Modify Car A/C for Use on Sailboat - Thoughts?

[Steve W]

The average automtive a/c for a large sedan is 3.3 tons? Wow! My Grand Marquis' A/C system could not come close to cooling our home here in sunny Florida. No time to research now, but it seems I remember that most automotive compressors are 1/2 -3/4 ton capacity, but it sounds like you have already researched that. I just don't see how you can move enough air thru a large enough air-cooled condensor and safely exhaust it in a safe & reliable manner to effectively cool the inside of a boat without heating up the engine room. A car A/C condensor fan really moves a lot of cfm. I hope you can make it work and please let us know how it turns out.

[Fishman_Tx]

That's what it said, but I think they may be relating equivilancies. I've seen stand alone units for RV or school buses that use slightly larger engine-mounted compressors rated 66,000 btus, though.
Re: moving air - oh I can move enough air. have you ever seen what an automotive squirrel cage fan (NOT in the auto) can do? Oh I can move the air. The problem was getting the heat out of the compartment and besides I didn't want to have to use such a power hog fan on the condensor when I already have to use one on the evaporator to cool the cabins. So, here we are again. But a couple of ideas have come out of all this.......

Then again with all this airflow, maybe I'll just point the dorades forward and hank on some sail. We don't need no stinkin' wind!

[READY2GO]

I have wondered about making an a/c system to mount on a hatch using a coil, fan and a bilge pump. I don't know if it will work, but my thought was to make a housing with the coil and 12 volt fan in it to sit on the hatch opening (with a condesate drain) and drop a 10 -12 feet long hose over the side with the bilge pump attached.
If the water is 65 or 70 and the air is 85 or 90, I think it would get rid of some humidity and cool a little (not sure if enough) and everthing is 12 volt and low amps. The air would be recirculated, no outside air.

Any thoughts?

[Fishman_Tx]

Don't see why not. Just making your own semi-version of a swamp cooler. Or maybe closer to a chill-water system but here the water is already chilled. But I think that would only work in the northern latitudes.

[Event_Horizon]

Hi, friendly neighborhood engineer checking in.

First off, I'd make sure the A/C unit was using freon. Car A/C units have been using R-134a refrigerent gas for awhile now and mixing the two is a terrible idea.

Not making use of the ocean to cool the condenser is a bit on the silly side. I don't understand why you couldn't increase the capacity of the engine water cooling system and use that to cool your condenser. It seems more costly to impliment a shabbily built air cooling system that will almost certainly eat tons of power and still not achieve the minimum volumetric flow rate required.

Also, opening up your engine compartment to the environment via. inlet-outlet ducts is probably a terrible decision reguardless Seawater/Ocean air is HORRIBLE on EVERYTHING and will cost you dearly. The only way to avoid this is to build a seperate tunnel for the air to travel through and over the condenser...but if you do that you might as well water cool it.

Either way you need to properly coat the condenser with anti-corrosive heat exchanging compound if you want the thing to last more than a year at sea.

[READY2GO]

Yes, it would be like a water chilled system, but using already chilled water from 10 to 12 feet below the surface. We sail on Kentucky Lake. This far north in a lake, the water is pretty cool that deep (its very green so the sun does't get down that far). Can't wait to get to the islands and clear water. You wouldn't want to snorkel around here. But the landscape is good, and the wind fair.

[LtBrett]

Most automotive a/c components are aluminum. Not much concern for rust.

As for sizing your fans, remember an a/c is a heat pump. What you pump out from you cabin must be pumped out from your engine room. This suggests your condenser fan must be at least as large as your evaporator fan.

And the a/c compressor is rated at a certain rpm. An s-10 redlines at what, 5500 rpm or so? Cruises at 2500? Your current pulley will get you close enough, but you do have some headroom if you want to undersize your pulley.

I can't wait to hear how well this beast works!

Brett

[Event_Horizon]

Yes, chances are your condenser is entirely aluminum (depending on model it could also have some copper). Yes it doesn't rust...should you still treat it...OF COURSE! Aluminum doesn't rust but it is NOT corrosion proof. If you were sailing in a sea of distilled dysani water then sure, don't treat it. Unfortunatly the ocean doesn't have a neutral PH and that means that unless you have high chromium alloys (which you dont) or a chrome plated condenser, treat it against the harsh environment if you want to use it for awhile.

As for fan sizing (again please water cool the stupid thing, its easier and better)LtBrett says, "an a/c is a heat pump...This suggests your condenser fan must be at least as large as your evaporator fan", I'd say if you want it to actually work. Your condenser fan must be significantly larger than your evaporator fan. It turns out that thermodynamically this is going to make sense because you are attempting to reject heat into a hot environment. This means that there is less energy transfer so all you can do is increase the airflow (or water cool it for ease and performance).

[Dellin]

A pic of the condenser would be helpful, I keep coming back to water cooling it is so much more efficient.

