1970s 1974 Eldorado Blower Motor Will Never Stop Running When Ignition is Turned Off

[motard]

I have a 1974 Eldorado and the blower motor will not stop running when the ignition is turned off. It runs until the battery is dead. I have changed the engine block sensor by the alternator that controls the grounding of the blower motor. I have also changed the blower motor relay underneath the hood on the firewall. The blower still does not turn off. Once it runs the battery totally dead. The blower motor turns off and stays off even after you recharge the battery. Once you start the car and the sensor engages the blower motor turns on, it will not turn itself off when you turn the ignition off. It only turns off when it runs the battery down.

What help can anyone recommend? Is there another sensor or relay inside of the car underneath the dash?

[Dave Shepherd]

If you look at the wiring diagram, the blower is initially  powered by the ATC key off these components should not be powered, start looking at how this is happening at the source.

[TJ Hopland]

Others will have to confirm but I think 74 the blower runs on low any time the key is on even if the climate control is selected to off. 

How long have you had this car or is it new?  Anything else not working or staying on? 

Is there anything not stock or recently changed on the car that you know of?  Like an ignition/distrubutor or alternator work?  I don't think there is a really likely suspect in the climate control system but more likely something else is going on that is backfeeding at least part of the key on circuit so as far as the climate control knows the key is on and its just doing its thing.

[Dave Shepherd]

Correct, the blower is on low, system off, key on.

[motard]

I have had the 74 Eldorado since 1995. The horn does not work and the right seat will not move back and forward. I changed the relay on the seat a very long time ago. Before the problem with the blower motor. The seat still will not move back and forward. It appears to be a problem with the seat transmission. Everything else works like it should. 

[TJ Hopland]

When its doing it what happens if you move the mode lever to auto high or DEF?  I'm wondering if the blower speed goes to high?   I'm also assuming when its stuck on its on low?

So if you were to disconnect the battery while its stuck then re connect it will stay off?  What makes it stick on again?  If you just turn the key on will that stick it?  Key on and and High or Defrost?

[bcroe]

The blower should not run with ign off.  Tracing back
through the wiring the power running it, should find
the source that is incorrectly keeping it on.  I am a
fan of first identifying the exact problem before fixing
it, not just throwing parts at it.  Bruce Roe

[TJ Hopland]

How does everything feel in your steering column?  Is the tilt still nice and solid? Do you tilt it very often or at all?  Does it seem like there is any slop when you turn the key?  I'm wondering if maybe something is causing the ignition switch to not be in its expected positions?   I used to see a lot of issues in the trucks where people tended to use the steering wheel to pull themselves up into the seat.   I had one truck where you could actually get it to start by wiggling the column/wheel.   I didn't see this in cars but its worth considering and should be fairly easy to test.

For those that have not had to mess with this part of a car its actually a fairly complex system.  It starts with a rack and pinion setup at the key.  The end of that rack had a slot in it that a rod engages.  On the tilt columns this is a curved slot.  The ignition switch is mounted to the side of the column under the dash and operated by the rod. 

The switch itself is also more complicated than you would think.  Its not like a much earlier car or a garden tractor with just a on and crank terminal.  These have several contacts and terminals that disconnect some things during cranking while leaving other things connected so you can get odd things where some things work and some don't.

[motard]

The steering column feels fine. I never tilt the wheel.
Key off after the car has been running and the engine is at operating temperature;
1. Off - Fan runs very low speed and blows out the floor vents.
  Low - Fan runs at low speed and blows out the dash vents.
  Auto - Fan runs at high speed and blows out the dash vents.
  High - Fan runs at high speed and blows out the dash vents.
  Defrost - Fan runs at high speed and blows out the windshield vents and floor
            vents.
Please keep in mind that all the above is with the car turned totally off and the key removed. The fan will only turn off when it runs the battery down or you pull the hot wire off of the fan itself underneath the hood.

[motard]

When I disconnect the battery and reconnect it, the fan immediately starts back to blowing.

[TJ Hopland]

I will have to think about this a bit and see if I have 74 manuals, I don't think I do so I may have to compare 73 and 75 and see if I see any likely spots that circuit could be getting backfed from.

Anyone else have ideas?   Since the climate control seems to be operating correctly I'm not thinking that is where the issue is. 

