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Just for Search in this section, based on recent thread in Parts For Sale / Wanted I'm bringing over diagnostics uncovered myself and intel gathered from others on this problem.

Since this a combo age and temperature type failure it seems will become more and more evident in our rigs. The story starts when noticing after 5 minutes on the interstate that the A/C switched from 'normal 65 high' sounding blower up to the '60 supermax' speed - all on its own. It had never done that before (nor in my last FWB for 16 years) but did not see a big deal at the time. When parking and jumping out I just happened to halfway notice that the blower remained on after turning off the engine.

Recalling the strangeness earlier on the highway I figured it had to be a welded closed relay (with Climate Control it's called a module) so to keep from a dead battery after an hour I tried pulling all the IP HVAC related fuses but it kept running strong. I wasn't going to start yanking fuses under the hood so ran back home and got out the Impala SS and resumed plans. I got to hunting for a used 16173860 Blower Control Module based on FSM:

Tearing the old part apart I noticed the (scant and dried up) thermal paste and glad it lasted over 20 years in the first place:

I snagged one used from a Vette ($38) off ebay and *$%# - rats didn't work. I ran the diagnostic (20 more times), checked a bunch of grounds and even did extra testing from here:

So, I admitted defeat and ordered a new one, but opted for the "not $110 ACDelco branded unit but instead the $35 Jeep Cherokee unit" option.

Plugged in and VOILA! But there's a catch. Or two. 1.) The bracket and bolt mount is different. No big deal, just 2 screws and switch them:

2.) The heatsink is different. Even with the original mount I had difficulty lining up the screws and tightening. The fins on the Jeep heatsink are interference with the side of the plenum. With thermal paste left over from a computer repair I could have easily switched heatsinks:

But, I decided smarter to leave stuff alone and simply double up part of the foam seal from the old housing to tilt the whole unit a few degrees away from interference and still retain a decent seal (think "doubling the back part of the exhaust manifold gasket to seal a No. 7 or 8 broke off bolt...")

That's about it. Any time I'm near the blower motor on these cars I just drop it to remove junk that is guaranteed to be in the cage and add 2 drops of 3-in-1 to the motor. Blower speed ALWAYS improves:

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