C&C 35-1 Refrigeration Install
After years of digging through ice to find a beverage, I decided to install refrigeration on
'Touche', a C&C 35 Mk1. The selected system was an Isotherm 3701 ASU, an air cooled
unit with a cold plate for a box of up to 7 cubic feet. The existing box was calculated to be
about 6-6.5 cubic feet.
In order to get an idea of the existing ice box insulation, an access was cut into the bulkhead
on the inboard side of the box. This required removal of the sink. About 1 1/8 inch of sheet
foam insulation was discovered.
An attempt to add additional insulation was marginally successful due to the restricted opening
between the insulation. Pour foam insulation had been added to the outboard side previously.
The cold plate was installed on the aft side of the box. After careful measurement, a ¼ inch pilot
hole was drilled through the ice box skin and bulkhead behind. Then a hole was drilled from each
side with a 1 3/8 hole saw using the pilot hole for alignment. Decent insulation can be seen in the interior
picture below.It is assumed this is some of the pour foam insulation that was added on the outboard
side and not insulation from the original build.
The refrigerant tubing and temperature sensor wire were pulled through the hole and the cold plate
was installed. The hole was sealed with spray foam.
The cockpit locker directly aft of the ice box was selected as the location for the compressor. A small
shelf was need to provide a level surface for the compressor. The shelf and cleats were made and
painted. A bubble level was used to set the cleat on the bulkhead. Note the black line at the top of the cleat.
Restrictions above the shelf required use of my handy GearWrench micro ratchet to attach the shelf
to the cleat. The open shelf design with leg allow the tubing and temperature sensor wire to pass beneath.
The Isotherm compressor bracket has two spring loaded slide holders which allow for easy placement
and removal of the compressor/ assembly. Note the slides pulled and in the up position. When the
compressor was dropped onto the pins, the slides clamped onto the compressor base locking it into place.
The refrigerant tubing connectors are brass. The threads were lightly coated with TefGel to prevent galling.
The tubes were connected and firmly tightened.The excess tubing was coiled and secured to a wood plate
attached to the compressor bracket. The finished compressor install is shown below.
The electrical supply was next. The Isotherm 3701 specification stated a maximum current draw of 6 amps.
A 15 amp breaker was specified.The operating instructions stated the unit would run approximately 2 hours
to freeze the cold plate.The cable run was about 15-18 feet from the breaker passing through the engine
compartment. Using Blue Sea Systems Circuit Wizard mobile app, the calculated wire size was 10 AWG.
Red/yellow 10 AWG duplex marine safety wire was run to the compressor.A quick review of the breaker
panel supply showed an adequate 6 AWG fused supply. All connections were coated with TefGel.
Upgrade of the existing electrical system was part of the project.The 3701 literature stated an average power
consumption of 0.65 ah for a reasonably insulation box. The Isotherm literature also suggested battery of at
least 75 ah.That equates to a reserve capacity of 180 minutes.The boat had two Group 29 batteries with
210 minutes of reserve capacity. Reserve capacity is defined as the time, in minutes, the battery can discharge
at 25 amps until the voltage reaches about 10.5 volts.Previously, the two batteries were operated individually
as Bank 1 and Bank 2. The two batteries were combined as Bank 2 with 420 minutes reserve.A new Group 24
dedicated start battery was added as Bank 1.
A new box was built for the dedicated start battery under the aft settee seat.This required the boat’s existing
fresh water pump, accumulator and inlet screen to be relocatedand the 26 gallon fresh water flex tank to be
The control panel was mounted conveniently behind and above the ice box.
The underside of the counter top required additional insulation. A cardboard form was made and filled
with pour foam.The box was marked for about 2 inch thickness and cut with my nifty Japanese pull saw.
The resultant foam block was removed from the form, trimmed to fit and glued under the counter top with 3M 5200.
The ice box lid also required additional insulation. See above pic.
This subproject was more involved. There are two ways to create foam filled shapes; 1) shape a foam block
and apply fiberglass or 2) make a fiberglass shell and pour in foam.The latter technique was chosen.
Using a cheap bake pan coated with mold release compound (PVA or poly vinyl alcohol) two epoxy glass shells
were made. Glass cloth was placed in the pan and wetted out with epoxy.When the epoxy was firm, the
shell was trimmed even with the top lip of the pan.
One shell was cut in quarters and used for the corners of the final shell.The middle sections of the other shell
were used to join the corners. The open space was glassed and the shell filled with pour foam. The foam was
cut even with the lip of the shell using a carpenter’s saw.
The shell was sanded, smoothed with putty, painted and glued to the underside of the id with 3M 5200.
A bead of paintable sealant was applied at the joint and the lid underside with new insulation shell was painted
with several coats of Interlux Brightside.