Hello to all. Have been surfing the forum for years. So much great info. Newbie question. I have a 71 442 non ac car. Heater fan motor has worked fine for 15 + years. It is now blowing the 25 amp fuse in the fuse box. With the switch in the off position it blows the fuse when the keyed ignition is turned to on. Have gone over all the chassis grounds and disconnected the power going to the blower motor. Any ideas?

 

I believe there is also a ground wire located on the blower motor. Have you cleaned that wire, sanded it down for good contact?

 

Here is a slurry of good threads to review from a quick CO thread search.

https://classicoldsmobile.com/forums...archid=5391081

 

Thanks for the ideas.. I've been searching the threads for weeks. Nobody seems to have the same problem I have on a non ac car. It still pops the fuse with the motor disconnected. From the assembly manual it looks like it goes from fuse panel, switch, resistor then motor. Or did I miss something between fuse box and switch?

 

I haven't had to troubleshoot this particular issue w/ my '71 CS, I'd have to review the wiring diagram; but two things do come to mind: (1) Isn't there a relay between the fuse panel and the switch or a relay somewhere in the mix; and, (2) there does exist the possibility the blower motor has tanked. One of the chaps (matt or someone) mentioned to review/visualize the nature of the fuse after it has blown proposing if there exists a large blob of molten metal towards one end of the fuse it suggests a rapidly blown fuse where amperage draw has immediately increased and blown the fuse rapidly and the other was if no blob was evident it would indicate a slow/intermittent amperage draw possibly resulting from bad grounds? Did you review the wiring diagram in the CSM to see if a relay can be found?

 

Sorry, I'm bad. You did state the resistor, which would have a relay contained w/in the resistor. I would suspect the first thing to try is to replace that relay (transistor). These old buggers are definitely prone to having relays fail after 50 years. I'm looking at the wiring diagram and it appears the only relay (transistor) is between the blower switch and the blower motor. I don't think you missed anything. Try a new relay and give that a shot.

 

Thanks Chief. The fuse blow is rapid. Instantly fries fuse as soon as ignition is turned on. I guess I will disconnect switch and see if it still does it. Than I will have to start throwing money at the cheapest things first. With how the fuse blows it seems like a dead short. All other electrical on the car operates perfect.

 

Well, the first thing would be to simply remove that relay from the mix, replace the fuse, and then see if the fuse blows again. If the fuse doesn't blow I'd suspect the relay is toast. If the fuse still blows, I guess I'd run backwards up the line & disconnect the switch to see if the fuse still blows. Hopefully, removing the relay from the mix and inserting a new fuse and hopefully not seeing the fuse blown you can get to replacing the relay. Sometimes those ends and even inside the relays get really corroded. It may have shorted out on its own and took the big dump.

 

Note to write down where each wire connects to the poles on the relay so you know where you are on hooking up another relay and ensure you get the correct relay - there are so many of them out there. GL

 

If there is a blob on the end of the broken fuse strip inside the glass it is a from too much current draw over a longer period of time. Its from the current slowly building up enough heat to melt the fuse strip from a worn out motor or bad connection.

A direct short to ground will cause sudden failure of the fuse strip without enough time to melt/form the blob.

In this instance put a test lamp across the blown fuse, it should light. Unplug the blower switch and other items until the light goes out indicating the short to ground has been interrupted. My GUESS is that the blower switch and/or the connection at the switch has failed.

Were any other repairs done just prior to this happening?

Good luck!!!
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Thanks Sugar. It was actually you I had read earlier suggesting how the fuse had blown visually. That's good information. I couldn't recall exactly how you stated it and I actually had it backwards (figures).

 

Electrical system is original and unhacked. No recent repairs. With motor and resistor behind glove box disconnected fuse still blows. No ball on end of strip it is an istant fry. Put the test light on the fuse and it lights. Next is blower switch. Any tricks on removal. Haven't had a dash apart in 30 yrs. Am I missing anything else?
Thanks to all!

 

I'm armchairing this from my desktop PC. I've opened the '71 Factory Assembly Manual and created a blow up of the Heater Control Assembly. It appears there is a Alan screw or straight tip screw holding the ****. Then there are a couple screws which are accessed from the back of the control assembly to remove the switch and/or the wire from the switch. HTH

 

Thank you.
I just had out my old faded copied assembly manual in a 3 ring binder. Was just trying to blow it up with a magnifying glass. Lol

 

NP. I have new hard copy 3-ring binder edition and a digital pdf version which makes it nice for assisting others on CO.

 

I might suggest grabbing a mirror and flash light to visualize the work area behind the control assembly to gain a perspective.

 

I don't think you're missing anything. With an instant fry something is directly shorted to ground, that makes it a little easier to find. Keep unplugging things until you find it.


Good luck!!!
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Leave the blower motor disconnected while unplugging other connections. Try moving switches, levers and wires while watching for the light to flicker, dim or go out completely.

Good luck!!!

 

Problem solved. Traced the power wire from the fuse box to the fan switch and found a small broken spot in the casing on the wire where it made a bend. At that exact point it was touching metal and dead shorting. I think it was a case of 50 yrs of rubbing. A little tape and a re route and I have my fan motor back with all speeds.
Thanks to all!!!

 

Glad you're riding tall in the saddle again. You might consider zip-ties. I love zip-ties to keep wires out of areas they don't belong.

 

Nice work, you found the real problem vs. winging aftermarket parts at it to replace good originals.

Ride on!!!