Where is the check valve to heater control on a 1998 dodge ram 1500?

There isn't a single, easily identifiable "check valve to heater control" in the way you might be thinking on a 1998 Dodge Ram 1500's heater system. The flow of coolant to the heater core is controlled by a blend door (or a valve operated by a blend door actuator) inside the HVAC housing, not a check valve in the traditional sense of a one-way valve.

The system relies on the blend door to regulate hot and cold air mixing. If you're having issues with your heater, the problem is much more likely to be:

* Blend door actuator: This motor moves the blend door to control the amount of hot coolant flowing to the heater core. A malfunctioning actuator is a common cause of heater problems.

* Blend door: The door itself might be broken or jammed.

* Heater core: The heater core itself could be clogged or leaking.

* Thermostat: A faulty thermostat can prevent the engine from reaching proper operating temperature, impacting heater performance.

* Coolant level: Low coolant means less available to heat the heater core.

* Water pump: A weak or failing water pump won't circulate coolant effectively.

To diagnose your heater problem, it's best to start by checking the obvious things (coolant level, thermostat), then investigate the blend door actuator and potentially the heater core. You'll likely need a repair manual specific to your 1998 Dodge Ram 1500 to access and diagnose these components. Accessing the HVAC system generally requires removing parts of the dashboard.