Author Topic: Blower fan operation 1975 Cadillac  (Read 2291 times)

R. Scot Minesinger

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Blower fan operation 1975 Cadillac
« on: June 06, 2010, 10:52:11 PM »

Looking for somone with some experience who can help me from re-inventing the wheel.  The fan on the climate control dies not work.  When I first got the car the fan only worked on high speed.  Then shortly thereafter the fan worked only on high intermitantly, and now not at all.

I replaced the "auto" fan relay.  I replaced the blower motor.  I checked the blower motor ground.  I replaced the "programmer", and there was a burnt electrical connection so I think that was good to do.  The only thing left is the dash controller unit.  Has anyone suffered the same problem and found the cure? 

There is a "low fan relay" but the spades are different than the "auto" relay.  The internal wiring looked the same as the "auto relay so I connected an "auto" relay in place of the "low relay".  Second question, other than used parts-does anyone know where I can get a "low" fan relay new?

Thanks for helping me,


Re: Blower fan operation 1975 Cadillac
« Reply #1 on: June 06, 2010, 10:58:37 PM »
This is just off the top of my head, but I have a '73.

There is a temperature sensor in the block that the blower is wired to that will
not allow the blower to come on in "heat" mode until the engine warms to
temperature.  If you have no blower at all in "heat" mode that's the first thing I
would check.  There is a procedure to track this down.

Refer to your Shop Manual for the details.

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R. Scot Minesinger

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Re: Blower fan operation 1975 Cadillac
« Reply #2 on: June 06, 2010, 11:06:01 PM »
Thank you.  I will check that out.  It happens in a/c mode too, but still it is worth checking out.  It happened on my 1970 and I fixed it.  Thanks for reminding me.

Offline Guidematic

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Re: Blower fan operation 1975 Cadillac
« Reply #3 on: June 07, 2010, 01:59:17 PM »

Placing the lever in Defrost will over ride the temp sensor, and if that is the issue, the fan will work.

 Off the top of my head, the contacts in the dash control also energise the fan circuit, but the programmer controls speed. The absolute best thing to do is access the GM shop manual for the proper procedure of diagnosis so you aren't just throwing parts at it. That gets pretty expensive in a hurry.

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Re: Blower fan operation 1975 Cadillac
« Reply #4 on: June 07, 2010, 05:11:37 PM »
I will suggest checking all the wiring connections in the blower motor power circuit.  The two power relays on the firewall and the connection that plugs into the programmer on the passanger side of the interior.  Be sure all wires are connected and the connections are not corroded or otherwise defective.
I would also check the fan motor itself by running 12 volts directly to the motor lead and being sure the motor ground strap is tigh.
Try that and see what you find.
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