There could be a few possible causes for the rear heater not blowing hot air in your 2003 Chevrolet ASTRO van. Here are a few things you could check:
- Make sure that the rear heater control valve is fully open. This valve is located near the heater core and controls the flow of coolant to the rear heater.
- Check the coolant level in the radiator. If the coolant level is low, the heater may not be able to produce hot air.
- Check for any leaks in the coolant system. If the system is leaking, it may not have enough coolant to produce hot air.
- Check the thermostat. If the thermostat is stuck closed, it may not be allowing enough coolant to flow through the system to produce hot air.
If these steps do not help, it is possible that there is a problem with the heater core itself, or with other components of the heating system. It may be necessary to have a mechanic diagnose and repair the issue.
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