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Q: no heater control operation on 1998 Ford Ranger

my heater is all hot unless i turn it off.i replaced the heat control switch but it did no good so i replaced the other swich that controls the ac and vent direction but still does the same. i thought maybe a vacuum problem but i can see the heater valve turn off when i turn to a.c. max(only). also when i turn it off it will eventually turn off,
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i had same problem it is the vaccum under the air cleaner box. trust can't see it but it is there.
The temperature blend door is controlled by cable, as is the mode selector for the ventilation system.. Since you said the heater valve is working you need to see if the blend door cable is properly connected and operating properly. Normally the heater control valve causes the issue you have and on rare occasions the heater valve sticks internally despite the movement of the lever, so that should be checked. Good luck.
You say the system is all vacuum controlled, my reference showed cable controlled, regardless the one way I am thinking of tho eliminate the heater valve from the system is to pinch off the heater hose on the heater core side of the heater valve, then run the system and see if the air stays hot, if it does not, then we need to figure out if it is a vacuum control issue or the valve not working. If everything else is working as you said then then valve can be the only problem.
thank you for your advice. it sounds like that could be the prolem.i guess the way to check that problem is by looking behind the glove box. sincerely d.i.y.
after looking at the problem again,i don't think the blend door is the culpret.eveything is vacuum controlled. could there be a relay between the heater control and the vent direction control? i have 2 positions for fresh air only if the temp is at cold but if i use the heat at all it too stays on hot. only after a couple of days with temp on cold and all off will the frsh air work properly. is there a way to check the resitance of the heater switch from hot to cold? it seems to me like i have a sticky relay but i don't know where to look.
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