2003 Honda odyssey heater not working sometimes hot then warm then cooler air. Changed thermostat , flushed system, even bypassed the water bypass. Just doesn't seem like the water is flowing through the heater hoses like it should . Van never runs hot so circulating through cooling system just not through heater hoses.

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:

1. 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.
2. Check the coolant level in the radiator. If the coolant level is low, the heater may not be able to produce hot air.
3. Check for any leaks in the coolant system. If the system is leaking, it may not have enough coolant to produce hot air.
4. 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.

Most ductwork doors are controlled with actuator motors that open or close flap doors. These doors change the amount of heated air that enters the system as well as where it goes such as the floor or defrost. There are probably 6-8 of them on the system. My guess is that one of these actuator motors is not working due to its age.

Most likely it is a clogged heater core. Have your heater core reverse flushed or your blend door is stuck open.

First of all make sure you bleed all the air out properly , air locks can cause the cooling fan not to work . Is the cooling fan working? If all this is ok does the whole system get hot like the radiator and interia heater if not id be looking at the waterpump

may have air trapped in it still or thermostat is not working properly..

You mean turn on heat but get Only cold air ?
Is it front heater work and hot?
If so. The heater hose to the rear core is plug. Need to flush it from both direction and make sure is full of coolant (Water).
You should be good to go.

Mai Lor

Heater core is not working.

If the heater core bypass refers to the water flow to the heater core, I would wonder why you did not flush the heater core as part of the system. You can drain water from engine, disconnect heater hoses and add a short hose to the heater and force a garden hose to flush the core.

I have not looked up the particulars for which heater system is on your car. Some just use duct-work to close off air flow through the heater core and the heater core always has hot water in it. Others will use a valve to shut off the water flow through the heater core and they can be either electric or vacuum operated. Combination systems are the third system which controls water flow and duct air flow at the same time.

Some of the Premium Climate control systems with Electronic displays have a computer diagnostic system which self-diagnoses problems but you need the sequence codes and explanation of where the bad part is located.

change your thermostat. and flush your cooling system.