2002 Sonata Climate Control

The control commands high speed by grounding a relay. Other speeds are commanded by duty cycling a power transistor. There are several possibilities, but I'll give you ten to one odds the problem is the power transistor.

And that looks to be located somewhere near the blower according to the schematic. Thanks for the tip!

I can't recall whether it's behind the center of the dash or in the blower box where the resistor would normally be. The schematics have links at the bottom of the page. One of these is for a component location index. Follow a couple links, and voila, you've got a nice picture of whatever dealie you're looking for.

Unfortunitly the PT isn't the issue or at least not all of it. Installing a new one didn't resolve the problem. Do you have any other ideas?

It's possible the issue is in the wiring or the climate control itself. Neither of these is a high frequency failure and the climate control head is rather expensive. I'd therefore recommend spending the time to check the wiring thoroughly.

Unplug the power transistor. Check to see if you have voltage present in the Black/Orange wire. It may be somewhat reduced from 12V (depending on your testing device) because it goes through the blower windings prior to arriving at the power transistor.

Check for ground in the black wire. You already know the connection at the ground location is good because the fan works on high speed and this uses the same ground lug. Your voltage between the black/orange wire and this wire should be very close to the same thing you got in the above test.

Check for continuity in the Green/Black wire. You'll need to remove and unplug the control head and check from one end to the other. Also check to make sure this wire isn't shorted to ground (i.e. check the resistance between the wire and a verified ground and verify it's an open circuit).

If these three wiring tests check out and the power transistor is known to be good, then you have a defective control head.