Boat air conditioning

10/27/2008

In my first marine Air Conditioning Blues, I said that problems with marine air conditioning systems were water problems about 98% of the time. But as always, I have to eat my words. When we placed the Patricia Ann on the hill this past summer to get her boat blister problem resolved, I knew all of her systems would not work as they had when she was dry-docked.

When we launched her in early September, I could not get the aft air conditioning to switch from heat to air conditioning. Some trouble shooting led me to believe it must be the thermostat. A quick call to a supplier of Marine Air and Crusair Air air conditioning systems, Wayne Wright of Wright Marine and consultation of a book How to Keep You Cool written by Brian, the boat AC guy, confirmed my suspicions. I went ahead and purchased a new thermostat from him just to be on the safe side.

I urge you to check out the book at its website too, it will answer many questions you may have about marine air systems. It's well worth the money!

So what happened? Used trawlers, sailboats and cruisers of the 1980s and 90s era most likely have MarineAir systems aboard. They they were very popular back then and still are for that matter. All of those era systems have mechanical rotary controls aboard. Many marine technicians will tell you they are still more reliable than the newer fancy digital controls.

But when those rotary marine thermostats go unused for long periods of time, they may "lock" in the air conditioning mode or the heat mode depending on the prevailing temperatures. When this happens, your systems sends only a single command to the unit telling it how to work. You can turn the control and not hear the distinctive "click" of the thermostat telling the compressor to heat or cool. The thermostat is "locked" in one of its two modes.

The remedy on MarineAir systems is rather simple actually. On the top photo to the right, you can see the control panel; the thermostat is the knob to the far right. The remedy is to simply recalibrate the thermostat.

Before you attempt this, turn off the power!

Remove the 3-knob panel from the wall and look on the top of the thermostat. Remove the metal plate shown in the bottom photo. A small red screw is located on the back over the coil. The bottom photo shows it in detail.

You simply turn the red screw clockwise until it clicks, then check your control knob turning all the way clockwise and counterclockwise to make sure it clicks two times as you turn it. Ideally you want to have the control knob centered. You now can select either air conditioning or heat.

Have some one turn the power back on and turn on the system to make sure no further adjustments are necessary before you put it all back together. Of course, turn off the power before you begin reassembly.

I got my air conditioning back to normal with this simple procedure.