heater control problems

[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.

 

[crunchie_frog]

have you checked your vacuum lines that control your heater bypass valve and control your ducts?

 

[grante]

Yes, as far as possible, unfortunately I have not found a good vacuum diagram for this system in any of the manuals I have looked at. If you know of a good diagram please let me know. Along with that I have not found a good electrical diagram either. At this point I am unsure if I am having one problem(vacuum) or two(electrical).
Thank you for taking the time to respond.

 

[crunchie_frog]

on my 5.0, the vacuum line comes out of the front of the manifold and tees off. One side of the tee goes towards the passenger side and connects to a vacuum reservoir (a ball like a toilet float ball). The ball is up above the very front of the wheel well. If you cant find it, trace back the line from the heater control valve (it is connected to the vacuum motor on the water line going to the heater core). It should be a gray line, this line connects to the same line that comes out of the vacuum reservoir. if you have recently done work anywhere in the engine compartment or under the wheel well, you need to check all of these lines closely and be sure they are not broken. Taking off the inside wheel well cover allows you to see all of them. At least this is the case for my 5.0. The line then goes inside the through the firewall and you can start to trace it on the inside there. You can remove the glove compartment and likely see the lines. they will be different colors. like white, blue and red I think. Any leak anywhere and your system faults to defrost (like you are saying yours does).

you can try google images to give some diagrams to get the general idea. I do not have one.

good luck

 

[albi1cnobi1]

Crunchie_frog is correct. You likely have a vacuum leak. The setup he described is the same on the v6. The vacuum reservoir is above the inner fender on the pass side. Vacuum comes off of the intake and goes to the "toilet ball" (very nice, I like that) and from there goes to the heater bypass valve. It's below the alternator. It also tee's off and goes thru the firewall to feed all the internal controls. Like frog said all of the internal lines are color coded. The most likely culprit is either a cracked vacuum res(sometimes they get water in them and then freeze and crack) or a cracked line.(the one in the engine bay are hard plastic.) Start your search there.

 

[Turdle]

This thread might help

http://www.explorerforum.com/forums/showthread.php?t=192842