Air Conditioning Control Electrical Checks:

CONTROL PANEL FEEDS (perform these checks first)

Refer to Page 48 of the 1989 Medallion ETM for wiring diagrams.

1. Check for 12 volts (battery voltage) at pin A1 at the heater A/C module (control panel) connector C273. This is the main feed for the control panel. If voltage is not present, check the dome/clock fuse and the wiring from the fuse to the control panel.
2. Check pin A5 at the C273 connector. There should be battery voltage present with the ignition switch in the run position. If voltage is not present, check the blower fuse and wiring to the control panel.

3. Check continuity from pin B1 and A4 at connector C273 to ground. Both should have continuity to ground.

COMPONENT ELECTRICAL CHECKS

1. Recirculating air door: With a voltmeter across pins A1 and A3 at connector C480 (motor connector), check for battery voltage when requesting "MAX AIR" or "OFF". The voltage will be present for 15 seconds each time a request is made. If the voltage is not present, repeat the check at the control panel at pins A1 and A2. If there is no output at the control panel, replace the control panel.

2. Blend air door: With a voltmeter across pins A1 and A3 at connector C453, there should be 12 volts present when the temperature slide control is moved. If the voltage is not present, check for voltage at the control panel and check continuity of the wires between the control panel and motor. Replace the control panel if the voltage cannot be obtained. If the voltage is present and the motor does not move, replace the motor. The motor also contains a potentiometer to provide the module with information on door position. To check the potentiometer connect a voltmeter across pins B1 and B3 at connector C453. There should be 12 volts present when any of the control buttons except OFF are pushed. If the voltage is not present, replace the control panel. Connect the voltmeter between pins B2 and B3 at connector C453. The voltage should be between 2 and 5 volts, depending on the position of the door and should vary when the temperature slide is moved. If the voltages cannot be obtained, replace the control panel. If the voltage is present but the motor will not move, replace the motor.

3. Air distribution door: Connect a voltmeter between pins A1 and A3 at connector C454. There should be 12 volts present when a mode change is requested. If the voltage is not present. Check continuity of the wires between the motor and the control panel (C487). If the wires are good, replace the control panel. If voltage is present and the motor does not move, replace the motor. The motor also contains a position switch. With a voltmeter connected between pins B1 and B3 at connector C454 there should be 5 volts present. If the voltage is not present, replace the control panel.

4. Blower motor controls: With a voltmeter between pin B1 at the control panel (C487) and ground there should be 12 volts present. If the voltage is not present, replace the control panel. If the blower still does not work, check the wiring between pin B1 and the blower control relay, check the relay and check the wiring between the relay and pin B5 at the control panel (C487). With a voltmeter across pins B1 and B5 at the control panel (C487), there should be 12 volts present whenever the system is turned on. If the voltage is not present, replace the control panel.
With a voltmeter between pin B5 at the blower control module, connector C452 and ground there should be 12 volts present whenever the system is turned on. If the voltage is not present, check the heater A/C fuse, the blower relay and the continuity of the wires between the blower speed control module, the relay and the fuse panel. Check continuity of the wires from pins A4 and B4 at the blower control module to ground. If a good ground is not present, repair open wires. Check continuity of the 4 wires that run from the blower control module to the heater A/C control panel. If the wires are good, replace the blower control module. If the blower still does not work, replace the heater A/C control panel.

5. Compressor circuit: With the A/C on and a voltmeter connected between pin B4 at the control panel (C487) and ground, there should be 12 volts present. If voltage is not present, there is an open circuit in the compressor relay, the thermostat switch, the A/C cutout relay or the wiring from pin B1 at the control panel (C487). If no problems are found with any of these components and the compressor will not function, check for voltage at pin B3 at the control panel (C490). There should be 12 volts when A/C is requested. If voltage is not present, and all the preceding steps check good, replace the control panel. If voltage is present, check the wiring from pin B3 (C490) to the three way pressure switch, check the three way pressure switch and the wiring from the switch to the compressor.