Blower not working on high fan speed

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Aggiesrok

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2012 Expedition Limited with dual automatic climate/heated/cooled seats.
Replaced the blower resistor, old one had a small melted area near a contact and on the pigtail. Replaced pigtail also. The AC works great on all settings except HIGH. When you place it on HIGH is works for about 10 seconds, then stops, after a minute or two it comes back on for about 10 seconds and stops again. The cooled seats work fine also. I ran the EATC diagnostics and received no errors.
The resistor obviously works and the blower motor obviously works. So why doesn't the bypass work for HIGH?
 
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Aggiesrok

Aggiesrok

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Thanks for the link, but I have an automatic climate system and so there is probably a computer control in the mix somewhere.
Also an update, it still doesn't blow on HIGH, but now it only blows hot air, front and back. So it gets worse.
 

stamp11127

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Since you have the electronic razzle dazzle temp control your system doesn't use the old style resistor pack. It is now controlled with microprocessors - aka the little black box.

I would expect you are seeing excessive current draw on the high setting which is tripping a FET (transistor set up as a virtual fuse) or the black box is cutting out the blower relay. As a test you can run on high, once it fails immediately switch to a lower speed. If it works on the lower speed it isn't the relay.
 
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Aggiesrok

Aggiesrok

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Since you have the electronic razzle dazzle temp control your system doesn't use the old style resistor pack. It is now controlled with microprocessors - aka the little black box.

I would expect you are seeing excessive current draw on the high setting which is tripping a FET (transistor set up as a virtual fuse) or the black box is cutting out the blower relay. As a test you can run on high, once it fails immediately switch to a lower speed. If it works on the lower speed it isn't the relay.

Thanks, there seems to be a different resistor for the electronic temp using actual numbers to set temperature as opposed to the cooler/warmer button. I didn't know it was available until yesterday, so I ordered it and will try tomorrow.
So another question - can the resistor tripping a FET cause the whole system to stop allowing cold air to flow?
 

stamp11127

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Yes but a different module is responsible for that. Doesn't hurt to check fuses with a meter or test light. See fuse testing 101 in the electrical section.
 
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Aggiesrok

Aggiesrok

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I pulled and checked all the blower related fuses as well as the High Power relay. They were all functional.
 

stamp11127

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Doubt there are any additional codes that would show up on a generic scan since the EATC can run diagnostics and return codes.
When you checked the fuses did you also check to see if they were getting power?
 
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