Air Gauges - E4500

Questions have been asked concerning the operation of the air gauges on the E4500 coach. One of the situations that causes the most confusion is when the gauges read "0", yet a manual gauge shows 160+ psi.

Located in the front junction panel are two pressure "transducers". The function of these components is to convert the coach air pressure in the two brake tanks into a voltage signal. The higher the air pressure, the higher the voltage. The Vansco electrical modules are programmed to use this voltage signal to operate the air gauges on the dash. As the voltage signal increases, the modules "talk" to the instrument panel, telling the gauges to display more air pressure. If the voltage signal decreases, the gauges drop accordingly.

If the voltage signal is less than 1 volt or more than 11 volts, the modules interpret this as a faulty signal and the gauges go to 0 psi. When the coach air pressure rises above 150 psi, the voltage signal will go above the 11-volt limit, causing the gauges to drop to 0 psi.

To troubleshoot this situation, follow the steps listed below:

  1. Pump the brake pedal several times to reduce the air pressure in the brake tanks.
  2. Start the engine.
  3. Watch the air gauges as the air pressure increases.

If the gauges climb to 150 psi before dropping to zero, then the problem isn't the gauges; the air governor that is mounted to the compressor isn't controlling air pressure properly. Check for the following conditions:

The procedure for setting the air governor is found in the MCI maintenance manual under Section 4.

If you need further assistance, contact the MCI Customer Support Center at (800) 241-2947.


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