Hunner did a write up. I don't remember if there were pictures. But here is the text I saved.
This should fix the problem of turning the far left climate control knob off of max cold temp and have it blow hot air with no variable.
I did some searching and someone else discovered this fix, not sure who originated it.
This supposedly would get the reference voltage (5 volts?) regulated again if the switch circuitry has failed or wherever the 5 volts originates.
The light blue with black stripe wire, terminal f circuit 1688, on the driver side of the hvac control head needs 68 ohm 1/2 watt resistor installed inline.
The procedure here is the HUNNER method of installing it. Proceed at your own risk.
I did not disconnect the battery as I wanted to confirm this resistor fixed it instead of by some fluke disconnecting the battery did.
Set the parking brake. Turn the key on.
It helps to shift to Low. However leaving the key on will drive you nuts so after removing the dash piece I put it back in park.
Disconnecting the battery would of course shut the dinger bell off. So I would recommend that and you can leave it in low to have more room, now that we know this did fix it. (fingers crossed)
First you have to do the stick your fingers in the DC sockets and pull up and out.
I cut me a piece of cardboard for a work surface in case solder dropped.
I disconnected the plug from the back of the switch to get more room to work
Find the light blue wire with black stripe. I peeled back the high quality gooey sticky black electrical tape GM chose to use far enough to expose the wire back into the loom so I could slide on some shrink wrap long enough to cover the splice.
Call me old school, I'm old and went to school, but just as in my battery thread I make a physical connection first then solder.
I used some forceps for a heat sink.
I used a Radio Shack 68 ohm 1/2 watt resistor. They come 5 to a pack for $1.30 or $.26 a piece.
If you don't know, use a low wattage iron so as not to fry the insulation on each end. Heat the wire until it pulls some solder as you feed it.
Use some fine solder, Radio Shack still has that!
Grabbed a short piece of shrink wrap I keep around. After the solder area cools slide the shrink wrap you remembered to slide on BEFORE you soldered over the entire splice. Use a heat gun carefully to shrink the wrap and secure and insulate your splice. I did not re-tape it at this time as I wanted to test it first. I will use a high grade of black electrical tape or some loom.
Now in transitional fall weather you can adjust the air temp but leave on the air conditioning to freshen your cabin temp and humidity!
