Kneeling System/Electrical - D Series Coaches

In Section 12, we discuss the Kneeling System/Air Flow - D Series Coaches. This service tip will deal with the electrical portion of this feature. As a suggestion, print out both the November and December service tips and reference them at the same time.

The kneeling feature electrical is addressed in four separate stages; normal operation, bump up, kneeling, and recovery. This will coincide with the discussion of the air portion of the feature.

Kneeling System Electrical – Normal Operation

While the coach is at normal ride height, none of the circuits for the kneeling system are active. As air pressure increases in the coach, pressure switch PS4, located at the accessory tank in the lower drag link compartment, closes supplying 24 volts to stud 5 in the kneeling junction box which is located in the #1 LH baggage compartment. When the park brake is applied, kneeling relay R1, located in the front electrical junction box, is energized supplying 24 volts to both the interior and exterior kneel switches. See Figure 1 (click to enlarge*).

Figure 1

Kneeling System Electrical - Bump Up Stage

Pressing either kneel switch supplies 24 volts to stud 63 in the front electrical junction box and to stud 2 in the kneeling junction box. Power at stud 2 continues to pin B+ on the kneeling box latching relay RL1. While the entrance door is closed, ground is connected to the opposite end of the latch coil and the relay is switched to the latch position. Twenty four volt power flows from stud 5 through the RL1 relay, energizing stud 6.

Power from stud 6 energizes the R2 relay, supplying 24 volts to the red wire and ground to the black wire on SOL2. This closes SOL2, separating the LH leveling valve from the double check valves. SOL2 also exhausts all air pressure out of the line routed from SOL2 to the double check valves.

Power from stud 6 also flows through the PS1 switch, energizing SOL1, which causes the front suspension to rise momentarily (bump up). See Figure 2 (click to enlarge*).

Figure 2

Kneeling System Electrical - Kneeling Stage

The PS1 switch is connected to the air line exhausted by SOL2 so it only stays closed momentarily after the kneel switch is depressed. When the PS1 switch is opened, SOL1 is de-energized, allowing air to exhaust out of the front bellows, which causes the coach to kneel. See Figure 3 (click to enlarge*).

Figure 3

Kneeling System Electrical - Recover Stage

When the coach is in the kneel position, the PS3 switch is closed, allowing power to route from stud 5 to the PS2 switch and also to pin 1 of the kneeling box relay R1.

The PS2 switch is a normally closed pressure switch, pre-adjusted to 50 psi and connected to the front air bellows. At normal ride, this switch is open because the bellow pressure is greater than the setting, but when the coach is knelt, the PS2 switch is closed. Power from the PS3 switch routes through the PS2 switch to pin 7 of the kneeling box relay R1, energizing the relay. Power from pin 1 flows through the relay to pin 7 of the kneeling box latching relay RL1. See Figure 4 (click to enlarge*).

Figure 4

When the recovery switch is pressed, stud 64 in the front box and stud 1 in the kneeling box are grounded. Also grounded is the A- pin on the RL1 kneeling box latching relay, resetting the relay. With the relay reset, power routes through to pin 1 of the kneeling box latching relay. Power flows in two directions; through the diode jumper to stud 6 of the kneeling box stud bar and down circuit 1-BK, bypassing PS1 switch energizing SOL1. See Figure 5 (click to enlarge*).

Figure 5

As air pressure increases in the front air bellows, the PS2 switch opens. Power that was originally routed through the switch is disconnected, but because of the configuration of jumpers on the kneeling box relay R1, the relay stays energized (PS2 also controls the external light and audible alarm, not shown). See Figure 6 (click to enlarge*).

Figure 6

When the coach ride height reaches approximately 10", the RH leveling valve removes the air pressure signal routed to PS3, opening PS3, which removes power to the kneeling box relay R1. SOL1 is de-energized, shutting off the quick recovery. Kneeling box relay R2 is also de-energized, causing power and ground to be reversed to SOL2. The LH leveling valve is now reconnected to the air bellows and air supplied through the leveling valve raises the front suspension up to the factory setting of 11". See Figure 7 (click to enlarge*).

Figure 7

If the park brake is released while the coach is in the kneel position, the kneeling box relay R3 located in the front electrical junction box is de-energized, supplying a ground connection to stud 64 in the front electrical junction box. This activates the recovery stage the same as if one of the recovery switches were pressed. See Figure 8 (click to enlarge*).

Figure 8

For further assistance, please contact the MCI Customer Support Center at (800) 241-2947.

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