Assuming the condenser is a pipe in an S shape patten with cooling fins attached. I am thinking if you carefully cut away a section of fins with an angle grinder so you can lay a water pipe of the same diameter along side pulling them together with cable ties using heat-sink compound between them. You may not even need to cut the fins if you can get a good enough thermal connection between the water pipe and the fins.
The only other method I can think of in converting your existing condenser is to submerge the condenser and water pipe in a mineral oil bath and using the oil as a transfer medium but that could get messy unless you have a container that is well suited.

YouTube - Oil Cooled Computer

[Fishman_Tx]

Come on guys...
You know, some of you still aren't reading what has been written in my posts or you wouldn't ask some of the questions you ask. I'll refer you back to post #1,6,7,15,21, and 27. Essentially all my posts on this thread and READ THEM. Pic? This an existing car ac system. All you gotta do is look under your hood and in front of your radiator to find the condensor(unless you live in big city and are public transportation user).

And NO I am not going thru the expense of pumps, lines, and fittings nor am I coring any new holes in my boat for thruhulls (or any other new "point of failure"). Get off the water cooling plz, it's NOT going to happen. Refer to post 21. Unless your discussing it for your own ac systems. If YOU want to make a water cooled system, OK fine!

Take copper line and fittings of the appropriate size for your system and, a piece of 4" PVC pipe with 4" end caps to match, and 2 water line fittings of choice WITH valves for each end. Coil the copper tubing to JUST FIT into the 4" pipes ID, insert tubing coil into pipe, drill end caps, attach all water fittings to end caps, attach end caps leaving 6"-12" of copper tubing out each end cap for trimming and attaching fittings, trim and attach fittings, caulk EVERYTHING with 3m 5200 and let set. REMEMBER: Silicone caulk WILL NOT HOLD UNDER HIGHER PRESSURES from the pump. If you use it, it will eventually (if not immediatly) blow out. Attach to water pump system. Attach ac freon lines. Prep and fill freon, etc etc ad nauseum.
There you go! Voila! A heat exchanger. How big you make it is up to you.

Now that we got the area of WATER COOLED systems covered and out of our hair......

An air-cooled system has no points of failure that are a danger to the vessel and is WAY less expensive to install AND maintain. Thruhulls require seacocks, and NONE of this is cheap. If a blower fails, just replace it with the $30 spare from your parts locker. If the clutch or the compressor fails, cut the belt. If a thruhull or seacock fails, YOUR SCREWED.

The KISS method works. Consider the potential ramifications of failure in all you do to your boat. Use common sense.

[GordMay]

Originally Posted by Fishman_Tx

”The Devil is in the Details”

Indeed.

Your original post asked for our thoughts on modifying a Car A/C for use on sailboat.
Although you admitted to the possibility of making a water jacket for it, you suggested you’d use 6" computer fans, then (wisely) moved on to Squirrel Cage fans.

The largest 250 CFM Jabsco Bilge Blower #35400 Series (250 CFM radial squirrel cage fan) cost about $200/each.
To actually achieve “almost” the 250 CFM rated airflow (NO S.P.), you’ll need two - 1 supply & 1 return/exhaust.
Thus, $400 worth of fans will ventilate nearly* ½ Ton of Air-Conditioning (6,000 BTU/H).
* Only nearly, because the 500 CFM/Ton rate assumes all ambient air, not mixed with elevated engine compartment air.

➥ Ventilation Blowers > Marine > Jabsco - ITT

I understand that you don’t want to hear about water cooling, and certainly not any negative thoughts, because “it’s going to happen”. Nonetheless, I reiterate my earlier opinion that, as you describe it, it’s not going to work very well, and certainly not almost “for free”.

Good luck, and I look forward to hearing in your September report, that I'm completely wrong.

[S/V Illusion]

I would agree with Gord. Sometimes hearing what you don't want to hear is difficult and understand that we are trying to be constructive

[s/v Jedi]

Fish,

You keep saying that you are not going to drill new holes, fit thru-hull fittings and seacocks and pumps for water cooling. This means you did not read some posts carefully enough!

So, I will try it more clearly: you are going to drive the compressor with the engine. This means that the engine is running when the A/C is on. It has been suggested by some posters, incl. me, that you can use the raw water flow of your engine. It's running, water is flowing, you can tap into it. There's even details about it in the thread, incl. options for converting the existing condenser for this.

I would guess that this will be more cost effective and more energy efficient.

Also, the evacuating and filling of the system can't be avoided anyway, I think.

cheers,
Nick.

[Intentional Drifter]

Well, maybe we'll all find that the laws of thermodynamics are really only "suggestions", after all.

ID

[David M]

You cant put something on the suction side of the raw water inlet and expect water to flow to the second device. It will need its own raw water pump. This is a bad idea anyways because you then increase the chance of introducing air into the engine cooling should something go wrong with the coolant condenser circuit. Give the condenser cooler its own raw water inlet. This of course means it will need its own seacock and strainer.

My gut feeling is it is best not to go the cheapest route from the beginning.