Windshield wipers on the E4500 and J4500 coaches are controlled by a single electric motor. The electrical circuit for this motor can be broken up into 4 separate phases; intermittent, low speed, high speed, and park. The key to the correct operation of the wipers is a set of contacts inside the motor itself.
In Figure 1, two motors are disassembled. The motor on the right shows three intact contacts whereas the motor on the left shows contacts that have been damaged. On close inspection, note that the outermost, or "Ground", contact on the left motor is completely missing.
Referring to the motor on the right;
When the wiper motor is running, only two of the three contacts are connected to the metal ring at any time.
Ground for the intermittent relay, the R1, JRE3, & JRE4 relays is provided through the grounding module located in the front junction box.
24V power is provided as follows:
Figure 2 (click image for enlarged printable view*)
Intermittent Phase - Powered. See Figure 3
Figure 3 (click image for enlarged printable view*)
Intermittent Phase - Timer Activated. See Figure 4
REMINDER: If the ground signal is not present on the WM2 circuit, the wipers will not pause; they will continue to operate at low speed. There may be a slight hesitation at the park position, then the wipers resume operation.
Figure 4 (click image for enlarged printable view*)
When the wiper switch is moved to the low speed position, 24V power is routed to the R1 relay, energizing the WM5 (low speed) circuit.
High Speed phase. See Figure 6
When the wiper switch is moved to the High speed position, 24V power is routed to both the R1 relay and the JRE3 relay.
WARNING: THE LOW SPEED AND HIGH SPEED CIRCUITS SHOULD NEVER BE ENERGIZED AT THE SAME TIME. THIS CAUSES THE WIPER MOTOR TO RUN SLOW AND EXTREMELY HOT!
Figure 6 (click image for enlarged printable view*)
Park Phase - Powered. See Figure 7
With the wiper switch in the OFF position, the R1 relay is de-energized connecting the WM5 (low speed) wire to the WM2 circuit. As long as the wipers are positioned anywhere except at the center windshield post, the WM2 wire is connected to 24V.
Figure 7 (click image for enlarged printable view*)Park Phase - Powered. See Figure 8
When the wipers reach the center windshield post, the 24V power supply is removed from the WM2 circuit. The WM2 now is connected to ground and this acts like a brake to prevent the motor from "coasting" through the Park position.
Figure 8 (click image for enlarged printable view*)
If you have any questions, please call the MCI Customer Support Center at (800) 241-2947.
Motor Coach Industries: Corporate Address 200 East Oakton Street, Des Plaines, Illinois 60018 | Phone: 866-MCICOACH
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