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Electrical Components Troubleshooting

1.  If the amount of air delivered by the blower is insufficient and the blower is inoperative, check the following:

A) Blown fuse or faulty circuit breaker

B) Battery voltage low

C) Disconnected or shorted wire

D) Faulty motor ground (the motor is grounded inside the evaporator/heater box, and therefore the box also must be grounded to the frame)

E) Faulty motor or blower switch

2. If the blower is inoperative only on high speed, these items should be checked.

A) Faulty high-speed blower fuse

B) Poor ground to high-speed relay

C) Defective relay

3. If the blower motor will only operate on high speed, then a bad resistor is the likely cause.

4. If the blower motor operates sporadically, the following could be the cause:

A) A loose or shorted wire

B) An overheating or faulty circuit breaker

5. Excessive blower vibration can almost always be traced to debris such as paper, cellophane, etc., being sucked up into the blower wheel via the return air door. Occasionally, a blower wheel on the motor shaft may be broken or may have come loose.

6. If the blower is only delivering air to the windshield check for:

A) A disconnected vacuum hose

B) A cracked or missing plug on the back of the control head

C) A defrost door that is binding

D) A faulty vacuum servo - a rare occurrence. (Most diesel coaches will have an electric motor driven vacuum pump which additionally supplies the vacuum for the cruise control and vacuum step if so equipped.)

7. If the blower functions normally with insufficient air supplied, check for:

A) Disconnected duct hose

B) Evaporator freeze-up due to faulty thermostat or high humidity, and thermostat settings preventing the compressor from cycling on and off

C) A faulty control head selector switch