Interesting problem I am having with my 97 4.6L. In the last few days I have noticed I am not getting much heat from my heater. It takes at least four times as long for for it to put out and still not so much heat as it always had. It has only been in the low 30's here. My first thought was thermostat. Well at least it was my hope. Off to the Ford place I go and armed with my trusty manual and a new one with o ring I install it today. Result still not putting out. Then I am on a test drive with it and I am now starting to think the worst when as I am playing with the hot/cold dial I started backing it off from full hot and WHAM! hello heat! About 1/4 inch back off of the **** from full it hits me at full heat just like it used too. I am assuming now that this **** controls some kind of proportioning system but don't know exactly what because I don't have my manual for the interior controls with me (volume 2). Any one want to venture a guess as to how this system works and what part is failing here? **** itself? A proportioning valve in the heater core system? But it seems to work fine at 1/4 inch back from full hot mark!

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97 F-150 SC Lariat, Styleside, White over Gold, 4.6L (Windsor), Automatic, 3.55 rear end, electronic 4X4, w/ every option of Lariat and ORP packages except the 17" wheels (I even got the OR decals now!), MOD's so far: K&N air box mod, Gibson Super Truck, clear Bugflector II, Leer TSC 600 hard cover, Bridgestone Dueler OWL ATP 265/75 R-16's, TrailMaster Invader N7 shocks, Smittybilt step bars, Ford moulded mud guards, "White-white" head lamps, Cloud Rider Design's SS Grill and bumper opening "Summer Grill's", Bosch platinum + 4's.

 

I don't have the manuals with me either, but, if I remember right, the **** electrically controls a blend door. It brings in air either through the heater core or the A/C evaporator (or a mixture of the two, of course). Maybe the control is getting a worn spot where you normally have it set to and you're getting a bad connection?

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Danny
'98 F-150 Std., RC, SB, 4x2, 4.2L, 5-sp, 3.08, AC, speed control, rear slider.
Mods: Mobil 1 engine oil, Red Line MTL trans fluid, Edelbrock IAS shocks,
50 Series Flowmaster, K&N with airbox mod, electric radiator fan, Superchip

 

Yes, thats where I was going with my theory too. Possibly it is a variable voltage to the mixer door motor and somewhere near the end of its (the ****) travel, rather than the voltage increasing proportionally, it is actually dropping off at the end and closing the door rather than opening it all the way. Does that sound logical? If so I need a new switch rather than a blend door motor?

 

I think we got it right. I'm looking at the manual and it shows that the **** is turning a pot. You may have a worn spot or it may just be dirty. I'd try some contact cleaner first.

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Danny
'98 F-150 Std., RC, SB, 4x2, 4.2L, 5-sp, 3.08, AC, speed control, rear slider.
Mods: Mobil 1 engine oil, Red Line MTL trans fluid, Edelbrock IAS shocks,
50 Series Flowmaster, K&N with airbox mod, electric radiator fan, Superchip

 

Yes, I was able to do some research last night in the manuals. There is a variable ohm thingy called the Blend Door Actuator Control. This is supposed to produce a 3000 ohm cold to 15 ohm hot in a linear fasion when you turn this ****. If I was to follow the test procedure with an ohm meter I would probably find the ohms are linear until the last few cm of turn and then they spike back up thereby changing the blend door position to an unfavorable one (colder). I think my problem is this actuator control rather than the blend door motor or the **** itself. Since it is working now I have to wait and see if it is going to re-occur otherwise my diagnostics would tell me nothing. Strange.