A comprehensive guide to choosing the right marine AC circulation pump. Covers Scot 67/68 series, Oberdorfer 107M replacements, magnetic drive options, sizing for BTU capacity, and installation tips from 25+ years of experience.
The seawater circulation pump is the heart of your marine air conditioning system. When it fails, your AC stops cooling — and in Southwest Florida's heat, that's an emergency. This guide covers the most common marine AC pumps, how to choose the right replacement, and what to expect during installation.
Marine air conditioning systems use raw seawater to cool the refrigerant condenser. The circulation pump draws seawater through a strainer, pushes it through the condenser coil, and discharges it overboard. Pump failure means no cooling.
Centrifugal pumps (Scot, Oberdorfer, Calpeda) use a spinning bronze impeller to move water. They handle high flow rates and are the standard for systems over 24,000 BTU. Magnetic drive pumps (March, Little Giant) use a magnetically coupled impeller with no mechanical seal — eliminating the most common failure point. Best for smaller systems under 48,000 BTU.
Scot pumps (now by WILO) are the original equipment on most Cruisair and Marine Air systems. The 67/68 series is the most widely installed marine AC pump in the industry.
Available in 1500 GPH and 2000 GPH configurations. Bronze construction with carbon/ceramic mechanical seal. Fits Marine Air P100, P120, P700, and Cruisair PS1500BX, PS1800BX, PS2200BX systems. Price range: $370-$860.
Higher volume for larger systems — 3240 GPH. Replaces Marine Air P7100, P7102, P7111, P7112. Price: approximately $1,175.
Oberdorfer's 107M series was specifically designed as a drop-in replacement for Scot 67 and 68 series pumps. The precision machined and balanced impeller provides extremely quiet operation — noticeably quieter than the Scot equivalent.
107MB-F25: Replaces P700, P700Z, PS2200BX. 2000 GPH at 15 feet of head. 3.44" impeller, 56C TEFC motor. ~$550.
107MA-F25: Replaces P120, PS1800BX. 1800 GPH at 15 feet of head. 3.0" impeller, 56C TEFC motor. ~$500.
Both models use 115/230V 50/60Hz motors and are true drop-in replacements — same bolt pattern, same port sizes, same electrical connections.
March MDX-3-5/8 is the standard replacement for King Air AC systems. Sealless magnetic drive means no mechanical seal to fail. 510 GPH, 115V. ~$280. The upgraded LC-3CP-MD adds a waterproof sealed motor for ~$350.
Little Giant 3-MD-SC handles systems up to 24,000 BTU (~$220). The 5-MD-SC handles up to 48,000 BTU (~$350). Both are sealless magnetic drive with open painted motors.
Calpeda CM series centrifugal pumps are common on European-built vessels and chilled water AC systems. The CM 22E-R (0.75HP, 220-240V) is IP54 rated and TROP certified for marine use. Made in Italy. ~$500.
Match the pump to your system's BTU capacity:
Under 24,000 BTU: March MDX-3-5/8 or Little Giant 3-MD-SC
24,000-48,000 BTU: Little Giant 5-MD-SC or Scot 67/68 1500GPH
48,000-128,000 BTU: Scot 67/68 2000GPH or Oberdorfer 107M
Over 128,000 BTU: Scot 78 series or KC2 high volume
1. Always replace the strainer basket and inspect the strainer body for corrosion. 2. Check all hose connections and replace any cracked or swollen hoses. 3. Use marine-grade hose clamps (316 stainless). 4. Prime the pump before first start — never run dry. 5. Check for proper water flow at the overboard discharge.
For most boats with Cruisair or Marine Air systems, the Oberdorfer 107M is our top recommendation — it's a true drop-in replacement for Scot 67/68, runs quieter, and costs less. For King Air systems, the March MDX-3-5/8 is the clear choice.
Call Accumar Marine Services at 239-323-9600 for same-day AC pump replacement in Fort Myers, Cape Coral, Naples & SWFL.
Beyond the obvious lack of cooling, you might notice unusual noises like grinding or humming, reduced water flow from the overboard discharge, or even a tripped breaker. Addressing these issues promptly can prevent further damage to your AC system, and Accumar Marine Services in Fort Myers, FL, can diagnose and repair these problems efficiently.
Absolutely. The Oberdorfer 107M series is specifically designed as a quieter, drop-in replacement for common Scot pumps, offering noticeably quieter operation. Accumar Marine Services can help you select and install the ideal quiet pump for your vessel, ensuring peaceful nights on the water in Cape Coral or anywhere in SWFL.
Regular maintenance includes cleaning the raw water strainer to prevent debris from entering the pump and checking for any leaks or corrosion around the pump housing and connections. For optimal performance in the demanding SWFL marine environment, it's also wise to have your system professionally inspected by experts like Accumar Marine Services in Fort Myers annually.
Yes, for King Air AC systems, the March MDX-3-5/8 is the standard replacement, known for its sealless magnetic drive which eliminates common failure points. For an upgraded option, the March LC-3CP-MD offers a waterproof sealed motor, providing enhanced durability in the marine environment. Accumar Marine Services can assist with selecting and installing the correct March pump for your King Air system in the Fort Myers area.
Matching the pump's GPH output to your AC unit's BTU capacity is crucial for efficient cooling and to prevent premature wear on the system. An undersized pump won't provide enough cooling, while an oversized one can lead to excessive power consumption and potential cavitation issues. Accumar Marine Services in Fort Myers, FL, specializes in proper sizing to ensure your marine AC operates perfectly.
