Marine A/C - please educate me

[sdowney717]

You can swap propane for r22, it is an almost perfectly matched refrigerant, and typically uses 40% less propane than r22 to charge. Propane is fully compatible with mineral oils or most any refrigerant oils.
The only suitable propane to use which is clean and dry that you can just buy yourself is the kind used for the small torch bottles.
Charge to low side 60psi, high side 210 psi at 85*F outside temp is about right.
Attitudes to hydrocarbon refrigerants have improved a lot recently.
But also mark what you charged the unit with because who knows what someone in the future will do.
EPA has ruled propane refrigerant does not have to be recovered, it can be vented as it has an extremely low GWP and is naturally occurring in the environment.

OF COURSE, unit must be evacuated, you cant leave air or water in the system.
One advantage, propane runs at lower pressures than r22, so less amps is used and compressors and parts last longer since propane is naturally lubricating being a complex hydrocarbon, it is also a bigger molecule and does not leak as easily.

"Even though, R290 is exempt from the EPA’s Section 608 refrigerant
recovery regulation, it is recommended that R290 be recovered.
A recovery system is available (CCP# 145455)."
https://www.google.com/search?ei=JH...hUKEwjhmca7yr7jAhVmh-AKHY9cD70Q4dUDCAo&uact=5

 

[dhays]

Somehow I’m not entirely comfortable with charging an AC system which has lost its refrigerant with propane. I have a propane stove and oven. I’m pretty careful about any potential propane leaks. When not actively using the the stove, I close the propane tank which is located in an outside closed compartment which drain overboard away from any doors, vents, or windows.

Using propane in a system located in an engine or bilge space gives me pause.

 

[wkearney99]

Using propane in a system located in an engine or bilge space gives me pause.

Likewise, boats have plenty of other reasons they can explode/burn, I'm not sure I'd willingly introduce another one.

This seems like an area where ponying up the money for a proper repair seems a lot more sensible.

 

[sdowney717]

Somehow I’m not entirely comfortable with charging an AC system which has lost its refrigerant with propane. I have a propane stove and oven. I’m pretty careful about any potential propane leaks. When not actively using the the stove, I close the propane tank which is located in an outside closed compartment which drain overboard away from any doors, vents, or windows.

Using propane in a system located in an engine or bilge space gives me pause.

Lots of new freezers and fridges are being charged with propane, more so outside of the USA. But it is coming on the transition.

Actually low side is a little higher than 60 psi, you want it to evaporate properly into the evaporator and here he is using 68 psi for the low.

 

[OldDan1943]

Likewise, boats have plenty of other reasons they can explode/burn, I'm not sure I'd willingly introduce another one.

This seems like an area where ponying up the money for a proper repair seems a lot more sensible.

 

[Boat]

Somehow I’m not entirely comfortable with charging an AC system which has lost its refrigerant with propane.

Same with refrigerants that are mixtures. A leak changes the mixture and changes the properties of the refrigerant. The small, light molecules escape first. That's the short, oversimplified version, leaving out the exceptions and conditionals.

 

[ProMaritime]

Not much except one is water cooled and the other is air cooled.

 

[sdowney717]

The BIG problem in the eyes of the regulators about refrigerants is the global warming potential. All the unnatural fluorinated based ones are in the multi thousand figure, while propane's number is just 3.
And fluorine is expensive, its main source is from China mining.
They caused a worldwide shortage a few years ago driving up the prices a lot.
R134a also has a super high GWP number.


https://www.hvacrschool.com/changing-refrigerants-matters/

Its honestly coming our way, using propane as a refrigerant. Regulators are allowing increased charge amounts, now at 150 and soon to be 500 grams.

R1234YF, uses fluorine, a limited natural resource sourced of course from China, is very very expensive, and if it burns (as it is flammable also), the gas will turn into hydrofluoric acid which is extremely deadly and dangerously corrosive. Yet they are putting this gas into hundreds of millions of cars.

When using propane charge to low side super heat number of 10 to 16*F or so.
If you study that you will find out how, and its easy with a temperature probe. Too much superheat, its undercharged, too little superheat its overcharged. By charging by superheat, your determining the correct amount of refrigerant in the evaporator.

the superheat and the subcooling numbers are useful in diagnosing if an AC is working ok or not.

I am posting on this for general info about how these things work for interested people to learn, and so I can find the links easier myself.
https://www.contractingbusiness.com/service/subcooling-and-superheat-superheroes-system-charging
http://www.refrigerants.com/pdf/NRI-R290-SS.pdf

And at least on my cruisair unit, I have liquid receivers on the lines near the ports, (as designed by OEM) so my system can tolerate a lower superheat, less danger of slugging the compressor with liquid refrigerant. Compressors pump gas not liquid.
The old ones dont typically have the TXV valve feeding the evaporator.

