I. Safety First:
* Coolant Level: Check your coolant level in the overflow tank. Low coolant can severely restrict heater function or even damage the engine. Add coolant if needed (use the correct 50/50 mix of coolant and distilled water).
* Engine Temperature: Ensure the engine is up to operating temperature. The heater won't work effectively if the engine is cold.
II. Basic Checks:
1. Heater Controls:
* Fan Speed: Try all fan speeds. If the fan doesn't work at any speed, the problem might be with the blower motor, its resistor, or the related wiring.
* Temperature Control: Check the temperature control knob/slider. Try switching between hot and cold. If the control itself is broken, that needs repair/replacement.
* Airflow Direction: Make sure the vents are directing air where you expect. A stuck or broken air direction control could be the issue.
2. Check for Obstructions:
* Air Filter: A clogged cabin air filter can restrict airflow. Locate and replace if dirty.
III. More Advanced Troubleshooting (This often requires a multimeter):
1. Blower Motor:
* Access: Locate the blower motor (usually under the dashboard). This may require removing some panels.
* Visual Inspection: Check for any obvious damage or debris.
* Power Test (Multimeter): With the key on, check for power at the blower motor connector. If there's no power, trace the wiring back to the fuse box. A blown fuse, faulty relay, or a wiring problem could be the culprit.
* Ground Check (Multimeter): Ensure the blower motor has a good ground connection.
* Blower Motor Resistance Test (Multimeter): Disconnect the blower motor and measure the resistance across its terminals. Compare to the specifications found in a repair manual or online. High or infinite resistance indicates a faulty motor.
2. Blower Motor Resistor: This controls fan speeds. It's often located behind or near the blower motor. A failed resistor usually results in only high speed functioning or no fan at all. Test for continuity and correct resistance values with a multimeter (refer to a wiring diagram).
3. Heater Core:
* Coolant Flow: With the engine warm, carefully feel the heater hoses going to and from the heater core (located behind the dashboard). Both hoses should be hot if the coolant is circulating properly. If one is cold, there may be a blockage in the core or a problem with coolant flow. *Note: Be careful; these hoses are hot!*
* Leak Check: Look for evidence of coolant leaks around the heater core. A leaking heater core is a common problem and requires replacement.
4. Thermostat: A faulty thermostat might prevent the engine from reaching operating temperature, restricting hot water to the heater core. A stuck closed thermostat would prevent the engine from heating up.
5. Water Pump: A faulty water pump won't circulate coolant efficiently, affecting heater performance. Check for proper water pump operation. Listen for noise and feel for vibration.
6. Wiring and Connectors: Inspect all wiring and connectors related to the heater system for damage, corrosion, or loose connections.
IV. Repair or Replacement:
Once you've identified the faulty component, replace it. Repairing a heater core is difficult and usually requires professional help, while replacing it may require dashboard disassembly.
V. Resources:
* Repair Manual: A Haynes or Chilton repair manual specific to your 1999 Ford Ranger is invaluable for diagrams, specifications, and troubleshooting steps.
* Online Forums: Search for forums dedicated to Ford Rangers. Other owners may have experienced similar problems and offer solutions.
Disclaimer: Working on your vehicle's heating system can be complex. If you're not comfortable with automotive repair, it's best to consult a qualified mechanic. Improper repairs can lead to further damage or safety hazards.