Does the AC still work?

[cadillactim]

Did you check both blower relays? There is a low relay and an auto relay, they are beside each other.

One relay may be stuck. If I remember correctly the blower relays gets main power from the battery. The relay is energized from the ignition switch. If the relay contacts are stuck closed the blower will run if either of the two thermal switches allow the ground circuit for the blower to complete.

Tim

[TJ Hopland]

That was the sort of things I wanted to find out from a diagram.  I was thinking that the blower power didn't actually flow through the key/ignition circuit. 

Are the 2 relays the same or same as anything else in the car?  Are they like the blower relay used in the 77-79 where they seem to be a little more complicated than they need to be?


One of the reasons blower relays (and or control modules) are often a problem as our cars get older is because something changes that puts a higher electrical load on the circuit.  This change could be something minor like years of debris or a small refrigerant/oil leak internal to the system slowing down the air flow or a bearing in the blower motor not as well lubricated as it was when it was new. 

Especially in the last 20 or so years for say the 80's or older cars the replacement parts quality has been terrible and things like blower motors are a one size sorta kinda seems close enough to say fits all.  The replacements either don't have the correct motor or correct fan blade or correct fit to operate as designed which often means they suck more power than the originals did and this is often more than the circuit was designed to support when it was new.  Add 20-50 years of age to that circuit and demand more power?  Its amazing we don't have more literal meltdowns than we do get.

Anyways back to the relays.  The relay area is often one of the weaker links in the electrical system.  I say area because sometimes it doesn't seem to be the relay itself that actually started to overheat, its often the socket.  Once anything starts to get warm its at first a fairly slow at first chain reaction till something completely fails.  If you do find signs of relay issues you need to very carefully inspect the socket to make sure its not going to damage a new relay. 

These older relays are often but not always fairly easy to open up for a closer inspection.  One thing to look for is are the blades with the contacts all standing straight and parallel and square in relation to other fixed components?  I have had relays that overall visually look good but then I notice one of the blades isn't quite straight.  You then start looking really close and notice that the plastic base is maybe melted slightly and let the contact move out of alignment so its maybe always making contact or makes contact from very slight vibrations or slight electrical leakage that normally would not activate it.    

[motard]

I changed the relays to new ones when I first encountered the issue. They did not solve the problem. Of course I am not sure if I have the terminals connector connected to the bottom of the top 5 prong relay correctly. The bottom connector connects to prongs #4 and #5. One wire in the connector is a hot wire and one wire is a negative wire. I connected the hot wire to #5 prong and the negative wire to #4 prong. Is this correct?

[motard]

The AC works and the clutch engages. However now it has leaked out the freon.

["Cadillac Kid" Greg Surfas 15364]

First things first. Does your system have one or two relays?
Greg Surfas

[motard]

It has two relays. A 5 prong relay and a 4 prong relay.

["Cadillac Kid" Greg Surfas 15364]

Are you saying that he wires are not grouped in connector?  I would strongly suggest you get a factory service manual. On each of the relays there are two terminals for the relay (engagement) coil. One relay is the "lo speed" relay, energizing the fan (low) circuit when the ignition is on. The second is the "auto" relay, engaged when the system is on Low-auto-High- defrost.
Greg Surfas

[scottsdaleaz]

From 1975...  unplug the ATC programmer or ATC Control head to split the problem area?

[Chopper1942]

There is a short to B+ on the blower motor circuit. Without a wiring schematic it is a crap shot to diag the circuit. If I remember correctly the B+ to the high blower relay on most GM vehicles were either red or orange and it it usually a 12 or 14 gauge wire. Trace the wire from the blower motor back to the relay it is commected to. If it is the 4 pin relay it probably has 2 heavy wires for blower B+ and 2 smaller wires, a control for the relay and a ground (?) for the relay With a test light, see how many of the wires will light the test light when you back probe the connector or terminals. One of the heavy wires may be hot at all times. If one of the small wires lights the light, disconnect it from the relay and see if the blower shuts off. If so, trace the wire to find where it is shorted to B+ or the device that is supplying B+ on the circuit.

the 5 terminal relay can be tested similiar to the 4 pin.

If possible get a wiring schematic. I will see if I still have an HVAC resource manual at home when I get there. If so, I will post again later.