* Control Panel/Switch Issues: The main culprit is often the climate control panel itself. A faulty switch, a broken connection within the panel, or a malfunctioning resistor pack (which controls blower speed) could prevent certain functions from working correctly even if the blower motor itself is fine.
* Wiring Problems: A short, a break, or corrosion in the wiring harness connecting the control panel to the actuators (the motors that control the blend doors for heat/AC) or the blower motor resistor could interrupt the signal. This is particularly likely in an older vehicle. Check for any visible damage to the wires, especially near the control panel and under the dash.
* Actuator Motors (Blend Doors): These small motors control the direction of the air (heat, AC, defrost, etc.). A faulty actuator can prevent air from going to the desired location even if the blower and controls are functioning. You might feel air blowing but not in the correct direction (e.g., blower on high, but no heat).
* Temperature Sensor: A malfunctioning temperature sensor could lead to incorrect readings, preventing the system from delivering the correct temperature of air.
* Vacuum Leaks (if applicable): Some older climate control systems use vacuum lines to control the blend doors. Leaks in these lines can cause erratic behavior or a complete failure of certain functions.
* Resistor Pack (Blower Motor): While you mentioned the blower works, a faulty resistor pack can cause problems with blower speed selection. While it might work on one speed, others might be inoperative. It's worth checking again, even if the blower is working on one setting.
* Grounding Issue: A poor electrical ground somewhere in the system can cause intermittent or complete failures of components.
Troubleshooting Steps:
1. Visually inspect the wiring: Carefully examine all wiring related to the climate control system for any obvious damage or corrosion.
2. Check the climate control panel itself: Look for any signs of damage or loose connections on the panel. Try gently wiggling the controls to see if that affects anything.
3. Access the blend door actuators: This usually requires removing some parts of the dashboard. You can check to see if they're moving freely.
4. Test the temperature sensor: This requires a multimeter and some knowledge of automotive electrical systems.
5. Check vacuum lines (if applicable): Inspect the vacuum lines for leaks and ensure they're properly connected.
6. Get a professional opinion: If you're not comfortable tackling electrical or mechanical repairs, take the vehicle to a qualified mechanic specializing in older vehicles.
Because you've already checked the fuses, focusing on the control system, wiring, and actuators is the most logical next step. Remember safety first, disconnect the battery before doing any electrical work.
