New AC, New pump, and MORE FROST!

[TWedd]

Frosting is caused by low evaporator coil temp. This will not be caused by the pump in cooling mode. Three possible problems:
1 Low on refrigerant. too much refrigerant will not cause frosting. New unit so this is the least likely cause, but still possible.
2 Low air flow- most likely cause. do every thing you can to remove restrictions from the air flow, the fan on these units do not like inlet airflow resrictions at all so remove as many restrictions as possible. checking the supply ductwork also is a good idea, however the fan can push more thru the supply duct than they can pull thru the return.Dirty air filters are the most common cause of frosting but not the issue on this new install. check with the MFG to see if your supply duct work is within limits.
3 Low entering air temp. once the entering air get below 70* the unit will be more likely to start frosting. check the temp of the entering air when frosting. if it is below 70* adjust the thermostat to cycle the unit off before it reaches that temp( 70* is a bit conservative, 68* is the lowest you should see, but that is pushing it)

 

[Redhook98]

When I upgraded all of mine, I had air flow issues on all of them. I had to put in more supply and outlet ducting to make them work right. One of them had great supply air, but the outlet was a miselry 4x6 vent only. That was for a 16000BTU system. Disaster.


One the plus side, the more ducting, the more efficient and the quieter the air flow.

 

[TWedd]

One frosting cause can be an overfill of the refrigerant.

I am not aware of any way overcharge of refrigerant can cause frosting. under charge yes.

 

[HiDHo]

The supply ducting looks OE and should be good, but you need an unrestricted return air flow to the unit. My 16,000 btu unit has a 12” x 12” return air grill one foot from the evaporator coil. Your frosting is caused by restricted air flow.
what size unit was replaced?

 

[toocoys]

I took out an 8k Dometic air from 1972 and installed an 18k.

 

[TWedd]

I took out an 8k Dometic air from 1972 and installed an 18k.

You will need to modify the duct work. Also open up the return air path, wide open. You need better airflow. Did you use the existing wiring also?

 

[toocoys]

You will need to modify the duct work. Also open up the return air path, wide open. You need better airflow. Did you use the existing wiring also?

I’d prefer not to rebuild my boat. If it comes down to it I’m going to switch ac positions and out this flagship in the front which will allow it ample intake as the grill will be right in front of the fins.

And yes I used existing wire because it worked.

I have an email in to steve at flagship. I’ll wait to hear from him before I start tearing things up again.

 

[TWedd]

Good idea. Found this on their website. you will need to install it as they require to obtain proper operation. Good luck!
FM18RLP
BTUs of cooling: 18,000
4″ discharge grills recommended: 4
Blower CFM (Cubic ft./min.): 555
KW of elec. Heat: 2
Amps (cool) 115/230: 12.9/6.1
Amps (heat) 115/230: 18.1/9.0
Length in inches/mm: 24/610
Width in inches/mm: 17/432
Height in inches/mm: 10.5/267
Wgt lbs/kg: 113/52
Designed for Catamarans which require low vertical dimensions.
View PDF

 

[Comodave]

I have installed Mermaid A/Cs in 4 different boats. They have specs on how many and how far the discharge vents have to be. Since you replaced an 8K with an 18K you may need to upgrade your discharge vents and intake vent. Find out what Flagship recommendations are.

 

[Capecodder]

My recent install of new westbo AC is SW Florida was if ran the fan in Automatic it froze up every night, if the fan is set to medium or high very infrequent freeze ups.

Not as quiet but AC is needed... River water is In the 80°s already

 

[caltexflanc]

Scanning through this, I haven't noticed the Occam's Razor question: what does your return air filter look like?

 

[Olebird]

Looks like it took a pretty rough truck ride! Bet it's leaking.



As for air flow issues, replacing 8K btu with 18K is a huge increase! I would stop guessing, measure air & water flows and temps - as well as voltage and current at the input terminals and share that with the designers who know the margins of their designs.


HVAC is not a black art or witch craft, it's a science and despite some popular beliefs .... if you do the math it can be made to work!


Might make a good meat locker!!

Well, it may have sustained damage. I did forget to mention that this is what it looked like when it came off the truck. I did let Flagship know immediately but the unit didn't look like it sustained damage.

 

[Larry M]

... this thermostat is about 4 to 5 degrees off. I guess because of the way it’s mounted if we set it to 72 it runs until our salon shows 68 on my weather center screen. If we set it at 75 the salon reads 72.

I wouldn’t worry about the thermostat being 4-5 degrees off. It’s a relative indicator in most cases. Sort of like you’re refrigerator/freezer where you have numbers for temperature control and 2 doesn’t freeze the lettuce but 4 does. Comfort temperatures on your thermostat for AC will different than for heating.

 

[BrisHamish]

To the OP,

I agree it sounds like an airflow problem.

One possible suggestion for you. When I installed my new Dometic AHU in the forward cabin it too froze over. We cured it in two ways - more airflow, and secondly (and this is the part that may interest you) the Dometic unit can be programmed by a tech to go into ‘defrost’ mode automatically every now and then such that it does not freeze any more.

Don’t know if your brand can be programmed with an ‘auto defrost’ - might be worth asking the manufacturer.

Hamish.

 

[FF]

"I am not aware of any way overcharge of refrigerant can cause frosting. under charge yes."


Should the freon be in such quantity that it can not all evaporate , and remains a liquid, even if just droplets , the suction return will continue the change from liquid to gas and frost on the beginning of the suction line is the result.

 

[ftmorgan]

A/C Problem

Typically frost on the evaporator coil and /or return (suction lime) indicates a low charge on refrigerant. I know these come as a package but may have left factory like that.

