that was a link posted on a vw forum. looking at A12 pinpoint test in the ford troubleshooting pdf, the range is 50 to 300,000 ohms. I don't know what the resistance at ambient temp is supposed to be.

DOE

 

OK so I have this one on order and it's supposed to be here Thursday so I will let you all know how I make out when I install it.
Invalid Request

I have researched many of different auto forums and even a thread about a heated seat on a motorcycle. They are all pointing to the thermistor but it is very confusing on which one to buy because here is some of the info from other sites

"In a thread about repairing non working heated seats someone who had used aftermarket heating elements but kept the factory switches / wiring.

They indicated a 6,8k ohm button style thermistor is basically the same thing as the temp sensor and could be purchased locally from an electronics store or radio shack.

The switches in the dash must see a value from the thermistor or no voltage will be sent to the elements.

A resistor of 8k ohms can be wired in place of the temperature sensor but the end result is a ON / OFF situation with no adjustment with the dial."

"Next measure resistance between the blue wires going to the thermistor -> should be less than 10kOhms if the heater element surface temperate is around 20°C
-> If infinite, either the thermistor is broken or the blue wires have a snap somewhere
- Desolder the blue wires from brown and black/white wires
- Remove the heater element a bit further, the thermistor is right under your bunghole when sitting
- Carefully pry the element underside open around the thermistor and remove the thermistor with its wiring
- Now measure the thermistor resistance from the solder points on the thermistor, should be less than 10kOhms if surrounding air temperate is around 20°C
-> If infinite, go get yourself a new button-style NTC-thermistor from your local electronics shop, value should be around 6,8kOhms for correct operation"


Some of the other car forums are pointing to the one that Double Ott suggested and the one I purchased. So we will see if it works when I get it all put back together.

 

Okay, I'm going to hold off Subjim until you get that installed and see how it goes. Thanks DOE, I missed A12, exactly what I was looking for. Both my thermistors measure open resistance, so I'm sure both are broken. So probably my good pad will eventually burn out also if I leave it on too long. I guess that is the thing that still confuses me. If the thermistor is broken and the circuit is open then what is the difference in that and not having anything in there at all? Why would the system still heat the pad with an open thermistor but not work at all with just an open circuit there? When I installed the bi-metal switch I could see the module not initiating current flow to the heating element because it was not sensing between 50 and 300,000 ohms, but why would it initiate current with an open circuit?

There is a data sheet on the thermistor DOE put a link to which is supposed to tell the resistance at certain temperatures, but I'm not smart enough to read it. And we still aren't positive whether Ford uses a NTC or PTC thermistor.

I really think we have this thing nearly nailed down. All because you can't buy the stupid replacement pad for this vehicle seat anymore. After all the hours I put in to tracing this down I would have gladly spent $50 bucks for a new pad. I really didn't want to spend hours rewiring a replacement system, I wanted to use what was there and if we can figure out the thermistor part we will be able to repair any heated seat pad that uses a similar system.

Thanks for all the help guys, this place is the best! Let us know how that goes Subjim, I will be anxious to hear from you.

 

rad1026:

Will do...to be continued

 

Okay, I apologize, I'm an idiot. I kept saying my thermistor was not functioning because I saw an open circuit when I measured resistance across the leads. Well, I learned something about my meter this morning. When the ohms rise above the scale on the meter the display show the number 1. I took that to mean the circuit was open. I was looking for a much lower resistance measurement, but after DOE showed me the A12 pin test that says the resistance should be between 50ohms and 300,000 ohms I retested the thermistor I removed from my pad this morning. At about 54 degrees in my garage I measured around 12k ohms. I took my heat gun out and warmed up the thermistor and it went up to over 100k ohms. I got a bag of frozen veggies out of the freezer and the ohms started to drop fast. I didn't have time to do much more but it seems to be working correctly. Tonight I will see if I can get the temp to 25C and take and ohm measurement. Then I think I could use the data sheet on the thermistor from digikey and see if that is the correct device to install.

 

FYI - for those that find this thread through a search that need to replace the heating pad in their seats the closest heating element I've found is DORMAN 641-205 - the plug is identical although the pad is a little shorter. I'm going to install mine here before too long.

 

Thanks for this thread. Fixed my drivers seat yesterday, wire in element burnt. Got to find out whats going on with pass. seat couldn't see any burnt wires.

 

What did you end up doing to repair it? Did you replace the element? If so with what?

 

Rad1026: Definitely let me know what ohm reading you're getting at 77°

 

Well got the part today and I am in the process of installing it in the pad. I will install the pad in the truck tomorrow and see what happens. I knew the new Thermistor was small but WOW!

 

I just cut about a half inch if the element out and soldered the wires back together.

 

So...after trial and error and a few suggestions from the good folks on this and other forums I did it. But not without it fighting me to the very last moment. I went out today and installed the repaired heating element in the lower part of my seat, put it all back together, hit the button and waited...and waited...and waited. NOTHING!! What the F**K? Well some head scratching and a few choice words later I remembered that the back section and the seat section heating element are wired in line with each other so I figured I would check the element in the back section of the seat. It was never part of the problem so I just assumed it was OK. After checking the continuity of the pad it wasn't OK. So I disassembled the back and sure enough one of the wires from the pig tail had pulled off the little thin wires that run throughout the pad. After soldering I plugged it all back in and hit the button. It WORKED and worked well. So I just want to thank everyone for their knowledge and advice. If I can help anyone down the road let me know.

 

congratulations! this is the first I have heard of any problems in the seat backs. thanks for the posting.

DOE

 

rad1026:

How did you make out?

 

I haven't heard this one yet
My drivers side heater won't shut off. Started two days ago I have to keep my seat cooler on and even then it's very warm