would expect to see something within that time frame. Is that not a valid assumption?

Since I see 115 PSI develop at the LP service valve when in heating mode, I believe that the compressor is working properly and that the reversing valve is functioning properly.

To me this feels like a blockage between the reversing valve and the HP service valve, which includes the condenser. This would explain why I see no pressure change at the HP valve when in either cooling or heating mode. However, I don't understand how that would occur. Likewise, whatever blocked the RV valve also effected the air handlers.

Am I just barking up the wrong tree or what?

-- Geoff
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Old 20-03-2011, 08:36   #10
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Re: Marine Air Conditioning Problem

Installing a prepackaged system do it yourself is one thing. Checking electrical components doable to some extent.
Troubleshooting the refrigerant side (heatpump especially) is quite another.
IMO it's time you get professional help. Even if you determine a stuck reversing valve of plugged cap tube what will you do about it?
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Old 20-03-2011, 09:15   #11
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Re: Marine Air Conditioning Problem

I just found out something that I didn't know…that the gauge ports on the Marine Air system have Schroeder valves. My refrigeration system doesn't have Schroeder valves. Anyhow, due to access restrictions, I had reversed the HP hose so that the end with the pin which depresses the Schroeder valve was at the gauge end! Duh…Won't make that mistake again.


Now it's back to taking some real readings and diagnosing this.
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Old 20-03-2011, 09:50   #12
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Re: Marine Air Conditioning Problem

Check the other fourm you posted on. I posted a diagram of a hp refer system that might give you an idea or the flow of freon in your system. All other info may not apply now that your readings are off.
Dwain
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Old 20-03-2011, 21:29   #13
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Re: Marine Air Conditioning Problem

Now that you got the hose the right way around, unblock the water hoses so that the condenser works again (wild guess but true in 99% of all cases) and enjoy cold air

Hoses are plugged with sea-scum. Take them off to clean them out and flush them with fresh water before putting the unit out of service for a long period.

cheers,
Nick.
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