Upgraded thermostat options

[gotjeepzj]

My carver originally came with a 1986 16000 btu marine air. When I bought the boat I was told that it was just low on Freon...but the boat came with a 2006 18000 btu marine air, but no controls. I had my a/c guy wire my old controls to the new system. I’m wondering if I could upgrade to a thermostat that will turn the unit off and on like a house

[GordMay]

Greetings and welcome aboard the CF, gotjeepzj.

Yes.
Marine Air (now Dometic) Systems Air Conditioning Air Conditioning Controls
➥ Marine Air Systems Air Conditioning Controls | Tropical Marine AC
➥ https://citimarinestore.com/citiguid...ntrols-for-ac/

[GreenWave]

They make control pads (digital) where you can setup temp setpoints. Some models also allow automatic fan settings so it owuld then operate just like home.

[Coolerking]

That unit came with a Passport I/O control.

[a64pilot]

In order for you to upgrade one so that it will operate like a house I.E. fan only comes on with the compressor, you need a thermostat that senses the air temp at the thermostat, like a house does.
All Marine AC’s that I am familiar with sense the room air temp in the return air grill, so that it takes constant air flow to continuously know what the room air temp is.
That’s not an insolvable problem of course and I have seen some window units for houses solve that issue by running the fan for 5 min every 30 min or so.

[SVHarmonie]

Originally Posted by a64pilot

In order for you to upgrade one so that it will operate like a house I.E. fan only comes on with the compressor, you need a thermostat that senses the air temp at the thermostat, like a house does.
All Marine AC’s that I am familiar with sense the room air temp in the return air grill, so that it takes constant air flow to continuously know what the room air temp is.
That’s not an insolvable problem of course and I have seen some window units for houses solve that issue by running the fan for 5 min every 30 min or so.

It is most certainly not insoluable, at least two builders of small yacht AC units have solved it.

MarineAire AC units have both options. A remote themostat, or a fan that runs 30 sec every 10 minutes to sense air temperature at the return grill.

Mermaid AC units dispense with the whole problem by using a standard 4-wire household thermostat, which of course includes the temperature sensor. A much better solution, IMO, since controller issues are frequent sources of trouble, and you can swap out one of their thermostats at any hardware store with what ever controller options you might want to spend money for.

For sophisticated air conditioners, I have never understood the rational for the return air grill sensor--other than it is cheaper and ties the customer to your spare parts forever.

[Coolerking]

Are you cooling part of the room where the sensor/display is at?
Or are you cycling the air through coils and reading the effect over time?
The AC only knows what you are telling it, that means you pretty much need to measure the air temp at the return air path, and the fan needs to run to do this.
This becomes very apparent when you are trying to cool a pilot house with lots of glass on a sunny day.

Many of the marine hvac systems we install will default to the display to read the air temps if possible when the alt-air tsep is removed from the board.
These can be influenced by it's position in the boat, ie..in the sun.
Keep in mind that there are many many different ways to do marine hvac, in the end, its all about removing heat.

[gotjeepzj]

Thanks all. First let me clarify my original post. The boat had the optional 16000 btu unit installed when I bought it. It didn’t work. I was told it uses a can of Freon every 2 years and it was time to refill. Bad news. That was not the case. As soon As I put Freon in it, and turned to start, it would trip the breaker. Locked compressor. Good news...when I bought it he had given me a 2006 18000 btu unit. He was told it was good, but had never hooked it up, and it didn’t have any controls. I had our marina a/c expert check it out and he said the compressor was free and it had Freon. We hooked it up and he used my old controls on the newer a/c. I haven’t had problems in the year it’s been done.


Current situation is I run a 6000 btu window unit all day in the summer. Set on max cold and high fan it struggles to keep the boat about 84 degrees. I get home I turn on the main unit and the boat will cool off in about 10 mins. I don’t like having to leave the window unit on all day. And I don’t like the idea of leaving the blower and a/c water pump running on the main unit all day either. I was hoping I could use a thermostat of some sort that would kick on everything but then turns everything back off...cycling.

Currently the unit, return air, and biggest vent are located center of boat. I only have 2 vents and you wouldn’t believe how they ran the air to the bedroom.

I found the 3 knob conversions for $700+ but if I have to pay that much, I might as well pay $1700 and get a brand new one that comes with the modern digital thermostat. So I thought may I have other options and/or maybe I’m missing something.

[Pete17C]

A regular home t-stat and a couple of relays ought to do the trick.

[Coolerking]

On a factory original system,the water pump should only run when the compressor is running, i.e. the unit is cooling.
The fan will run all the time, as its designed to do, in auto modes, its speed will vary depending on the ambient/setpoint differential.

[Sailmonkey]

Originally Posted by Coolerking

On a factory original system,the water pump should only run when the compressor is running, i.e. the unit is cooling.
The fan will run all the time, as its designed to do, in auto modes, its speed will vary depending on the ambient/setpoint differential.

I seem to remember the old three knob units running the water pump continuously.

[gotjeepzj]

Originally Posted by Sailmonkey

I seem to remember the old three knob units running the water pump continuously.

That is correct sir. Continuous.

[Coolerking]

Originally Posted by gotjeepzj

That is correct sir. Continuous.

Only when asking for cooling, ever.
It's triac is wired into the same circuit that is the compressor L-1.
Keep in mind that the older 3 knob control needed you to switch from "on" to "run".
If it runs all the time then the triac is shorted closed.
The same applies for the compressor and the fan...in the older units, if the triac shorted closed, then it would cause the corresponding device to run on power up/breaker on.
And if the triac has burnt through.. shorted open, then they would not run at all...

[gotjeepzj]

Originally Posted by Coolerking

Only when asking for cooling, ever.
It's triac is wired into the same circuit that is the compressor L-1.
Keep in mind that the older 3 knob control needed you to switch from "on" to "run".
If it runs all the time then the triac is shorted closed.
The same applies for the compressor and the fan...in the older units, if the triac shorted closed, then it would cause the corresponding device to run on power up/breaker on.
And if the triac has burnt through.. shorted open, then they would not run at all...

That makes sense actually. One of my biggest issues is when the thermostat works and the compressor cycles off, it’s still pumping 90* lake water through it turning the ac into a heated...same thing in the winter.

Where is the triac located and can it be replaced?

[Coolerking]

It's in the control box for the unit itself, usually mounted to the inside surface of the box itself, or, if you have multiple units running on one pump, it would be in the pump relay box.