Failing AC control

[whaler23]

Three split units on the boat and the Master Stateroom unit control is starting to fail, I think. The fan speed control doesn't seem to control the speed at all, the fan pretty much does what it wants, speeding up, slowing down, etc... The fan is mounted simply behind the evaporator coil and blows across the coil either cold or hot as I've selected. The evaporator itself works fine. What's the easiest way to diagnose the fan control knob without buying a new one to check... The controller is the three knob non-digital type.

 

[mobilemn1]

Scott,

I would disconnect the fan from the switch and hook fan directly to the proper current. See if the fan fluctuates, up and down, if not reverse engineer and check with voltmeter to see if the output from the switch fluctuates. then check source of power to the switch

 

[rwetherington]

disconnect the fan from thermostat and take a volt meter, conect to the switch and see if the thermostat will vary the volt to the fan from input voltage down and then back up (120 to 90 volts) if so the motor is the problem but more than likely it is the fan speed control. You can replace just the fan speed control if that is the problem.