Field Testing The Boost Solenoid

At first notice you would tend to think that the only function of the Boost Switch is to boost the engine battery voltage during the main engine start cycle, but, the switch also has a locked “ON” position that allows the house charger to transfer charging voltage to the engine batteries when you don’t have the option of starting and running the main engine for any significant period on a regular basis.

When the boost switch is activated there is a light in the switch that should come on. If the light does not come on when the switch is activated this does not mean that the boost circuit is inoperative, the light is an indicator that the switch is in the “on” position. If the light is out it simply means the switch bulb should be replaced.

Follow the sequence below to check the basic operation of the boost solenoid:

1) Locate the voltage meter in your dash gauge panel. This volt meter indicates the engine battery voltage any time the ignition key is on.

2) Hook coach to shore power

3) Check that the house battery charger is on and charging the house battery, the voltage range of the house batteries while charging will typically be between 13.2 to 14.0 volts, this is indicted on most coaches at the inverter control panel or on the dash monitor screen.

4) With the boost switch in the “off” position, turn the ignition key to “on” without starting the coach.

5) Note the reading of the volt meter on the dash gauges at this point. With fully charged engine batteries the voltage should read in the 12.0 to 12.8 volts range. This reading will be lower if the engine batteries are discharged.

6) With the ignition key remaining in the “on” position activate the boost switch. Watch the voltage on the dash gauge for a few seconds. There should be a noticeable rise on the voltage gauge, if the voltage does rise; the boost circuit is most likely working as it should. If the voltage does not rise and remains static, it could indicate the boost solenoid needs replacement.

If you do suspect a problem in the circuit contact our service department for an appointment and they will be able to confirm there are no other issues in the circuit and determine if the solenoid requires replacement.

To order a solenoid from our parts department contact 1-800-955-6226 option # 3 and they will be able to get you the proper solenoid for your year model coach.

Also, the next time you are in Nacogdoches for service whether you suspect boost system problems or not make sure you ask our service department about having them install a voltage sensitive relay which will allow your system to charge the engine batteries automatically when hooked to shore power or generator. This will eliminate the need for manual boost switch activation, and can be installed on most all year model Foretravel coaches.