Automatic Climate Control Not Working

2006 Mazda5 with automatic climate control

I had a loose LED in the climate control unit. I removed the climate control unit, re-seated the LED, verified that the LED was working correctly (the control unit and all the buttons were also working fine at that time), and started to reinstall the control unit. In the process of doing so the temperature reading that appears on the LCD suddenly disappeared. Since then the climate control unit has been effectively paralyzed. None of the buttons or dials work. The dials are illuminated though, they just do not work, and neither do the buttons. The ambient/internal temperature reading is gone. When I start the car there is warm air coming out of the vents, which is good, because it is winter here in Canada. However, I suspect this might be some kind of a default setting, not sure what is going to happen in the summer ;-)

What I tried:

1) Wiggled the control unit wiring harness, try to push/pull each wire. No difference.
2) Cleaned the wiring harness using an electric contact cleaner. No difference.
3) Checked all fuses (but not relays) in both the engine and passenger areas. All fuses good.
4) Pulled out and re-seated all relays in the engine compartment areas.
5) Disassembled the control unit to check any signs of charred areas. No obvious problems found.
6) Ordered a different control unit from eBay. Long shot, but the price is better than having the dealer do the diagnostics.

In case that the other control unit does not make a difference, any ideas on what else I should be checking? I.e. any additional thoughts on what may be broken here?

Thanks a lot.

It was the control unit. Spent the entire weekend studying the wiring diagram and checking the voltage at each connector pin. No shorts, most of the pins were OK except for the 5 V ones which should have been supplied by the climate control unit. The manual was also suggesting this was due to a faulty control unit. I decided to get a quick replacement from a scrapyard. Worked immediately, all fixed now. The remaining question is WTH happened to the old one. I was being careful while installing it, no twisting, pulling the cables, or anything of that nature... Oh well, I guess when the s...tuff hits the fan...

Glad you were able to fix it! (2thumbs) Electrical gremlins can be a bear. I would've guess a stuck servo affected by the Canadian cold where you are... Well done!