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Old 22-08-2016, 07:51   #1
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Air conditioning help please

I have 3 Dometic type 410 compressors.......2 work very well but the 3rd does not.......the compressors comes on but does not cycle on and off, so it freezes the coils and stops making cool air as nothing can blow through the ice.

I had someone come and look and he added gas which really did not change anything.....another guy came and said you have the new 410 model which not only need a new special gas but a certain weighted amount.....sounded knowledgeable but still the same problem

Any ideas or suggestions would be much appreciated
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Old 22-08-2016, 08:03   #2
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Re: Air conditioning help please

What temperature are you setting the thermostat, and is the ducting sufficient to allow enough air flow?

Is this a new installation?

are the air filters clean?

what size air conditioner (BTU)?
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Old 22-08-2016, 08:09   #3
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Re: Air conditioning help please

Sound like you may have an air flow issue. If the supply air is restricted, or the venting ( discharge) is restricted, or the blower speed is too slow, the heat is not transferred to the coils resulting in ice. One other possibility is that the unit is sucking in its own cool discharge air.

How many vents? How's the flow, clean filter and coils? Vent secure to unit and not leaking?

Hope this helps
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Old 22-08-2016, 08:22   #4
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Re: Air conditioning help please

Good suggestions to check thanks
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Old 22-08-2016, 08:45   #5
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Re: Air conditioning help please

It would have been appropriate to check the airflow first before adding refrigerant. Low refrigerant can also cause the coils to ice up but since adding refrigerant did not help, the unit may now be overcharged, or, if they didn't add enough it may still be undercharged. Hard to tell without putting on a set of gauges.

If you don't find a problem with airflow, you may want to have the charge evacuated, vacuumed and a new charge weighed in. Get the charge weight from the manufacturer. A good tech will always use a scale for this. Once you have checked airflow thoroughly, you can run the unit , once defrosted, and check if there is condensation on the compressor. A cool compressor with condensation on May be a sign of an overcharged system as is high amp draw.

Also make sure your fan is on high speed, on residential systems the discharge air should be about 10 deg f below ambient. IIRC
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Old 22-08-2016, 09:22   #6
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Re: Air conditioning help please

Dont know about air con but when that happens to a refrigeration unit its usually the tx valve freezing, and the problem is water in the system and that means faulty drier. I have no knowledge of air conditioning and I'm assuming its the same kind of system so I could be way off.
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Old 22-08-2016, 09:29   #7
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Re: Air conditioning help please

Issue I run into is most of the newer systems are sealed, You would have to add valves somehow or another to put gauges on it.
However not having valves really seems to help as I guess valves are often the leak sources
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Old 23-08-2016, 07:43   #8
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Re: Air conditioning help please

Many AC problems are solved by back flushing the system and using a de-scaling solution to clean up the water passages.
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Old 23-08-2016, 09:09   #9
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Re: Air conditioning help please

All good suggestions. Icing up also occurs if the a/c unit is not sized to the space to be cooled. Too big or too small can cause the unit to ice up. Also check the thermostat.
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Old 23-08-2016, 09:53   #10
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Re: Air conditioning help please

Maybe also check your relays. You said that the compressor is not clicking on/off as it should, it is not cycling and that could contribute to your problems.
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Old 23-08-2016, 10:07   #11
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Re: Air conditioning help please

Great suggestions, but you really need to go back to the beginning. Only a very few things can cause freezing. Mostly its Air Flow or Refrigerant. Refrigerant is the easiest to check. And by the way, if it's overcharged, it will run hotter not colder. Boyle's Law: Temperature of a gas is relevant to its pressure and the other way around.Also, if it's a split system, you can not weigh in the refrigerant due to varying lengths of the refrigerant lines to the evaporated coils. Simply set the super heat with accurate gauges and temp sensor. We use digital gauges for accuracy. On self contained units, you can weigh in the refrigerant. If this is a Dometic unit with R-410a, it is likely self contained. I find it hard to believe a tech would charge with the wrong refrigerant. If it's R-410, there's a round pink sticker right there on the compressor saying so. Also, the pressures are extremely different for R-410a and other refrigerants. Refrigerants can not be mixed. Superheat is different for different refrigerants. Some of the new refrigerants are blends, but there is a specific PT chart for that refrigerant. If someone mixes them, there is no chart for that mixture.

There are several possibilities for air flow problems:

1. Dirty coils
2. Upgrading the unit BTU capacity without upgrading or having sufficient duct size.
3. Dirty return air filter.
4. Insufficient return air.
If the problem is air flow, one of the above four should correct it.


I would be glad to assist you on the phone if you still have problems.
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Old 23-08-2016, 11:55   #12
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Re: Air conditioning help please

Some good advice above; when troubleshooting AC units on boats think:

E (Electricity, are you getting adequate voltage?)
A (Do you have good return AND discharge airflow) (a 16,000 needs 140sq in of return and unrestricted discharge
W (do you have good water flow? Measure discharge with how long it takes to fill a 5g bucket and verify with manual); clean the condenser (see manual)
R (if none of that works have a certified tech check the refrigerant
level but that's rarely the case on a small sealed unit

Good luck
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Old 23-08-2016, 12:37   #13
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Re: Air conditioning help please

I had an older 12,000 BTU Mermaid unit that kept freezing up. Had an air conditioner repair person look at it. Turned out to be the expansion valve. It had a tiny pin hole in and all the gas leaked out (I believe that AC guy said it was filled with nitrogen, but I'm not 100% sure about that).

He had to braze a new expansion valve assembly on to the AC unit. We removed the unit from the boat and he took it back to his shop. I think the repair ending up costing three hundred dollars or so. Not cheap, but this fixed the problem of the unit constantly freezing up.

A new 12,000 BTU unit was fairly expensive to replace so this repair was mostly worth it (especially since it's still working a few years later). If its a smaller unit, and this is the problem, you might be better off getting a new unit depending on the age of the unit that is not working correctly.

I hope this helps
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Old 23-08-2016, 22:31   #14
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Re: Air conditioning help please

Cooling system has proficiency in line. You can locate it at the conection with the bulge in the metal line. Takes a special tool to remove. Checking head pressure with manifold gauges will confirmed it. If it is restricted the line will ice over in a few min units from the oriffice valve back
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Old 27-08-2016, 19:11   #15
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Re: Air conditioning help please

Did you get the problem fixed?
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