 

[hmason]

I have not read this entire thread but I would like to pass on a tip that has worked for me numerous times including today! If the water output from your ac pump declines suddenly you might have something blocking your though hull pickup such as a plastic bag or other debris. My simple solution is to shut down the ac. Then start your engine(s), make sure you are firmly tied to the dock or anchored securely and then put the gear(s) in reverse. The prop wash under the boat will clear the blocked pick up.

 

[sdowney717]

Good idea about reversing. On the hull I have a large bronze screen with drilled holes.
its been ok, but I have wondered if it would be better to strain the water in the bilge.
I can unscrew the valve, and poke something through to the outside, but with that dish plate like strainer, I cant do it. But so far nothing has blocked it.
Then gen though did get blocked twice, once with grass, once with a jelly fish sucked in. The internal strainer was also not much use as the blockage stayed mostly in the thruhull. When I unscrewed the valve to see whats up with it, I saw this gelatinous mass and I could not poke it free. I took the dock hose and tried flushing it and took a while to get rid of it even with 60psi hose on there. i have sometimes seen real big jellies like a foot across in the marinas.

If the cooling water flow stops, the AC has a high pressure cut off. PSI on the high side will rapidly climb to 400 psi and then it will turn off the compressor only.

I am designing a way to turn off the compressor if the water flow stops. I am using a SUPCO Pressure Sensing Switch,1-1/2" D, NS2000031, it can adjust from 0.1 to 1" WC about 1 psi. That can turn off a relay in series with the high pressure cut off switch.
That will shut off the compressor before it has a chance to overload the high side with 400 psi.

My plan is connect the 1/4 inch tubing to the pump output at the pump outlet. So when pump is actually pumping water, the switch will click on, and turn on the relay allowing the compressor to run. When water flow stops, supco switch turns off, turns off relay, which turns off power to the compressor.

I have the older style auto resetting high pressure cut off switch, so if I leave the boat with AC running and water flow stops, it will endlessly cycle the compressor to high pressure over and over and over...which I think is too much continual stress on it.

If the water flow magically restarts, the AC will also restart automatically.

Newer marine AC if they trip off on high pressure, do not come back on. You have to manually reset the switch. If you setup a circuit to test for water flow, then the AC wont trip its high pressure cutoff and could restart automatically if the water flow comes back.

 

[sunchaser]

A 20 degree differential can be rather dramatic. Today I was working outside. I dont know the outside temp but when I came inside the temp inside was chilling. LOL

No problem for AC to cool a house or office to more than a 45F differential. Ditto your car too. Gas expansion and contraction is the key. Replace air with water and same principles at work. I seem to recall PV=nRT covers the science.

This past week gas expansion and contraction has been required in AK. Hot days and cool nights, not beans, were the culprits.

 

[OldDan1943]

Good idea about reversing. On the hull I have a large bronze screen with drilled holes.
its been ok, but I have wondered if it would be better to strain the water in the bilge.

If the cooling water flow stops, the AC has a high pressure cut off. PSI on the high side will rapidly climb to 400 psi and then it will turn off the compressor only.

Newer marine AC if they trip off on high pressure, do not come back on. You have to manually reset the switch. If you setup a circuit to test for water flow, then the AC wont trip its high pressure cutoff and could restart automatically if the water flow comes back.

I have created a gadget that allows for back flushing of my sea strainers. You can see the pic if you look at my bio. There are also plastic cap that screw on the strainer cap. This can be useful for back flushing the strainer. Of course if the installed hull strainer is plugged up, back flushing may not be the answer. A plastic bag can smoother the A/C or ME or generator inlet. Time to dive the boat. It should take less than a minute to remove the grass or plastic bag.

 

[Mark P]

So let's keep educating - at least me - why don't I see more Trawlers with all-in-one roof top a/c units that use freon? Is it power requirements? My window a/c unit in my garage in Atlanta works quite well and it was near 95 yesterday and my area it cools is about the width and length of a good-sized Trawler.

 

[sdowney717]

So let's keep educating - at least me - why don't I see more Trawlers with all-in-one roof top a/c units that use freon? Is it power requirements? My window a/c unit in my garage in Atlanta works quite well and it was near 95 yesterday and my area it cools is about the width and length of a good-sized Trawler.

Sure works fine for RV's also. And can be a lot cheaper and as it is self contained, you dont need to pay an expensive HVAC tech to install it or fix it.

