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Q: Does does a 2004 Volkswagen Passat GLX 4 motion sedan have heater control valve? on 2004 Volkswagen Passat

Repair pal screen says yes, but my dealer service advisor says no. He claims it is direct flow to the heater core, and there is no heater control valve.
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No warm air comes from the heater. It blows only cold air. Garage diagnosed it as a clogged heater core. Windows will fog over.
Does not have a heater control valve.

Customer Concern: The heater is performing poorly and the passenger compartment feels like there is no heat.

Tests/Procedures: 1. Verify blend door operation.

2. With a factory compatible scan tool, enter Address Word 08-Air Conditioning. Select Function 04-Basic Settings. Enter Display Group 000. This is the air distribution flap motor basic setting. The values on the screen will count up then count down and show all "0's" when completed. If there are no fault codes stored at that point, the blend door is operating correctly.

3. Without a factory compatible scan tool, a visual inspection is required to verify blend door operation.

4. For a heater core to operate correctly, the base cooling system must be in proper working order. Be sure to check the following and correct any concerns as needed:

5. The water pump must be intact (not broken or slipping on it's splines) and be circulating the coolant through the system. On these VW/AUDI vehicles, the water pump is actually sucking the coolant through/from the heater core. It is not pushing the coolant through. Disconnecting the heater core hose and looking for flow is not a valid test.

6. The thermostat must be properly rated for the vehicle (most VW/AUDI thermostats start to open at approx. 86*C or 187*F). The thermostat must also not be stuck closed creating an overheat condition or stuck open creating an underheat condition.

7. The condition of the coolant is critical to proper cooling system operation. The factory coolant is G12 and is a non-phosphate/non-silicate based coolant. When factory coolant is intermixed with standard type ethylene/glycol based coolants the chemical reaction starts to solidify and gel up in the cooling system creating restrictions and flow concerns.

8. Proper flow through the cooling system is critical. As a general rule of thumb, the upper coolant return hose to the coolant reservoir is the last hose supplied with coolant. Get the vehicle up to normal operating temperature. At idle, the upper return hose may spit and sputter and little flow will be seen. If the RPM is raised to 3000, there should be a noticeable increase in flow and amount of coolant flowing through that hose. If there is good flow, this is a good indication that the rest of the base (engine) cooling system is free of restrictions and flowing correctly.

9. The radiator must be free of restrictions and flowing freely. Use an infrared thermometer and check the upper and lower hoses for proper temperature difference.

10. The radiator fans must be able to turn on of their own accord. If the fans turn on by themselves, this is a good indication that the radiator is in proper working order.

11. Measure the two heater core hoses at normal operating temperature. With full heat commanded and blower motor on High, I would expect to see roughly a 20-30 degree difference between the hoses. An extremely large difference (60 degrees or so) would indicate a completely plugged heater core that is not allowing flow. A small difference (5 degrees or so) would indicate a partially restricted heater core that is only allowing coolant to flow through a small portion.

12. If the heater core appears to be the cause of concern, backflushing the heater core is an option to try before removing the dash and replacing the heater core. For best results, use a solid detergent that has low foaming and easy rinse characteristics. Dishwasher detergent seems to work the best. Let the heater core soak and use air and water to agitate the heater core when flushing.
Tech Tips: A common characteristic of a partially plugged heater core is varied heat output. If there is good heat while cruising down the road (higher RPM and more flow), but poor heat output at idle (lower RPM and less flow), this strongly indicates that the heater core is restricted causing the concern.

Try to find someone that can back flush the heater core. Replacing the core is quite expensive.
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