99 Cadillac STS – A/C blower fan repair

Right on cue for the super hot summers here OK, the A/C has gone out.

History

Been working fine, nice and cold no issues at all.

Last week, driving home from work, A/C on max ( it was 105F out), blower on about ~70%, just as I got home the A/C stops, well put it this way, the blower just quits, the A/C compressor is still working.

I stop and start car, no difference, I then left the car for around an hour, tried it again, everything starts working again.

I drive the car, with A/C on, just as usual, and it works fine, until this Saturday, when the blower just stops – however this time it will not come back on.

I got the impression that the blower was only failing when it was set at max, thus drawing the most current, when I lowered the blower speed for a week the blower worked fine…for awhile…then a week later, when I turned at to max again, it worked for a hour or so, then went out permanently, the blower for the rear passengers still worked, but wasn’t putting out much.

Blower location

The first  problem was locating the blower,  for a 99 Seville STS it is located under the dash, passenger footwell, you have to remove the “hush panel” to get at it, also remove the glovebox, you have to pop-out the glovebox light assembly before removing the glove, can be tricky, but you have to do this.

Caddy A/C blower assembly, front passenger gloveblox, in the footwell

Caddy A/C blower assembly, front passenger gloveblox, in the footwell.

  • Blower Assembly ( circled in red, 3 wire power connector to the fan)
  • Blower Control Module (BCM, circled in blue)
  • Instrument Panel Integration Module (IPM) – also known as HVAC control module, where you set the temp/blower speed and has the knobs/dials etc

Note: The partially obscured module in the lower right corner of the photo is the DIM (Driver Information Module), it plays no part in this.

To cut a long story short, well  a little bit shorter, I replaced all 3 of the above mentioned parts, the blower purchased new from RockAuto (~$80), and the other 2 from ebay (~$35 & $50) and the fault still persisted, I figured I could either return the parts or re-list them on ebay, in the end I returned all the parts, took a hit, 10%, 15% and 20%, plus shipping, still, it proved an easy way of eliminating suspect components from issue, and still a hell of a lot less than if I’d taken it to a Caddy dealer, they would have charged a couple of hundred just to look at it I’d imagine.

The Fix

After much head scratching, testing and measuring of voltages and the such like, the fault was that too much current had been pulled by the blower and had melted the ground terminal box which is located under the carpet, in the front passenger footwell, this cigarette packet size black plastic box is screwed directly into the body work of the car and is used for terminating several grounds, there was a very small bubble of melted plastic where one of the wires enters, and had obviously melted and insulated the ground wire for the blower, rather than take the box apart, I went to Home Depot and got a brass screw terminal fitting, snipped the ground wire and added this fitting to the terminal box, the blower started working and has been fine ever since. Probably best to solder the connection for a more long term fix.

Ground mod (brass fitting) to the terminal box located in passenger footwell, under the carpet, note the melted bubble of plastic, the source of all the trouble

The following circuit diagram came in very very handy for diagnosing the problem.

A/C blower circuit diagram

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About hedscratchers

A UK ex-pat now living in the USA.
This entry was posted in Cadillac Seville STS (Pre-2003). Bookmark the permalink.

One Response to 99 Cadillac STS – A/C blower fan repair

  1. ryan dishner says:

    which ground wire on the ground dist. cell is the blower ground? they labeled w/ letters

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