Leaking coolant from rear heater core in my astro van

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.

Rear heater core or line running to the rear heater core

remove the inside trim panels on the left hand side. Most "snap" into place, but look for screws first before pulling on the panel edges.

If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.
When a heater core leaks, a new heater core is installed or the old one repaired.
Heater Housing

• The heater housing is usually under the dash and must be removed to gain access to the heater core.
• Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.

The heater housing is disassembled to get to the heater core. Heater Core

• Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
• Remove the heater coolant hoses.
• Remove the cable and/or vacuum control lines (if equipped).
• Remove the heater core securing brackets and/or clamps.
• Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
• To reinstall the heater core, reverse the removal steps.

When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.

You have a bad heater core it is located in the passenger side dash module , and it will fog the windshield with a film of coolant

Yes!

the problem is probably the heater core, it can become clogged with dribris. this stops heat from the engine getting to it and then no heat.

It sounds to me that you may have 2 problems. 1). Air Lock in the Heater Core. 2). Inactive Heat Damper in the Plenum.

But since you state that the Heater Hoses do not get warm that is indicative of an Air Lock in the Heater Core. This is a relatively simple fix. It is best performed COLD but requires a method of pressurizing the Cooling System. All reputable Auto Parts stores Sell and/or Rent Pumps that temporarily replace the Radiator Pressure Cap for Leak tests and curing Air Lock. The Collant Level must be filled FULL then pressurized and then loosening the Highest Heater Hose at the Firewall so that Air and a Small Amount of Coolant escapes. Once all the Air has escaped tighten the Heater Hose Clamp, remove the Pressure Pump, Restore the Collant Level to FULL, re-install the Pressure Cap and Start the Engine. As it Warms up you should be able to feel coolant running through the Heater Hoses and they should become warm.

Could be a bad heater core, any fluid leaking around it...check under the carpet and padding if you don't see anything under it on the ground. Your coolant may also be low, and it isn't circulating to the heater core, or a vacuum line may be off the hot/cold gate on the heater box, there are a lot of possible causes, but i would check for leaks and fluid level first

SOUNDS AS THOUGH THE HEATER CORE IS PLUGGED. TRY BACK FLUSHING IT AGAIN. IF YOU STILL GET NO FLOW IT IS MORE THAN LIKELY PLUGGED AND WILL NEED TO BE REPLACED. THE TUBES ARE VERY SMALL AND PLUG EASILY WITH RUST.