[Maddog 308]

2000 F350 DRW 7.3L : HELP!
Heater just started blowing cold air regardless of the temp setting. I've replaced the thermostat and coolant in an attempt to fix it - NOT fixed, no difference!
Blows cold then hot then cold then hot regardless of where the temp dial is set and no correlation to speed / revs.
Truck warms up as normal and temp gauge reads normal.
Is there a vacuum line that works a valve that directs the coolant to the heater box or works a flap that directs air to the heater box??

thanks guys!

 

[RT]

Not vacuum - the blend door is controlled by an electric servo motor. Take out your glove box and you'll see it right on top of the heater box. You can turn the vehicle on and adjust the temperature control back and forth and see if its reacting.

 

[Maddog 308]

Thanks much! Should it be the servo on the Blend Door is that an individual part or would I have the Heater box??
Thanks again!

 

[RT]

It's an individual part. Very inexpensive.

 

[Maddog 308]

Thanks RT!!! Very much appreciated!
I'll dive into it tomorrow.