99 deville blower motor (wierd problem)

Hello, im a tech at a body shop here in town and i have a problem that has stumped me.
The car came in with the blower not working at all and the heater and ac programer not sending a comunication signal to the blower motor, but the control in the cluster was comunicating with the heater/ac programer. I have seen this before and determined the programer was bad. Replaced with a known good used unit (this is where it gets screwy) and the blower motor will now move, but only back and forth. It will not make a complete circle. so i removed the blower motor (not an easy task) and could not find anything wrong internally. So i come to the conclusion that the motor must be bad (allbeit a wrong one). So we receive the known good used blower motor, and what does it do, the same thing. So i check and double and tripple check the data line comunication, and everything seems to be functioning properly. Then i check the terminals on both the plugs (on the programer and the motor) and didnt find anything to be loose.

I dont think the digital controller in the cluster is bad because the data stream changes like normal when the blower speed setting is changed. also, i preformed the diagnostic self check and no codes came up.
:banghead: :banghead: :banghead: :banghead: :banghead:
Any help would be greatly appreciated.

thanks
anthony

Welcome to AF!
doesn't the '99 have instead of a standard resistor, an actual control module?
has this been checked? if the blower is benched, and spinning, and you have already swapped out the head unit, the control module is what I'd look at.
also, if your shop does not subscribe to AllData, or McLarens, call another shop local that you do business with, and see if their is any TSBs on the '99 DeVille. I know that the Auroras were having problems with A/C blower systems, might search their forums.

hope this helps,
chris
nrt racing

i must not have explained it good enough, the control module you speak of is the heater and ac programer, it mounts under the pass side of the dash. we replaced with a used unit due to no comunnication to the blower motor on the grey data wire. you are correct about it not having a resistor pack. the blower motor itself has the solid state circuit board that does the job of the blower resitor.
i checked tsb's in all data and nothing came up.

what my problem was the salvage yard said they bench tested it and it ran good. well when i got it i could get the motor to do nothing but twitch. my first problem was doubting my original diagnosis and takeing the salvage yards word on it being good. after another hour of double checking, i called them up to have them "bench test" this motor in front of me. they were being asses about it but they did and the guy could only get it to twitch. come to find out the guy who was to test it never did. so i orderd a new blower unit (the new units are a different design) and installed that today. it works great.

so lesson learned, never trust a salvage yard when they said "oh yea we tested it). lol

so problem solved and happy customer.

thanks
anthony