1969 Chris Craft Roamer 46 Refit: DIY Marine AC Raw Water Pump Controller

I’ve got three Flagship Marine air conditioners on the boat–16k in the salon, 12k in the aft stateroom, and 9k in the V-berth–and one March mag-drive pump (model BC-4C-MD) that needs to push raw water to all of them should any one of them call for it. Marine AC pump control boxes start at $300, but I thought I might be able to DIY something as good or better for far less.

My Flagship AC units have 24VAC terminals that call for the raw water pump to turn on. So I just needed three 24v relays that can handle the load from the March pump.

I bought three Omron G7L-2A-TUB-J-CB-AC24 general purpose relays for $20 each on ebay

The relays take that 24v signal and will pass 120v to the pump. They’re rated for 25 amps, so they’re overkill for this application. That’s not a bad thing.

I’ll mount the relays in a generic water-resistant electronic project box ($12 on ebay)

A little tight, but this will work fine

I used a Sharpie to mark where the holes for mounting screws need to be

Back at the garage, I drilled the screw holes and holes for the cables to pass through

Stainless screws threaded into the holes from behind

Stainless nuts and washers attach the components to the project box

Next, I installed the cable connectors in the holes I drilled in the project box

I installed the pump control box up and out of the way near the pump

Line voltage for the pump courtesy of the big salon AC unit

Neutral and ground pass through the terminal strip to the pump. 120v line voltage is routed to the “IN” side of each of the relays.

“OUT” side of each relay is daisy-chained to the LINE terminal for the pump

If any relay energizes (or all of them) the pump will see the same 120v and start pumping.

Aft stateroom 24vac pump call line

Ditto for the salon…

…and the V-berth

Done

And that’s a wrap for the pump controller. Total cost was around $100, and there are no proprietary boards or components.

Next up in our 1969 Chris Craft Roamer 46 Refit: Major System Test — Air Conditioners