A/C intake manifold

I'm glad that our Mermaid A/C unit now resides in the dumpster at the marina. I've never had a unit that gave so much trouble. But I guess 1000gph is a lot of water. I didn't realize they made pumps with that capacity.

Bob

A March AC-5C-MD is a common pump to use in marine air conditioning systems.
It moves close to 1000 GPH and will handle close to 50,000 BTU.

The March LC-3CP-MD would be appropriate for a 16000 BTU system. It can handle up to about 25000 BTU systems. It moves close to 500 GPH.

On my little 5000 BTU unit I use a March LC-2CP-MD. It pumps less than 300 GPH.

Sceptic said:

“too much water results in turbulence and if there is any grit in the water it’s like a little sand blaster. It takes a while but you end up with little holes.”

Click to expand...

That's it. There doesn't have to be any grit, the high velocity will erode the tubing walls all by itself. If there is any contamination like a tiny barnacle sticking to the side of the tube it will create a cavitation bubble behind it that will fairly quickly bore a hole in the tubing wall and put seawater in the refrigerant that will instantly destroy the compressor.

That is the problem we are dealing with now, the builder installed a single pump large enough to supply 3 large chilled water units and the resulting high velocity eroded the tube sheets on all 3 condensers in just a few months and destroyed the compressor on one. We are going back with 3 properly sized pumps and a head pressure controlled VFD drive for each.

500 GPH is what all the documentation (pump and A/C Mfg'rs) recommend for a 15K-16K BTU reverse-cycle unit. I didn't notice the max flow rate, but it makes sense now. Anyway, I already bought the two pumps, one for each, not knowing where I'd end up putting everything.

For me it makes sense to have two separate systems. For now I have to feed them from the same through-hull. There is another unused through-hull in a convenient location for the forward unit, but it needs to be replaced. Next time the boat is out of the water, that will be one of my first jobs. Don't get me started about the idiot PO who used a ball valve from a home improvement store and an uncoated pine fairing block.

I have five A/Cs that run off a single pump. Works much better then those cheap plastic A/C pumps they try to sell you for big$.

NICE , centrifugal , no rubber vanes to wear out.

All the A/C pumps I've ever seen have been centrifugal pumps, that's why they require a flooded inlet.

Bob

Status update:

So far so good. The two pumps run fine together or separately. Initially at least, no air is back-flowing from the "off" loop through to the running loop. The A/C units work great in both heat and A/C mode. Next project, hook up the ducts and registers.