Mazda MX-5 1990 Workshop Manual page 763

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HEATER
Disassembly I Assembly
Disassemble and assemble as shown in the figure.
1. Heater core
2. Temperature blend door
U-20
3. Airflow mode door
Inspection
Heater core
1. Check the heater core fins for blockage.
2. If the fins are clogged, clean them.
05UOUX-034
3. Check the fittings for cracks or other damage. Replace the
heater core if necessary.