It just is not aesthetically nice to have a window unit. And they probably corrode easier. I have thought one of the floor room AC's might be ok, needs a hole in the side to vent the hot air. I like having my hatch unencumbered. I might consider cutting a new hole in the roof for an AC, if I did not have a marine AC.

 

[OldDan1943]

Sure works fine for RV's also. And can be a lot cheaper and as it is self contained, you dont need to pay an expensive HVAC tech to install it or fix it.

but the required hole is rather large

 

[wkearney99]

So let's keep educating - at least me - why don't I see more Trawlers with all-in-one roof top a/c units that use freon? Is it power requirements? My window a/c unit in my garage in Atlanta works quite well and it was near 95 yesterday and my area it cools is about the width and length of a good-sized Trawler.

Noise, space, aesthetics? Loud, bulky, ugly? But probably most importantly, there's a much more efficient heat transfer medium available... the seawater.

 

[wkearney99]

I have created a gadget that allows for back flushing of my sea strainers.

Did that with the strainers on my previous boat to ease winterizing. I put a hose fitting into a strainer cap and let the system pull antifreeze in from a 5 gallon jug. Worked great for the AC & genset. No reason why it wouldn't work likewise to push water back out, but you'd want to be careful about pressure and the glass liner in most strainers. No point in blowing out the cylinder or any connected hoses accidentally, as water pressure from a shore connection could be a problem.

 

[OldDan1943]

Not much except one is water cooled and the other is air cooled.

Finally, someone agrees with me.
I guess that means, we are both wrong. SHRUG

 

[OldDan1943]

No reason why it wouldn't work likewise to push water back out, but you'd want to be careful about pressure and the glass liner in most strainers. No point in blowing out the cylinder or any connected hoses accidentally, as water pressure from a shore connection could be a problem.

I use the pressure created by the boat's water pump.

 

[Les_Garten]

Got it, guys. So, here in the southeast US, where the water temps are often 80+F this time of the year, a marine A/C would be practically useless, huh?

South Florida-- Air temp 92 degrees, humidity sky high, yet my car's AC works great.

 

[OldDan1943]

South Florida-- Air temp 92 degrees, humidity sky high, yet my car's AC works great.

My boat gets cold too.
I turn it on when the boat's humidity gets high again.

 

[FF]

Most folks are limited by the power available at home or visited power poles.

Your car air cond compressor can take 10HP from the engine to cool the tiny cat interior.

10HP from 120v requires a lot of power hoses!

 

[Boat]

When using propane charge to low side super heat number of 10 to 16*F or so.
If you study that you will find out how, and its easy with a temperature probe. Too much superheat, its undercharged, too little superheat its overcharged. By charging by superheat, your determining the correct amount of refrigerant in the evaporator.

the superheat and the subcooling numbers are useful in diagnosing if an AC is working ok or not.

And at least on my cruisair unit, I have liquid receivers on the lines near the ports, (as designed by OEM) so my system can tolerate a lower superheat, less danger of slugging the compressor with liquid refrigerant. Compressors pump gas not liquid.
The old ones dont typically have the TXV valve feeding the evaporator.

The total superheat method is the most accurate method of charging fixed orifice or capillary tube systems

Subcooling on systems that use a thermostatic expansion valve (TXV)

They said an expansion valve regulates superheat so charge by subcool in that case. Just wanted to draw this distinction between the two types of systems.

I'm impressed that you brought this up. Most people never dig this deep. I'm not a AC tech or engineer, just self taught.

 

[sdowney717]

They said an expansion valve regulates superheat so charge by subcool in that case. Just wanted to draw this distinction between the two types of systems.

I'm impressed that you brought this up. Most people never dig this deep. I'm not a AC tech or engineer, just self taught.

I enjoy learning and doing too. I have always wanted to know how things work or can be made to work. I also like doing projects and making modifications to make things work better. The side effect is I save money, but I also end up fixing almost everything far past where most people would go.

Like how many would make their own exhaust adapter for an old engine where it can no longer be purchased?
https://goo.gl/photos/9enZHLqh9tCwRjDe7

 

[Wayne]

Hi, On the Celestial, there were two ACs. It had the raw water set up so that the pump served both units. In experimenting, I found that rate of water flow through condensers made a large difference when the seawater temps got above 80*F. When the flow to the forward (cabin) AC unit was shut off, the entire flow went through the aft cabin AC, resulting in better cooling on hot, humid Florida nights. A larger/higher capacity pump would have made better flow through both, but we seldom used the boat when it was too hot, as we had to hibernate inside to keep from cooking - I had near-heatstroke - and high temps really affect me.


