Air Conditioning not keeping up

[dtcom]

We have a 1993 Mariner 330 with a single AC unit. The AC works and blows cool/cold air, but it takes forever to cool the boat. The forward cabin gets cooler than the salon, but after several hours on a hot day, the salon goes from around 90 to around 85. There seems to be enough air blowing, and the filter is clean.
Does anyone have any ideas? On a related note, is it OK to leave the air conditioning on 24/7?
Thanks!

[Midnightsun]

A Mariner 330 has a rather large interior and boats are not insulated at all so with one unit which I must assume is a 16,000 btu, it will definitely struggle in very hot and sunny conditions. Closing the blinds and using a sunshade on the front window will help quite a bit which is what we do when we leave the boat. We have always run our 24/7 however we do up the settings a bit when we leave the boat.

[g36]

I agree totally with what was mentioned about sun shade on the windows. Also you should be able to see a apx 15 degree or sometimes more temperature drop at the ac supply from room temperature. Have you placed a thermometer in the ac duct and measured how cold the air is? You can be low on refrigerant and still get cool air but not cold. Once it gets so low it will ice up. Did it used to do better?

[km1125]

It just takes a little bit of a buildup of growth in the cooling tubes to eat into the capacity of the unit. Have you flushed the cooling tubes with something like barnacle buster or something similar?

Just to give you an example, if the flow dropped from 8 gal/min to 6 gal/min (which still seems like a lot of water), that's a difference of almost 10,000 BTU every hour!!

Any type of obstructions in the water low will cut into that. Is the strainer CLEAN? Is the water pump impeller CLEAN?

And it is typically fine to run the A/C continuously, but you do need to make sure that there is air and water flow so the unit doesn't shut down (for something like a high pressure fault), so make sure the filters and strainers are clean before you leave the boat. You'll get an idea how often they need to be cleaned depending on the area the boat is in.

Also, make sure your shore power cords are in great condition. Leaving A/C running is one of the big reasons why shore power cords overheat, which typically happens right at the shore power inlet on the boat. The ends of the cord get corroded or dirty and cause high resistance and the A/C running will cause this area to heat up and eventually melt if they're not in good condition.

[bud37]

Just to add...you can shoot your inlet and outlet ductwork with an IR temp gun to get an idea if the unit is working as good as it can , but in my experience these boats are not insulated and when the heat and humidity is way up they are hard pressed to stay cool especially when the water around the boat is warmer as well and the surrounding deck is 115+ degrees.....take some checks of the deck and hull with your IR gun, it is an eye opener.

You may simply need an added small unit like many have done after you have exhausted all the checks.

Personally I have never liked leaving things running while away from the boat..( that would depend on your marina as well ).....far too many things can go wrong as KM suggested. In the news recently was a local boat that sank after a fire at night....no tellin what caused it but nevertheless.

[Viper]

Leaving an AC running while you're away for the week is an invitation for disaster IMO. Actually more than just opinion, can't say how many calls I've been on where extensive damage to flooring and cabinetry, and near sinkings have occurred due to major failures in the raw water circuit. It's no different than leaving your dockside water turned on while away yet most of us realize the dangers and shut them off. Aside from the safety concerns and stress on the electrical grid, consider too that this increases marina expenses which is just another justification to increase your slip fees. Marinas are also starting to monitor and penalize those that leave their units on while away from their boat. To each his own but it really isn't a good idea based on my experience.

[Cooler]

I agree. Besides, you will wear out the AC much faster by leaving it on. I had a similar issue with hot days. I bought one of those small cube type portable AC units. It really helps to keep the salon cool when running both. They are only around $40 USD, and are surprisingly effective. er

[km1125]

Viper''s points are all valid about leaving the A/C running when you're not there. However, I'm not sure that's what the OP intended in the question " is it OK to leave the air conditioning on 24/7". If you're at the boat and things are running correctly, there should be no issue running the A/C 24/7.

And, ideally, if you want the boat cool when you get there you should rig up some kind of remote and activate it when you're headed out that way. There were a couple threads on here about that.

[Midnightsun]

I would not compare 80+ psi dock water to a 1 psi circulation pump. Although anything is possible, springing a bad leak on an AC circulation line must be next to impossible if you ask me unless the boat is very old and the lines are rotted out.

[km1125]

Source of the post I would not compare 80+ psi dock water to a 1 psi circulation pump. Although anything is possible, springing a bad leak on an AC circulation line must be next to impossible if you ask me unless the boat is very old and the lines are rotted out.

I've never seen anywhere near 80PSI on dock water... maybe closer to 35-40 in most locations I've been in. The higher pressure though sure would test those parts of the system that were designed for it. But I'll bet if you look at insurance stats you'd see similar number of boats that were lost due to potable water system vs the HVAC cooling system water. However, good maintenance and regular inspections would reduce either issue to near zero.