Here's why:
* Resistor Pack Functionality: The resistor pack is essentially a variable resistor that reduces the voltage going to the blower motor. Each speed setting corresponds to a different resistance value, allowing for varying levels of power to the motor and thus different speeds. If the resistor pack fails, it often defaults to the highest setting (full voltage to the motor) because that setting bypasses the resistor entirely.
* Common Failure Point: Resistor packs are prone to overheating and failure, especially with age. The constant cycling of power and the heat generated by the resistor contribute to this.
* Other Possibilities (Less Likely): While less probable, other possibilities include:
* Blower Motor Issues: A failing blower motor itself *could* cause this, though it's less common for it to work at all on high but not lower speeds. A failing motor would likely be completely unresponsive or noisy.
* Wiring Problem: A break or short in the wiring to the lower speed settings could also cause this. This is less likely than a resistor pack issue.
* Control Module Problem: Although rare, the control module for the climate system could have a fault affecting the rear blower specifically. This is a far less likely scenario than a resistor pack problem.
Recommendation:
The most likely and easiest fix is replacing the rear blower motor resistor. You can find replacement parts online or at auto parts stores. It's a relatively inexpensive and straightforward repair (although access to it might vary depending on your vehicle's design – you might need to remove some trim panels to reach it). Many online tutorials show how to replace this part for a Chrysler Town & Country.
If replacing the resistor pack doesn't solve the problem, then you should consider investigating the other, less likely causes mentioned above. A mechanic can diagnose these more complex issues. But start with the resistor pack; it's the most probable culprit.
