I just replaced the ECM in my 89 this morning to correct an over rich condition. I ran the car around for a couple of hours and it seemed to be fine. Now this afternoon the AC/Heater blower motor runs wide full open whenever the key is on. Even with the heat/ac button is turned off. The temperature control and the vents seem to be working normally and the controller fan speed number changes when the button is pushed. But the fan blows at maximum speed even when the fan speed display reads one.
My question is does the HVAC circuit go through the ECM or is this just a very bad coincidence?
I understand that there is a fan relay that could also be the culprit. Could anyone tell me where this relay is located?
Also does anyone know a reputable source to get a replacement ECM? I went through 3 of them from the GM dealer before I got one that would even start the car. And I am very suspect of the one I have in there now.
The car is my daily driver and has been very reliable for the couple of years I have owned her. The ECM acted up and now I think she’s possessed. It’s very frustrating but she is way too good of a car to ever give up on.
Thank you for your time.

Glen.

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Your car has a blower control module which is bad, usually in the evaporator case. Blower is controlled by a circuit board and a transistor which is shorted out. Changing the ECM won't have anything to do with it. Did you replace the prom or pull yours out of your old ECM? I am surprised that the dealer had an ECM. 86 - 89 Vette computers had a lot of problems. 86 was the first year of a higher speed data rate and even GM had trouble rebuilding their own ECM's. They finally turned it all over to A/C Delco. I bought an A/C Delco remanned for my 86 with no problems. If you have a parts house that can get Delco, that's where I would go. Also, check with GM to see if there is an updated PROM for you car. A lot of the scan tools even now have trouble reading data from my 86. [8D]

 

Hello,my friend.If I may put my two cents in,it may be possible for you to have a short somewhere.You just never know.I hope you find your problem and eliminate it,just because of what you said and how we ALL fell about our cars;you just can't give up on them no matter what.Good luck!!! Your friend,Joe.

 

Thanks for the replies.
I did reuse the old prom. According to my dealer it was the latest available.
I take it that you have to pull out the evaporator case to get to the suspect blower control module.
Does anyone out there have any experience doing this? I did the heater core a few months back and that was not so bad. Any short cuts or tricks to get at the BCM would be appreciated.

Thanks.

Glen.

 

The case is under the hood on passenger side and the module should be handy there.[8D]

 

Thanks for getting back to me.
I pulled it out.
Is there anyway to check this unit out?
Also is this a dealer only item?

Thanks.