1996 Ford Aerostar Owner's Manual - Page 92

To set the interval wipers, rotate the knob at the end of the turn signal lever toward or away from the instrument panel to the interval operation you desire. To clean the windshield, push in the end of the wiper knob. For a constant spray, keep the knob pushed in. After you release the knob, the wipers operate for two to three cycles before turning off (if wipers were off) or returning to the selected setting. NOTE: The addition of shields to the front of the vehicle (e.g., bug shields) may adversely affect the windshield washer system from delivering fluid to the windshield. Devices such as bug shields are not recommended for your Ford vehicle. Do not try to clean the windshield when the washer fluid container is empty or activate the washers at any time for more than 15 seconds continuously. This could damage the washer pump system. RWARNING In freezing weather, the washer solution may freeze on the windshield and obscure your vision. Always warm up the windshield with the defroster before you use the washer fluid. If you cannot see through the windshield clearly, it can increase the risk of being involved in a collision. For information about refilling the washer fluid or replacing your windshield wiper blades, see Windshield washer fluid and Wipers in the Index. 111