Where are the vacuum lines on a 98 dodge diesel for heat control system?

The 1998 Dodge Cummins diesel's heat control system doesn't rely on vacuum lines in the same way a gasoline engine might. The heat control is primarily managed by a blend door actuator controlled by the climate control system's computer. There might be *some* vacuum lines related to things like the HVAC system's mode selector (defrost, vent, floor) but these aren't directly for *heat* control. They control *where* the heated air goes, not whether it's heated. The actual heat is regulated by coolant flow through the heater core, controlled by a thermostat and the engine's cooling system.

Therefore, looking for vacuum lines specifically for heat control will likely be unproductive. If you're having heat problems, focus on:

* Coolant level and condition: Low coolant or a coolant leak will drastically affect heat.

* Heater core: A clogged or leaking heater core prevents hot coolant from reaching the cabin.

* Thermostat: A stuck closed thermostat will prevent coolant from circulating properly, limiting heat.

* Blend door actuator: A malfunctioning blend door actuator might not allow hot air to reach the vents, even if the coolant is hot. This is more likely the source of your problem than vacuum lines.

* HVAC control module: The computer controlling the climate system itself could be faulty.

In short, while there might be vacuum lines *near* the HVAC system, they're not the primary mechanism for regulating heat. Your troubleshooting should focus on the coolant system and the blend door/actuator.