Im having a problem with my heater, while im accelerating up to speed my heater fan is blowing at full speed. Seems like once im in overdrive the heater will kick down a speed on its own. Sometimes it kicks back into high speed, almost like its surging but this is at random. Most of the time it just seems to run at a slower speed, not enough to keep the cab very warm at highway speed. I have also noticed that when it drops in speed the head lights seem to flicker (just dim for a second).
Im not sure if this is some sort of resistor problem or an alternator problem. My truck is a 2003 f250 v-10 4x4, i dont have fancy climate control or anything just a simple dial.
Hope to hear from someone soon as i dont know where to start
thank you.

 

You have a vacuum leak.

The heating system is vacuum operated. If there is insufficient vacuum to operate the system the default is full fan and to blow out the defroster vents. It happens mostly when you accelerate, which is a low vacuum condition in a gasoline engine.

The first place I would look is at your front 4x4 hubs, assuming you have ESOF.

 

thank you i will check that out...........well i just ran outside in the cold and looked at the passenger side vacuum hose to the hub. there is an elbow with a small plastic hose joiner that runs through a small metal plate and the plastic piece is broke completly in half. thank you redford i think you have saved me alot of money, i was thinking it was something electrical.

 

My 2006 4x4 F-250 Super Cab 6.0 liter Diesel suddenly today experienced the Heater Fan on High Speed all the time. It doesn't make any difference if the A/C is turned On, or Off. I select the Fan to low, but the Fan still runs on High Speed all the time, even though the display shows that Lo is selected. I can turn the unit OFF, or select any source but the Fan still is in High Speed. Looking for suggestions. I believe that the unit may be vacuum controlled, but I am not sure where the source is located.

 

You have the blower motor relay problem...If you have the manual type then the relay is on top of the motor.

 

Thanks, I will try to dig the information up. I have the digital unit, meaning that I can select the temperature that I want, and it will adjust to that temperature. In the Auto position, the fan speed will adjust automatically to provide the requested airflow and temperature. I have pulled the Glove Box Door out of the way to see the Heater, so hopefully will be able to locate and isolate the defective part.

 

Well with the EATC system the relay is more of a resistor with a diode.

It will not be on the blower motor. Rather should be against the firewall, on the side of the evap housing.

Look at this:
Ford EATC Blower Motor Speed Controller

Will be something like this. Replace that and you should be ok.

 

Thanks, I will look for it shortly. I really appreciate this. I am glad that when I bought the truck that I required them to throw in the complete manuals for all systems. It helps a lot when troubleshooting.

 

$69.95 for the part and she is back in action. Thanks for the help.

 

Glad it worked...

 

I recently had the heater stop blowing hot air on my '05 F350 Diesel. I think its the Blend door, but can't for the life of me figure out how to get it out to repair the gear. Is this something that requires the entire Dash be disassembled, or should I be able to get it done through the glove compartment area. Any help or suggestions(pics would be great) on how to proceed would be awesome.

 

gonna have to go at in from the dash. I would have to look but the airbox may come apart under the glove box.

 

I have a problem which started yesterday with my 2004 F350 Lariat with the 6.0 diesel. When I started the truck yesterday morning everything was fine - it was raining and I had the defroster on. I started the truck after work and it was warm enough that I wanted the A/C on. I switched the heater control to A/C and cranked the fan up but nothing happened. I tried moving the fan switch and the heater controls and it made no difference.

I opened the windows and started home figuring I would look at the fuse panel when I got home. About 15 minutes after the truck was started I came to a stop in traffic and I noticed that there was now cool air blowing from the vents. I cranked the fan to the max and had air flow but it did not seem to be as fast as usual on high speed. I closed the windows and noticed that the longer I drove, the faster the fan seemed to blow.

When I left for work this morning the fan was working but when I left work this evening again I had no fan. I left the fan on high speed and after about 10 minutes the fan started to blow. Does anyone have any suggestions as to what the problem may be?