| Author | Message | ||
     Griffmeister |
Since the Quick Board has been used as a kind of knowledge vault, and I'm freezing my a$$ off, I'd thought I'd give it a try. My current work truck is an '02 F550 Super Duty. The heater has been very temperamental, more off than on. You can feel both hoses going through the firewall getting hot, so the core has heat, but for some reason the various duct doors don't work properly. Our vehicle mechanic changed the switches and it worked for about a week. Then one day it stuck on full heat, which was nice until the engine was fully warmed, then it got pretty oppressive. When I left the job, the damned thing was stuck on cold and has been since. Anyone know how the doors are supposed to work? I wonder if I could just wire the right one partway open (kind of like my exhaust actuator). | ||
| Thumper74 |
I'm going to work on the assumption that the thermostat is okay, it's running at normal temps, etc. No heat at all, or is it only coming from one vent? If no heat, look at the blend door actuator. It's what 'mixes' the air to the correct temperature. If only one vent, floor, dash, etc. look at the mode door actuator. Usually, as a safety feature, the mode door actuator will default to defrost mode in the event of a failure. The blend door actuator on your truck, should be electric, not vacuum operated. It's right behind the glovebox. If you open the glove box, you should be able to access it and hear it working as you change the temperature. If you dont, use your handy dandy multimeter and check for variable voltage at the actuator as you change the temp on the dash. If the voltage changes, but the door doesn't work, replacing the actuator is a safe-ish bet. If there is no voltage change at the actuator, start chasing wires and checking the control head. The mode door actuator is vacuum, so it would be pretty easy to check as well, but it sounds like a blend door issue. | ||
| Etennuly |
The heater core is behind the glove box. Pop out the glove box and there it is. One of the easiest to get to that I have seen. Just warm up the truck and activate the heater controls while watching what is happening in that area. You should see arms mounted to the air box doors moving(or not). I don't recall for sure but I think some of the diesel trucks use electric actuators. There is a good chance that leaves, dirt, or other debris has piled up in the way of the door's movement. The heater core can be removed easily to clean out the box also. | ||
| Thumper74 |
The only that should be right there is the blend door actuator and it's electric. All the others are vacuum. I was looking at the service manual. I'd put money on a dead blend door actuator. | ||
| Griffmeister |
Thumper, you describe it perfectly. Yeah, operating temp of the engine is good, core warm but no heat out of any of the vents. Being behind the glove box is a plus. The only thing that scares me now is that there are some electrical gremlins behind the dash so I hope that's not what's affecting the blend door. Thanks for the info. |
