heater controls not working

[grante]

I have a 2001 ford explorer sport trac 4x4 with the 4.0 liter 6 cyl. automatic. The only contol that works correctly is the fan switch. The heat contol does not have any control over the heat received in the interior and the heat position controller does not change where the heat comes into the interior. It only blows throught the defrost vents regardless. Every once in a while for no reason it does start blowing warm air on its own and then goes back to blowing ambient air (outside temperature) . I replaced the vent location (air control) switch without any change. The few times I have managed to have the heat come on you can see that the heat vent position controls (behind the glove box and up under the drivers side) have moved position but when blowing only ambient air they do not move regardless of vent control switch position. I have not found any troubleshooting guides anywhere ( including internet and YouTube) that even hint at this problem. I am hoping someone out there has seen this before and can point me in a better direction. I have been a mechanic for 51 years and made the transition from points and carbs to electronic controls with no problem. At least until now. I only work on autos as a hobby now so this is a big frustration to me. Please help if possible.
Thank you for your time.