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Old 02-02-2019, 04:33 PM   #1
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DIY Replacing of A/C?

On the good old scale of 1-10, 1 being even a caveman can do it, 10 being don't even think about it, how difficult of a job is it to replace an A/C unit? I currently have old Marine Air units. Beginning to show signs of age and I would rather replace them on my time table. The APPEARANCE is that there is not much to it. You pull one out and replace it with a new one. Wiring, circuit breaker, adequate water flow, etc. verified adequate of course. Is this just another deceptive trick played on me by my boat?
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Old 02-02-2019, 04:43 PM   #2
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Pretty easy! Most new units are smaller in size than the one you're taking out. Older units are almost always piston compressors, as opposed to the newer units that are rotary compressor. This means they generally use around a 1/3 less amps for the same BTUs, so 120 VAC wiring and breaker don't need to cchanged Thermostat or control will likely use a different wiring harness which may be a PIA to route. All in all, about as difficult as changing the water heater, hardest part is getting the old one out and the new one in.

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Old 02-02-2019, 04:48 PM   #3
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No there isn't much to it. Make sure you buy a unit with the same air discharge position. Most let you rotate the blower housing to any angle, but you want to be able to match the existing ductwork.



While you are at it you might also want to replace the r/w pump as these can fail over time. March is a good brand. Then you have to wire the A/C supply, hook up the r/w pump electrical and hook up the new thermostat. All straightforward.


David
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Old 02-02-2019, 04:51 PM   #4
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Thanks Ted. I think I would call in an A/C guy to check out the install afterwards. It seems I can buy two of the units for the price of one installed. Just seems big dollars for something that appears to be not so hard. I think I may have lucked out on the controls as they are located right next to and above the units. No fishing wires of any real length.
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Old 02-02-2019, 04:58 PM   #5
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One thing to pay special attention to is duct size. If the discharge on the old unit is 5" and the new unit is 6", don't step it down to 5" to utilize the ducting! Air flow and water flow are everything to a marine AC unit! Reducing duct size reduces airflow (CFM) over the evaporator which reduces efficiency and BTUs of cooling. I'm not saying it won't work, but do you really want to lose 10 to 20% of the units capacity. This also applies to raw water going through the condenser. Efficiency is all about getting all the heat out of the gas going through the condenser. Most manufacturers have their owner / installation manual online. Read it before buying to compare ductwork and water flow requirements to your current system.

Ted
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Old 02-02-2019, 05:00 PM   #6
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If you go MarineAir to the same, you can also reuse the control cable to the thermostat- mine was 20 years old and still compatible. The DTU units have fully rotatable blowers some of the others rotate, but only for 90 degree angles. If you call the dometic service department- Ive found them to be very helpful and spend time pre-sale
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Old 02-02-2019, 05:01 PM   #7
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Quote:
Originally Posted by djmarchand View Post
No there isn't much to it. Make sure you buy a unit with the same air discharge position. Most let you rotate the blower housing to any angle, but you want to be able to match the existing ductwork.



While you are at it you might also want to replace the r/w pump as these can fail over time. March is a good brand. Then you have to wire the A/C supply, hook up the r/w pump electrical and hook up the new thermostat. All straightforward.


David

Thanks David. Would seem to be a good time to replace the wiring. don't want to make work and I haven't inspected it closely but I'm betting original to the 1987 boat.

Had some maintenance done on all three a few months ago. All have good water flow and I flushed them at the end of last summer. Aft stateroom is holding charge and working fine on AC but very little heat coming out. Salon unit has a slow leak where it can't be easily fixed and no heat. The V berth unit has an issue. Something about one side losing pressure to the other and....no heat. I realize the no heat issues are most likely caused by the valve sticking from no use. Will try taping them with a mallet to see. However, with summer coming I need good salon and v berth units and those are the two I am looking at right now. Mostly the salon. Start with that one.
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Old 02-02-2019, 05:09 PM   #8
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Originally Posted by O C Diver View Post
One thing to pay special attention to is duct size. If the discharge on the old unit is 5" and the new unit is 6", don't step it down to 5" to utilize the ducting! Air flow and water flow are everything to a marine AC unit! Reducing duct size reduces airflow (CFM) over the evaporator which reduces efficiency and BTUs of cooling. I'm not saying it won't work, but do you really want to lose 10 to 20% of the units capacity. This also applies to raw water going through the condenser. Efficiency is all about getting all the heat out of the gas going through the condenser. Most manufacturers have their owner / installation manual online. Read it before buying to compare ductwork and water flow requirements to your current system.

Ted
Quote:
Originally Posted by Gmarr View Post
If you go MarineAir to the same, you can also reuse the control cable to the thermostat- mine was 20 years old and still compatible. The DTU units have fully rotatable blowers some of the others rotate, but only for 90 degree angles. If you call the dometic service department- Ive found them to be very helpful and spend time pre-sale
Yes, have my manual downloaded and will look at the ducts onboard. Again, lucky as the vents are located very close to the unit. Looking at Marine Air/Dometic and Webasto. Those seem to be the two standards although others are spoken well of. I have the old style I guess you call them analog controls, knobs.
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Old 02-02-2019, 05:19 PM   #9
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Here is the guy who helped me. I also posted his name a couple weeks ago and the other TFer got the same great service I did

Mark Bower
Service Technician

Phone (954) 366-2778
mark.bower@dometic.com

Dometic North America, 2000 N. Andrews Ave, 33069 Pompano Beach, FL
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Old 02-02-2019, 06:08 PM   #10
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They are really pretty simple to install especially since the through hull, pump, wiring and duct work are already there. Just check the condition of the duct work and see how well it was installed initially. You may find it crushed and tied so tight that it wont pass air properly. Now would be the time to fix it also. Check the condition of the water hoses too. You will love the newer units compared to the current ones. Good luck.
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Old 02-02-2019, 07:07 PM   #11
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Like Ted said - not very difficult. The hardest part for me was lifting the old unit out of the cabinet it was installed in. I did one in an afternoon. The drip pan drain connection did not line up and I had to modify the wood supports a bit.
The wiring connected straight up, along with the raw water. Use new hose clamps.
Good luck
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