I have a 2012 f250 xl gas 6.2 truck that has had hvac problems since I bought it a couple years ago. The vents in the dash cannot be turned off without closing them (at the grills outside of dash)by hand (no matter if using heat, ac or vent) I thought it might be the electronic control in the dash so I replaced it with a used unit but still same problem. Also, when I am using ac and stop for gas or a short period, when I start truck again the heat comes on for a few minutes instead of cold air, but ac overcomes heat after a short while. Are there separate blend doors that send air to different vent locations (windshield defrost duct, dash vents and lower heater output near floor) and one for heat on and off? Where are they physically located? Id like to use dash vents for ac and floor vent for heat, like i have in cars for decades. Fan motor seems to work fine. Thanks.

 

There are three separate doors inside the dash's HVAC plenum, each with their own actuator for inlet and outlet air selection as well as another for temperature control.

 

When looking at your HVAC controls on the dash, the dial to the far right determines where the air is being pushed to. You have various choices, dash, floor, defrost, or combinations of them. I would try each choice and verify that it is operating as chosen. If they do then there is nothing more you can do but if not then you at least know where to start checking.

 

Does the entire plenum have to be removed from behind dash for access to the blend door actuators, or can they be accessed from behind dash? Where would the one be located that controls the dash vents (vents you typically use for ac)? I know that one never closes.

 

FWIW, it sounds like you may have two separate issues, both in the climate control system.

This is somewhat ambiguous. Can't tell if you have a temperature blend door problem or if the A/C's refrigeration function isn't working right or if it's working correctly but not as you expected.

Assuming the basic manual controls and according to the factory service manual, yes. Requires A/C to be evacuated, heater core disconnected, and the whole thing comes out after removing the dash. I don't know if ambitious techs or DIYers have found a way around that. You' REALLY want to be certain of your diagnosis before going down that path.

You really need to first scan the HVAC module to see if it has any self-diagnosed fault codes stored. They can help focus attention where needed for diagnosis.