99 F250 Superduty Crewcab, V10. Heater stuck on hot. Fan works fine and I can direct the hot air to the correct areas (floor, vents, defrost). I've been through the forums and was pretty sure I needed a new Blend Door Actuator. Pulled the actuator off and put a 1/4" socket extension into the top of the blend door. It moves freely. While the blend door actuator was out, I moved the temperature control rheostat, but the actuator didn't move. Pulled the **** on the rheostat temp controller and it was fine. I'd like to test the rheostat but I don’t know how to pull it out. I guess I could jury rig a couple of connectors, or put pins through the wires, but if it’s easy to remove, I would rather do that. I purchased a used Actuator on ebay and it doesn’t work either (connectors were GREEN with corrosion, cleaning didn’t help). At the actuator there are five wires. I get 12V. across two of them, but don’t know what else I am looking for. Could really use some help trying to figure this out. The dealer wants a lot of money for a new actuator, hench the used ebay part. I've messaged the "partsguyed" and I'm waiting for a reply. Forgot to mention, I check the fuse that protects the blend door actuator, it's fine. I also check ALL of the fuses inside the cab.
I CAN redirect the air, but the air is stuck on hot. It's my understanding that the blend door controls whether heat enters the cab or not. I'm also pretty sure that vacuum controls the valve(s) that directs the air. The blend door actuator is not working. Am I wrong?
You're on the right track. I've attached two diagrams. The wiring diagrams will show which wires are the variable resistor, power and ground going to the blend door actuator. The second one is the plug diagram.
This should allow you to test the variable resistor from the blend door plug, and make sure it's getting power and ground properly.
That was fun and telling, here are the results.
Tested from wiper to one side of rheostat - Nice even resistance change from 17 ohm to 5000 ohm.
Tested from wiper to other side of rheostat - 5000 ohm to 17 ohm.
Tested from Voltage in Run (hot) to Ground - 12V with key on.
This tells me the rheostat is functioning properly and that I am getting the required voltage.
Since the actuator isn't moving - it is faulty, both my original AND the one I purchased on ebay.
Now - I think I can test the actuator by connecting 12V to "Voltage in Run" Ground to Ground and connecting a jumper across wiper to either side of the connection that would go to the other side of the rheostat, but just to be sure, I am going to dig up a rheostat and connect it properly.
Will post back.
Bottom line is, I need WORKING blend door actuator.
It was the Actuator all along.
I found an after market one available from O'Reilly's. Once I had the part number, I was also able to find it on Amazon for less. But since I wanted it today, I paid the extra $8. Total came to about $39. Cool! I paid more than that for the used one that doesn't work on eBay!!
Anyway, moral of the story is, test the wiring if you know how. If not, send me a private message and I will tell you how.
Symptoms are - Fans works fine, you can direct the air to the various vents, but the temp control has no effect. It can be stuck on Hot, or Cold, or somewhere in between. More than likely, if you experience the above symptoms, you have a bad Blend Door Actuator (a small motor assembly used to turn a door open or closed, which isolates your heater core). You may also have a broken Blend Door or shaft going to the blend door. Fixing a Broken Blend Door is a big job. I found a company that claims to have a easier fix here - Heater Treater: Blend Door Fix, Heat and A/C Replacement Parts
I still have not tested if the plug is even getting 12 volts, but from the looks of things I dont see how it could be anything else BUT an internal issue in the actuator motor itself. Going to go test it with 12 volt first.