1979 Heater blower control module

[Dan Marinola]

Does anyone know if there is a procedure to check the SCR on this module? The fan keeps running after you turn the key off. Any help greatly appreciated. Thanks, Dan

[Guidematic]

Sorry, but what model of Cadillac are we talking here? And does it have Electronic Climate Control, or the older system tthat uses the dial?

But typically if the blower motor keeps running on a car equipped with ECC, then it's the power module located in the heater box.

Mike

[Dan Marinola]

Hi Mike, this is the module that goes in the heater box under the hood. It sets right near the blower motor,on the right side and is held in by two 5/16 screws. It has  an electrical connector on it with about five wires on it. This style is the one with the temp dial and lever that sets in the lower center of the dash. I guess that would be considered the older style , as compared to the one with the buttons that raise or lower the temp setting.

[bill henry]

The thing in the heater box is the blower resistor . I would look at the rotary switch connected to the lever in the dash control unit. the same thing happened to my 78. I might still have an extra resistor but I dont believe thats your problem.bill henry

["Cadillac Kid" Greg Surfas 15364]

Dan,
It kind of sounds like you have a blower relay that has welded it's points together.  If the device you are talking about has one three wire connector and a single wire connector then I would suggest trying a new relay.
Greg

[bill henry]

the blower relay in 79 is under the dash next to the fuse block and is a plug in. bill henry

[DaveShreiner CLC#23834]

Forget the blower motor relay under the dash.  I have wasted about 5 of them.  They all meltdown internally from too much heat in the electromagnet inside.  My solution was to disconnect the relay and chuck it.  First, note where the blue and brown wires are.  These you will cover with tape and forget about.  The two other wires should be connected by solder, but not until you connect one to a spot on the fuse box that is only ON when the ignition key is turned on.  If you don't do this, the blower will run all the time as it does now for you.  Then your A/C and heater will work the way it is supposed to. 

Don't forget to disconnect your car's battery before doing electrical work!

[Misfit]

So basically what you're saying is to remove any safety feature built into the system??   

Then the wires get hot, start a fire and the man is out a car. 

Uh-uh, not me. That relay is there for a reason. If you keep melting relays, you have a serious problem with resistance somewhere.

Fins

[bill henry]

there was a Bosch relay that was sold as a replacement for the plug in back in the day that was much more robust and did not heat up but needed to be wired in. I put one in my 78 along with a new rotary switch.  bill henry

[DaveShreiner CLC#23834]

Wires get hot when too much current flows through them.  The blower motor in 79s draws too much current and eventually melts the plastic parts inside the relay.  Large gauge wires reduce the heat and should be used in the blower circuit.  The blower relays are notorious for failure on these cars, and the replacements are no better or worse.  Perhaps the Bosch suggested by someone would work better.  No relay works for me just fine.  Fire is very unlikely.  If a wire gets too hot, meltdown of plastic insulation and grounding will blow a fuse -- that is the safety feature.