1. Check the obvious:
* Fuse/Circuit Breaker: Ensure the fuse or circuit breaker for the blower motor and heater is not blown. Consult your owner's manual to locate the correct fuse/breaker.
* Power to the Blower Motor: With the ignition ON, use a multimeter to test for power at the blower motor connector. You should have battery voltage (12V) at the appropriate terminals when the fan switch is activated. If no power, trace the wiring back from the motor to the switch and fuse/breaker.
* Blower Motor Switch: Make sure the blower motor switch itself is functioning correctly. Try different speed settings. A faulty switch can prevent power from reaching the motor even if the fuse is good. If you can, test the switch's functionality with a multimeter.
* Wiring: Inspect the wiring harness leading to the blower motor for any damage, corrosion, or loose connections. Pay close attention to the connections at both the motor and the switch.
2. Beyond the Blower Motor: Since the blower motor is new and you have power to it, the problem is in the heating system itself:
* Heater Core: The heater core is a small radiator that warms the air blown by the blower motor. It could be clogged, leaking, or even completely blocked. This requires accessing the heater core (usually involves some dashboard disassembly), which can be a significant job. A low coolant level or a leak in the cooling system can also contribute to this.
* Thermostat: A malfunctioning thermostat may prevent coolant from circulating through the heater core, resulting in no heat. A stuck-closed thermostat would prevent coolant flow, while a stuck-open one might only give slightly warm air. A new thermostat is a relatively inexpensive and easy part to replace.
* Water Valve (if equipped): Some vehicles have a water valve that controls the flow of coolant to the heater core. This valve may be stuck closed, preventing hot coolant from reaching the heater core. This valve usually operates via vacuum. Check for vacuum leaks in the lines leading to it.
* Coolant Level: Check your coolant level. Low coolant can prevent the heater core from functioning effectively. Top it off if it's low, but only use the proper coolant mix for your Cadillac (check your owner's manual). A leak in the cooling system needs repair.
* Blend Door Actuator (for temperature control): This controls the blend of hot and cold air. If it's stuck in the cold position, you'll get no heat, regardless of the blower and heater core. This often requires dashboard disassembly to access.
3. Next Steps:
* Visual Inspection: Carefully inspect all visible parts of the heating system, looking for leaks, damaged hoses, or anything out of the ordinary.
* Professional Help: If you're not comfortable working on your car's heating system, it's best to take it to a qualified mechanic. Diagnosing and repairing heating system problems can be complex and time-consuming.
Important Note: Remember to always disconnect the negative battery terminal before starting any electrical work on your vehicle to prevent accidental short circuits. Also, never work on the cooling system while it's hot – allow it to cool completely to avoid burns.
