How cold should our A.C. be able go?

[hillsideshortleg]

The other night we turned the A.C. down to 60 deg and it never got below 68 deg. This is a heat pump type A.C. unit. is it normal to not go down to 60 deg.? The water was around 70deg.
Thanks
Still new to the boat and learning.

 

[Ten Years Gone]

What was the outside air temperature/humidity/dew point? How many cubic feet of space where you trying to cool. How often were you opening companionway door or hatches/portlights?

And if I may ask another question...why would you want it to be 60 degrees? I don't know anyone who wants their house that cold! Much less the cramped quarters of a boat cabin.

 

[matthewmiller01]

How long did the unit run? I did this one night onboard and the inlet filter actually froze over due to low air flow and high humidity. The air flow (while we were sleeeping) went from great to almost none. I turned it off and let the ice melt off the filter (then cleaned it because I actually found it) and all was good again. If you have a large temperature drop to accomplish, you need to do it in steps to allow the unit to cycle off and on - especially if the humidity is high. If you don't, icing will happen as it did to me.

 

[mainstream]

The other night we turned the A.C. down to 60 deg and it never got below 68 deg. This is a heat pump type A.C. unit. is it normal to not go down to 60 deg.? The water was around 70deg.
Thanks
Still new to the boat and learning.

I routeinly keep mine at 64 on a 90'degree day with no problem. I can have my cabin at 80 turn it down to 64 with no problem. Problems occur when there is not enough water flow with high ambient sea water temp. A high sea water temP can cut capacity in half. Freezing occurs when low charge or not enough air across the evaporator. I would start with the ac sea strainer if there was no sign of freezing. Just my .02

 

[mistercomputerman]

It is 91 degrees here right now.

I have 53.9 degrees coming out of my salon unit vents and 52.2 degrees out of the forward cabin AC vent.

It is 72 degrees in the cabin and I have had the top half of the door open all day.

 

[jg300da]

It is 91 degrees here right now.

I have 53.9 degrees coming out of my salon unit vents and 52.2 degrees out of the forward cabin AC vent.

It is 72 degrees in the cabin and I have had the top half of the door open all day.

This.

You should not be interested in the temperature of the cabin as much as you should be in the "split".
That is the difference between the cabin (or return) temp and the discharge (supply) temp.
Typically a 18-22 degree split is ideal and indicates proper system performance.
Whether or not the unit can cool a cabin to a specific temperature is based on many factors, most of which has been addressed by Ten Years Gone, and none of which has anything to do with how low you set your cooling setpoint.

 

[mainstream]

The split you are talking about is the cross coil temp which is as you said difference between feed and return temp 18 to 20 is acceptable but you can get as much as 28 to 30. Your inside temp should be 20 to 25 degrees cooler then outside

 

[Xplicitlnck]

I'm a freak when comes to sleeping in the cold. I turn my AC down to 55 and let it run. I got my cabin down to 58 once and still had the fan on.

 

[MonacoMike]

Deleted... Misread post... MM

 

[hillsideshortleg]

Ten Years Gone
Have you ever heard the song "Cold Ethyl" By Alice Cooper? LOL . We just like it cold and have a hard time sleeping in warmer weather. The night we were up there I think it was probably around 68 deg and the cabin door was shut all night. I checked the flow of the water dumping out the side of the boat and it looked like full flow. It's a 280 SunDancer so there isnt a whole lot of room in there. I dont know what the dew point was or humidity. Dont these things go through a defrost cycle to keep them from freezing up? I left the manual in the boat so I havent been able to study up on it.
Thanks for all the advice
Rick

 

[Ten Years Gone]

Hi Rick,

Nope, haven't heard that Cooper song yet, but will Googal it shortly! :smt024
I am like you too in that I can't sleep if I'm hot, which to me means anything above 70. Where I draw the line is having to use blankets to be comfortable in the summer! :huh:

I don't even have on-board air, so I cannot speak from experience...only from the education I'm getting doing all of this research to purchase the best A/C unit for my 250DA. What the others alluded to is absolutely correct...a 20-25 degree split is ideal. Not only at the coil/evaporator on the unit, but between inside and outside temps as well. The same is true for a residence. Ask any reputable HVAC tech and they will tell you it is not good for the system, or the house itself to have wide splits during obnoxiously high temperature conditions. The reason humidity, dew point and (in our case) lake water temperature are so critical, makes for a compelling discussion; but I won't go into it here.

Suffice it to say, the number of required duty cycles to maintain a comfortable environment will have a pronounced effect on the useful life of the A/C unit components. That's why I questioned your attempt at such a low setting. The units are designed to be efficient at a certain duty cycle. These devices can be stressed past their design limits into premature failure. There is a reason why marine air manufacturers and home HVAC folks have system sizing recommendations. I know it isn't in keeping with the modern adage that "bigger is better", but having a system that is oversized is just as inefficient as undersized. Even though I know my home A/C is capable of running down the interior temp's to 70 degrees when it's 100 out...I don't do it. I set it for 80. I'm trying to avoid having to replace parts any earlier than necessary.