The other point I wanted to make was that on most, if not all, boats I have been associated with, the AC unit could only cool the air by about 15*F in a single pass. A small cabin area will result in more multiple passes in a given time. This, of course, results in lowering the area temp by a much larger amount over time. How well insulated the boat is make a huge difference in rate of cooling. The Celestial's aft cabin/sleeping area's 12000 BTU (IIRC) AC unit could cool the area to 72-73*F after running all day in 85-95*F air temps and then coping with the heat radiated from the twin Cummins 6BT5.9M engines, transmissions and 500 gal (total) fuel tanks, plus the (often) 80+*F seawater. I usually started the genny shortly after anchoring as my wife preferred to cook on a small electric frying pan and electric pot and we ran both AC's until we retired, then shut the 16000 BTU (IIRC) cabin AC off.

 

[Grandbanksgreg64]

Can someone explain to me how a "marine" air conditioner works as compared to a typical RV rooftop type or window unit A/C, please?

Came across this description of each A/C type... helpful:

WHAT IS A SELF-CONTAINED MARINE AIR CONDITIONER?

Self-contained marine air conditioners will typically be mounted in a locker or under a bunk, operating by drawing in water from a thru-hull connection and combining it with eco-friendly refrigerants that create cool air. This air is then blown throughout the space by a blower motor and fan.

WHAT IS A SPLIT SYSTEM MARINE AIR CONDITIONER?

A split system has the a/c components split between two separate units (condensing unit and evaporating unit) installed in different locations and connected by insulated copper tubing through which the refrigerant travels.

WHAT IS A MARINE CHILLER / CHILLED WATER A/C SYSTEM?

Chilled water marine air conditioners consist of a chiller, located in the engine room, that cools (or heats) fresh water, then pumps it through an insulated piping loop to air handlers located in the living spaces, where the air is cooled (or heated).

Source: https://citimarinestore.com/en/184-marine-air-conditioning-boat-ac

 

[Rcsands1257]

Do HVAC units use a lot of electricity like a normal home ac unit. Do they work off your batterys or do I need to turn my genset on. Just bought the boat and have never had a hvac unit before.

 

[Bmarler]

Do HVAC units use a lot of electricity like a normal home ac unit. Do they work off your batterys or do I need to turn my genset on. Just bought the boat and have never had a hvac unit before.

It pretty much depends on the size and style of the system. Most ac units are ac, so genset or shore power required. I’d try to get familiar with what you have so you fully understand the function. There will likely be a raw water pump involved too, so there will be a through hull fitting for that pump which needs to be open for it to work.
I’d count on it drawing 12-15 amps or so.

 

[Shrew]

Do HVAC units use a lot of electricity like a normal home ac unit. Do they work off your batterys or do I need to turn my genset on. Just bought the boat and have never had a hvac unit before.

You would have limited time running an AC on a house battery. It would require an inverter, since the raw water pump and the A/C unit is running on 120VAC.

You would need a generator or shorepower. I have been able to run my 5K BTU unit on a Honda 2K portable generator. A larger A/C would need an EasyStart (Soft Start) to reduce the initial spike during start-up if you're using a small generator.

 

[mvweebles]

Do HVAC units use a lot of electricity like a normal home ac unit. Do they work off your batterys or do I need to turn my genset on. Just bought the boat and have never had a hvac unit before.

By far, the most common marine AC units on boats in the 30-50 foot range are self-contained units that use seawater for cooling. They are 120VAC (US) and are comprised of two main components: a seawater pump (120VAC and must be installed below waterline as they are non-priming); and the all-in-one A/C unit itself that has a blower, condensor, and evaporator in a single chassis. After initial install, they are pretty easy to replace. They often last over 10-years of constant use. Many have both heat and cool functions.

Power draw for my 12k Btu unit is around 1A (120VAC) for the pump, and 8-10A for the A/C. My 6K Btu unit for my stateroom is 1A for the pump, and around 4-5A for the A/C, which is possible to run off the inverter with a large battery bank and hi-output alternator.

One note - the start-up amperage of the compressor can be quite large - 30A-50A for an instant is not uncommon and can overwhelm power. A Soft Start capacitor buffers this load - some units have this included in their system architecture, or you can add it during installation.

Common manufacturers of Marine A/C units are Webasto, Dometic, and MarinAire, though there are others I'm sure.

There are also 12VDC versions of the above that claim improved efficiency, but they are quite a bit more expensive and from much smaller manufacturers, so a bit more eploratory in my opinion.

Good luck -

Peter