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Weird HVAC temp adjust issue

S

SilvFroCSVT

CEG'er
Joined
Dec 4, 2009
Messages
113
Location
Tampa, FL
So recently my temp control decided to stop working properly in my 98 Contour SVT. If I turn the temp knob to any part of the blue section it will be max cold and if I move it just into the red section it will go instantly to max hot. There is no in between anymore for some reason and it's really frustrating because I'm either freezing or too hot! I've even swapped in a whole new HVAC control panel from a junk Contour and same thing. Anyone ever heard of this one one? Thanks in advance!
 
The blend door actuator is probably failing. I believe it is an easy fix on the contour.

Impossible to get to on a Taurus.
 
I actually swapped a different blend door actuator as well and no difference. I watched the blend door shaft while I rotated the temp knob and it either opens all the way or closes all the way when I rotate temp knob slowly from cool to hot. It's not partially opening like it should when not on max cold or max hot. It's like there's a variable resistor or something that has failed in the circuit. I thought the temp knob was the variable resistor that would control how much the blend door opens or closes correct?


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You would think - must be something else in that circuit. I could look in my wiring diagrams later tonight.
 
It is possible the switch on the control is bad. It is a resistor type of control that adjusts the power to the actuator.
 
I actually think it has to be that switch too... I tested the resistance with a multimeter across the white/black and brown/yellow wires on the back of the temperature knob 3-pin connector and I think it's supposed to go from 800-5000 ohms when turning the knob from cold to hot according to a link I found online. The resistance I got was nothing close to that. Not sure how I could have got another bad temp switch from the junkyard, but I guess it's possible. Can anyone verify the correct resistance I should be seeing from the switch? Thanks!!
 
SilvFroCSVT said:
I actually think it has to be that switch too... I tested the resistance with a multimeter across the white/black and brown/yellow wires on the back of the temperature knob 3-pin connector and I think it's supposed to go from 800-5000 ohms when turning the knob from cold to hot according to a link I found online. The resistance I got was nothing close to that. Not sure how I could have got another bad temp switch from the junkyard, but I guess it's possible. Can anyone verify the correct resistance I should be seeing from the switch? Thanks!!
Click to expand...



If I'm correct, the variable resistance should be smooth. Don't know the values, but turning the knob should result in a smooth rise and fall of the value depending on the direction you turn it.
 
SilvFroCSVT said:
Heading back to the pick n pull today to try and grab some more temp switches. All wiring checked out and it brings me back to the potentiometer switch. I have no continuity between pin 4 and 6 on the BDA connector. This link I found was a huge help for anyone interested!

http://www.factoryairtemp.com/Uploa... Tips/FA4S 356 FORD'S BLEND DOOR ACTUATOR.PDF
Click to expand...

The resister pot in the switch is bad. It is likely broken in the middle where it usually breaks. It will operate at full not or cold because the contacts are made, but in the middle, it is not making contact because the pot is not good.

One time on one car I did get it to work by cleaning the pot with an electrical cleaner spray. WD40 works as well.
 
UPDATE: Snagged a few temp control switches today out of various contours/cougars from the local pick-n-pull to have as backups. Swapped one in and sure enough problem is fixed yayy!! I actually took the original switch apart last night to inspect it and noticed the black dielectric paint or whatever was chipped off a little and the rest came right off with my fingernail... Just a worn out potentiometer. Can't believe I got a bad switch twice in a row. For anyone else who has this issue, just grab some temp switches out of newer cougars if you can find them and don't even mess with the old defective one. The good ones I have found say BOURNS on the back of the switch right below the 3-prong terminal.


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