Since your outside air temp was around 68 degrees, I can't imagine why your system would not perform properly. Definitely sounds like a component failure to me, not system wide. When you have an opportunity to try it again, please PM me. I would be interested in knowing what you discovered, if anything, to learn more about the peculiarities of marine A/C systems that are in use.

Regards :smt001

 

[jg300da]

The split you are talking about is the cross coil temp which is as you said difference between feed and return temp 18 to 20 is acceptable but you can get as much as 28 to 30. Your inside temp should be 20 to 25 degrees cooler then outside

It doesn't work that way.
There is no amount of temperature difference that the cabin "should be".
A/C systems are not engineered that way. That is a function of the way systems are sized for a particular application, not a function of how they operate.
It is possible to have a split in excess of the 18-20 degrees mentioned, this is typically accomplished by lowering the load on the evaporator (cooling) coil by either a reduction of external heat load or lowering of the fan speed which lowers the internal load on the unit.
The 18-20 split is a number that should be achieved under maximum load conditions; fan on high speed and design ambient load conditions, typically 95 deg dry bulb outdoor temp. I'm not sure of the design criteria for entering seawater temp.

Something else to keep in mind, boat manufacturers do not make a different size unit for each model. My 2002 300DA used a 12,000 btu unit from the factory, as did the 320 and 340DA models of the same year. These three boats had much different interior volumes and as such would have different loads on the a/c unit resulting in different splits and different cabin temp/outdoor temp differentials.

 

[Four Suns]

It is 91 degrees here right now.

I have 53.9 degrees coming out of my salon unit vents and 52.2 degrees out of the forward cabin AC vent.

It is 72 degrees in the cabin and I have had the top half of the door open all day.

72 degrees my butt. Rick keeps his cabin like a freekin' meat locker. I got frost bite last time I was in there.

 

[Ten Years Gone]

There is no amount of temperature difference that the cabin "should be". A/C systems are not engineered that way. That is a function of the way systems are sized for a particular application, not a function of how they operate. Something else to keep in mind, boat manufacturers do not make a different size unit for each model. My 2002 300DA used a 12,000 btu unit from the factory, as did the 320 and 340DA models of the same year. These three boats had much different interior volumes and as such would have different loads on the a/c unit resulting in different splits and different cabin temp/outdoor temp differentials.

Ah, very good observation jg...as I recently discovered during my rounds with the different a/c mfr's. I have been quoted everything from the smallest unit available (6k btu) to the largest that would fit my space (11k) And the difference in price was only $250 to get that extra 5k of cooling. But what I'm learning about sizing and operational loads is exactly what you are prescribing above.

 

[dwna1a]

How cold? This is what the wife and kids say... Outside it was around 95 / 98 when we closed up for the night. When we got up in the morning there was a foot of snow on the cabin floor, frost covering the forward deck, and a half inch of ice surrounding the boat. I slept like a baby :thumbsup:

 

[Bucit]

Water temps are around 88deg here with very high humidity. I have my AC at 68deg and you can hang meat int he cabin. I usually turn it to 70deg when we sleep so I don't wake up with frostbite. Maybe the difference bewtween high heat/humidity and the dry colder air in the cabin feels much colder but I couldn't stand the cabin if it was 60deg?

 

[Southpaw II]

FWIW, water temp has a lot to do with how these units perform. Above 80 degrees, and it's hard to keep a boat cool, especially if you don't have a covered slip. Below 40 degrees and they struggle to put out heat. For guys that pull their boats in the winter, it's not a big deal. But, for those of us that keep their boats in all year, we see the extremes.

Don

 

[tomk]

I have an Issue with the inside cabin temp being about six degrees colder than the thermostast says it is !

 

[Ka1oxd]

The house AC quit Friday night when it was 96 degrees and 72% humidity. When the guy was here fixing the unit on Saturday (cannot wait to see the bill), a unit that is too big will not remove the humidity from the air. It will cycle too quick and not take the time to create the day air. Same with a unit that is too small, it will be working all the time, but dry the air out too far. What he stated was the best air conditioner works to keep the inside 20 to 25 degrees cooler and dryer than the outside air.

On the boat, the condenser unit I have to vacuum out frequently since the cooling vanes get filled with dust that reduces the air flow through the unit. Once a month I take the shop vac and clean. BTW the Admiral wants it so you can freeze ice cubes. She will crank the unit full all the time. I walk by and check that she does not set the coldness more than 3/4 of the dial. The boat gets cool and dry. I do need a service done, I want him to flush and refill the system to make sure it is working at the right limits.

 

[aquadancer]

I don't know anything about design limits but my boat will easily maintain 70 deg inside on a 95 deg humid day in full sunshine. Water temp is now in low-mid 80s and cabin door are frequently open.

I like my boat cool, dry and comfortable and my AC delivers so I guess Searay installed the right units.