Temperature & fan speed not working

Help. 2008 SR5 with manual climate controls.

My fan and temperature controls stopped working when I reconnected the negative terminal of the battery. For several days it blew pretty fast and hot and I couldn't change the settings. When I removed and eventually replaced the 7.5a climate control fuse, it stopped blowing all together.

Waiting several minutes doesn't change this as it does for others.

I checked the two related fuses inside the cab; is there something else I should check? A relay perhaps?

I have a custom head unit which controls the fan and temperature. It worked fine for several weeks, but I had been fussing with it. I thought that might be the problem, so I swapped in my old known-good head unit and it behaves the same.

I ran Techstream to look for problems and found nothing.




What should I check next? Since the fan was working, but not responding to input, I feel like it's not the blower motor or mixing servo, but a component related to controlling the motor and mix.

I understand there's an AC ECU below the glove box. Could that be it even though Techstream doesn't show a problem? How could I test it further?

Thank you!!

 

Does the face of the climate control panel light up? Is it being powered? Green lights on?

The panel sends data signals via one wire serial to the AC amplifier (AC ECU) behind the glove box. It reads the signals from the control panel in and adjust servos ect accordingly.

If you go into Techstream home page, click on the Air Conditioning ECU, then click on live data you can see info from inside the AC Amp. You should be able to adjust things on the control panel and see a result in the Techstream live data on the screen of you laptop. This would prove if the AC ecu is properly getting signal data from the control panel.

If Techstream does not connect to the AC ECU, it probably is not being powered correctly.

 

That's great info, thanks. Because I'm an idiot I got rid of the climate controls when I replaced the head unit, so those troubleshooting tools aren't available to me at the moment. Off to eBay I guess.

 

It doesnt matter what you are using to send the control data to the AC ECU.

You can use Techstream to see inside the AC ECU to make sure it is properly receiving signals from your headunit. All of those headunits just clone the factory control panel output signals, generally speaking.

Hook up Techstream, going into the AC ECU and verify it is receiving and responding to inputs to change settings in the AC system. If the data is being sent from the AC control panel or the headunit shouldnt really matter. They are supposed to be sending the same signals.

 

Thanks for your help, Jeff. I double checked myself and the problem seems to be the head unit, so I'm taking it up with tech support.

 

Follow-up for future people troubleshooting this same issue. This was NOT caused by my head unit.

I think I fixed it by using a feature in Techstream that reset the AC controller. I stumbled across it and it indicates that you should use it after a battery disconnect or replacing the controller. The next time I hooked everything back up properly, the climate controls worked.

I can't be 100% sure if that fixed it, but the only other thing I did was remove and replace the relay under the hood.

 

I wonder if messing with or installing the headunit some how got some of the servos out of sync or something. I am pretty sure the Techstream thing just reinitializes the system. Regardless seems like your problem was jus a glitch or sorts. A full reset has it all working now.

At least now you have a better understanding of how the system works.