1997 Dodge Ram; 5.2, 4wd with AC. Heater does not produce a tremendous amount of heat. I have replaced the vacuum hose from the cruise module under the battery to the manifold. All the "heater doors" work correctly, air is blown to the correct vents but the heat control seems ineffective. Sometimes I will feel "resistance" turning the dial as if against air cushion. AC works fine when heat control turned to cold. My gut tells me a vacuum problem somewhere, maybe even the control. My next plan is to trace vacuum from manifold to control and onward. Any suggestions before I start? It is not a thermostat, cooling system or heater core problem.
I need you to let me know if the engine is reaching operating temp, at the gauge. Then also when warm, do both the heater hosed going into the heater core feel warm and close to the same amount of heat. Sounds like you may have a plugged heater core in which I will next ask you to try flushing out the heater core. You can remove the right side (passenger side) heater hose by the manifold and remove the left side heater hose by the water pump. Flush core with garden hose and you should see a steady stream of water coming out the other end of the hose. Also reverse the direction of the flush. Do this for 10 min and hook up the hoses and tell me what you have.
I did flush the heater core when I first discovered the problem. Water flowed freely in both directions and was clean almost instantly. I think it is vacuum related as when I dial the heat control from hi to low or from low to hi I sense a resistance in the movement of the dial. Engine does get to operating temp, actually put in a new thermostat just to make sure.
I need to see if the heater temp cable is moving properly. You may have to remove the heater control head to gain visual on the cable and on the door. Picture below is what the cable will look like and what it is attached too.
Where is the heater control head? I am assuming I will be under the dashboard?
The heater control head is what you adjust when you turn the heater knob. I really want to know if you can just go under your dash and at the same time move the temp mode button and see if you can see the cable move. The cable should be towards the top of the heater box so it might be difficult to see, I just want to eliminate the possibility of a cable that is off the door latch or a door that is broken inside the heater control box.