 

[Reelhappy]

I did a very similar update and had the same issue. My unit would randomly freeze based on temp and humidity. I added a single 3" duct into the head and problem was solved after a year of struggle.

 

[Peter Pan]

About your AC system freezing. Let me explain without going on details. The system freezes because of two main reasons. One, lack of enough AIR FLOW though the evaporator coil (the cold coil that handles air inside the air conditioned space). Could be a bad blower motor, a clogged filter or clogged coil, etc. Check and fix motor or clean air filter and/of coil.
The second option could be not enough refrigerant in the system. This lack of refrigerant charge causes a low pressure which lowers the evaporating temperature of the refrigerant and begins to freeze. Check the correct pressure for the specific refrigerant being used.
Hope it helps.

 

[FoxtrotCharlie]

About your AC system freezing. Let me explain without going on details. The system freezes because of two main reasons. One, lack of enough AIR FLOW though the evaporator coil (the cold coil that handles air inside the air conditioned space). Could be a bad blower motor, a clogged filter or clogged coil, etc. Check and fix motor or clean air filter and/of coil.
The second option could be not enough refrigerant in the system. This lack of refrigerant charge causes a low pressure which lowers the evaporating temperature of the refrigerant and begins to freeze. Check the correct pressure for the specific refrigerant being used.
Hope it helps.

What he said! As a landlord 90% of the time it's low refrigerant.

 

[TBW]

I have a 36,000 btu flagship marine ac.
It is well made; solid product.
When I first got it i had to add a dedicated cooling water pump and lots of air flow. it runs well and really cools.
However-
There was extensive discussion before I ordered it about where it was going to be installed and how it was going to be used. Jump to the end --- it has a one speed fan! it is very loud. And most importantly, my wife is very unhappy. it will be a few months before it rises to number one again but it will go over the side next time i am in 2000 ft of water and be replaced with something quiet.
Flagship's interest in one speed fans (never mentioned) and loud noise is zero.
You might need more air or more cooling water or both for yours.
TW

 

[Duvie]

Toocoys, your problem is as many have posted. It sounds like you went from 8k btus to18k btus without making any modifications to ductwork or wiring. Lack of airflow is most likely the source of your freezing up. Probably more to do with the supply ducts as you already have forced more air at the suction side of the system (that evaporator is tight to the bulkhead though.

Keep in mind as ambient temp goes up and your cooling water temperature goes up you are going to see a significant increase in amp draw from the unit. Make sure your wiring can support the FLA on the compressor data plate.

 

[bykpjfk]

I have the same boat as yours in 40'. I originally replaced the Dominic 12k btu unit in the forepeak with a 12k Webasto FCF series. Way too much cooling, too little compressor time. So I swapped out the 16k btu Dominic in the salon with the 12k Webasto unit, and the 12 k outperformed the old unit. I then placed a 6k btu FCF series in the forepeak, and everything is perfect.

I'm in Florida, spend summers in the Bahamas (well, not this year) and Keys (still hoping for that) and we like it cool.
My suggestion would be to move that 18k to your salon, and put a 6k something under your berth. I think the improvements made in a/c units will more than make up for the smaller size.
I helped a friend replace his a/c with your brand, and was impressed with the build quality. I don't think you have a faulty unit, just way too much a/c for the area.
Dan

 

[TWedd]

"I am not aware of any way overcharge of refrigerant can cause frosting. under charge yes."


Should the freon be in such quantity that it can not all evaporate , and remains a liquid, even if just droplets , the suction return will continue the change from liquid to gas and frost on the beginning of the suction line is the result.

Frost can be caused by inadequate air flow or low air temp. an overcharged system will keep the pressures high enough to prevent freezing. until the liquid returning to the compressor takes out the compressor!
A properly charged system will freeze if it has low air flow or temp, or a restriction in the metering device.
An over charged system will run high pressure and temps, be inefficient with poor cooling. will eventually kill the compressor due to high temp, high compression ratio or liquid refrigerant flood back diluting the oil or breaking valves. no frosting.
Not trying to be argumentative, just happens to be something I know a little about.

 

[skipperguy]

What I haven’t seen mentioned in reading through the first few responses is the relative humidity of the Return air. In doing my DIY central air installation a few years ago (which was very successful) I learned that sufficient airflow across the coil will prevent frosting and freezing. In so far as my reading went relative humidity of that air was not mentioned but could be important.

 

[Duetto]

we swapped out a 12k cruisair with a 16k dometic on our mainship pilot. had the exact same problems. based on dometic you need about 90 sq in supply ducting and about 200 sq ins return. we took the unit out and installed it in our other boat which had an older 16k unit. it worked perfectly.

i'd be figuring out how you are going to add duct capacity.

 

[toocoys]

So I tore everything apart today, cut a hole in the wall and turned the unit 90 degrees. This put the fins facing directly outward to the ambient air in the room. There is a significant change in the amount of air coming from the ducts. It’s ran for two hours and this is the result. About the only other thing that I can do is set it in the middle of an open room.

This photos is looking into the return hole.

 

[toocoys]

Ok. Here are some better photos.

The return hole (grill is off) is 13”x11”. My last hope is to open this up and allow more air in.

I have a 6” duct coming off that feeds two 5”x10” vents, and a single 4” duct supplying a 4” round vent in the head.

 

[Duetto]

the last pic had you returning supply directly into return. i think that's a no-no, duct has to exit way away from return,

 

[toocoys]

the last pic had you returning supply directly into return. i think that's a no-no, duct has to exit way away from return,

The duct exits above the bed, on the other side of the room. One vent goes into the salon, and the other vent goes into the aft bedroom. There is at least 6 feet between the vent in the room and the return, and there is a at least 12 feet, and a doorway between the salon vent and the return.

 

[toocoys]

Vents and return.