I believe have either an issue with the blend door motor, or the temperature ****. Here's what's happening:

I can have it on hot and be driving along, then it will start blowing cold air. I can move the temperature switch to cold then back to hot, and it'll start blowing hot air again.

Does anyone know if that would be temp **** or the motor? I don't want to just change parts randomly.

Thanks!

03 F250

 

Do you have manual heater controls?

 

I assume they are manual. There are 3 *****. I didn't know there was anything different than that though.

 

Yes, there are options for automatic temp controls.

 

Can I pull the blend door motor out and plug it up to see if it's turning?

 

Over the weekend I pulled the motor actuator and it seems to be moving just fine. I stuck a 1/4" extension on the top of the heater box, and could turn the blend door fine, everything seemed good there. I put the actuator back in, and turned the temp **** and could hear the motor working.

Here's how it acted last night when I drove it to church. I left the temp **** all the way on hot the whole time. As the truck's temp gauge started to move up a little, it seemed like the air coming out got a slight bit warmer, then it went cold. After the truck got up to operating temperature (gauge in the middle of range), the heater air all of a sudden got hot.
Is there a cutoff valve on the hoses that could be malfunctioning? I've not had a chance to look as it's been pouring the rain here.

 

Maybe, you will have to look at the heater hoses. If there is one, it's intended to be closed only when vacuum is applied to it in the (mode switch) MAX A/C position.

While you're under the hood, check the temps of the two heater hoses. With a fully warmed engine, both hoses should be HOT, in the order of up to 190°F. If you do not have HOT coolant continuously flowing through the heater core loop, you cannot have steady heat, assuming everything else is functioning normally.

I had a similar issue several years ago on my 01 which uses the identical blend door actuator as does your 03. On mine, I found a cracked solder joint on the printed circuit board in the BDA that was making intermittent contact and causing the BDA to move the door to the cold position (in November...). I re-soldered it and it's been fine since.

While I was under there, I did observe that the heater core is right behind a removable panel behind the glovebox. When everything is HOT, that thing will burn your skin (don't ask...) and is a simple location to check (safely, of course) to see if you have HOT coolant flow. Be aware that your 03 might be a bit different from my 01 as there were a few changes between 01 and 02 model years.

 

Thank you! I'll fire it up this evening after work and see what I can figure out and post back.
I don't think it's the blend door moving back to the cold position. When I move the temp ****, there's a distinct sound difference in the moving air between the hold and cold positions.

 

I've started another thread on this issue, since I believe I've ruled out an issue with the blend door or any of those controls. I believe it is circulation related.