Ok I've checked, trouble-shooted, searched and I'm still baffled. My '86 with this damn C68 Climate Control started loosing blower speed control (going high speed when ever it wanted) a couple of years ago. So after reading multiple threads, I treated it to a new BCM (blower control module). Well the car was laid up most of last year, so the BCM got installed but not really tested. This year it's apparent the BCM didn't solve the problem. Now as soon as the car is turned on the fan speed goes HIGH, even if the Climate Control is OFF. Manual control of the fan does nothing but the fan speed numbers change. I believe all the other functions work.

I've also re-tinned the connector on the CC board, and everything on the circuit board looks fine. The blower "sensor" fuse is fine. I've got battery voltage on BCM connector C1, terminal B (red wire), and on C2 terminal D (the black w/red wire - although mine looks all black). C2 terminal A (black wire) shows good ground. C2 terminal D is showing 10.5v!? not 5.5 per the FSM (this wire is green w/yellow, not brown per my FSM-?)

I have no idea what terminals C1-A (green/yellow) and C2-B (gray) go to or test at. But I also checked the blower "sensor and got 10.5-7 there.

I'll admit I haven't checked to voltages at the CC head connector, as they are a bitch to get to. I'm just want to know if I got a problem with my Climate Control unit or did I get a bum Blower Fan Control Module. And I haven't had any luck finding BCM in the junk yard, hence the $100 bucks I dropped on a new one .

At this point I'm hoping one of you will say "yup, been there do this, or check that"

 

Well I'm still staring at my new Blower Control Module. I can't remember but I thought I purchased an AC Delco unit, it is stamped 12484912 and 52470337. It looks more robust than the old BCM, with a nice finned aluminum heat sink. 'Just wish I knew if it was a "good" unit.

 

Appears the color of some of the wires don't correspond to the Manual. Only wires you need to verify are the two small gauge wires on connector C2.

At the Blower Motor Module connector C2 the (4 wire) connector, the two heavier gauge wires are,

Black/Red wire is power from the Module to the Blower Motor.
Voltage will vary from 4 to 12 volts depending on the speed selected.

Black wire is ground.

The two smaller gauge wires are,

Brown wire is the signal from the HVAC control head and
determines the speed of the blower motor.

In the OFF position, there should be zero volts on this wire.

If you place your Red meter probe on the Brown wire and
the Black meter probe on the Black wire, turn the ignition
on and turn off the HVAC control head. There should be
Zero volts DC on the Brown wire.

If there is Zero volts the Blower Motor should not run. If it does
the Blower Motor Control Module is bad.
(You said you verified the 5 amp. feed back fuse is good).

Normal operation is when you manually turn on the Blower and increase or decrease the blower speed in manual mode,
the voltage on this wire should vary from around 2.5 volts with
speed set to 1 and around 7 volts when blower speed set to 10.

Dark Green/Yellow wire is used to turn on or off the Compressor
Clutch.
Zero volts on the wire = Compressor clutch off.
6 volts on the wire = Compressor clutch engaged.

The part number you listed is the correct Blower Control Module
for 86-89.

If the color of your wires on C2 don't match up to the color in the
Service Manual you should be able to figure out the correct
wires by checking the voltages on the wires.

 

Thanks Hooked. I'm gonna go check everything again, but you've pretty much confirmed what I thought; the Climate Control unit is bad. Not sure why my brown wire isn't brown, guess more GM goodness

Thanks

Continued: Looks like my gray(?) wire (B terminal) is the "brown" signal wire. I'm showing 7+v no matter what mode (including OFF). The green/yellow wire (C2 terminal D) looks to be, as you said, the Compressor clutch engage (10+v). Everything else works fine on this CC unit.