It's cold out.
I hop into the 2004 3500, cummins.
Start her up, set the temp, no heat?
After 5 or 10 minutes, still no heat.
I turn the fan off and shut the temp.
Reset heat and turn fan on, I hear I door slap, now I have heat?
All other functions work fine.
I assume it's an actuator that controls the heat level?
How do I isolate which actuator is at fault?
Thanks for any suggestions.
Mike from Banff, Alberta

 

Most likely, the actuators are fine. The doors inside of the HVAC box that control the movement and blending of air are notorious for failing. The doors and guide pins commonly break and the foam breaks down which makes air flow/control ineffective.

Check out the link below. Check out the installation instructions and some of the instructional pages:

https://www.blenddoorusa.com/collect...l-complete-kit

Due to a leaking heater core, I pulled my HVAC box and rebuilt my HVAC box with a full set of new Blend Door USA parts. Big job.

Here is what a bad door looks like. Note the cracked guide pin, door hinge, and bad foam:



Here's a pic of the box with rebuilt components.





The dash needs to be removed to pull to the HVAC box...

 

I just noticed how old the original post is. Hopefully it helps others in the future...