Heater fan comes and goes

[RedBird64]

Odd thing happened while driving the other day. I had the fan on "2" and after short time, it either dropped to "1" or quite altoghether. I didn't really notice it until I heard it ramp back up to speed. The failure mode wasn't reproducible.
I'm a retired EE and I know there are all kinds of things that can cause this but is there a part that commonly fails? I noticed that vendors sell a replacement fan speed switch. Seems like any repop part they sell, I will eventually need..
Anyone else experience this?

Thanks,
Scott

[paulr]

Failing resistor and/or wiring/plug?

[jtschug]

Switches certainly fail, but I think the resistor fails more often. Then again the motor can't be counted out either. Most of the wiring problems I have had were the result of improper repairs, or under the hood where the looms are exposed to high temps. So if you see black vinyl tape in the fan circuit, start there.

[Terry64HT]

jtschug makes a good point about the motor, especially if the little hoses for the cooling are not in place. Air is supposed to be drawn from under the dash to cool the fan motor, but if the little double 90 degree hose is missing, dirty air from the engine compartment is drawn into the motor. That can gum things up enough that the motor will change speed as it heats up and cools down.
Terry
64HT

[RedBird64]

THanks everyone. Sounds like pretty much anything is suspect.
Terry, I have a non-AC car, do they have the cooling hose(s) thing like the AC cars do?
The heater plenum is literally the only place in the car that I have not delved into. I'll pull the resistor pack to see what kind of shape it's in.

Scott

[paulr]

jtschug makes a good point about the motor, especially if the little hoses for the cooling are not in place. Air is supposed to be drawn from under the dash to cool the fan motor, but if the little double 90 degree hose is missing, dirty air from the engine compartment is drawn into the motor. That can gum things up enough that the motor will change speed as it heats up and cools down.
Terry
64HT

Heat-only cars won’t have the engine bay vent hoses, which Scott drives.

EDIT: sorry, should have read Scott’s post.

[Terry64HT]

I didn't know it's a non-A/C car either. I know the fan motor protrudes into the engine bay for both types, so I assume they all use the cooling hoses. Can't say I've ever looked. Perhaps a non-A/C owner can help out.
Terry
64HT

[RAVEN]

On Non A/C cars the motor is installed inside the heater box and does not protrude into the motor area. It is hidden behind a blank cover on the firewall. The Non A/C car heater motor also does not have cooling hoses. It is a totally different looking motor.
I would question the heater motor bearings possibly seizing, causing them to drag, which in turn increases the electrical load and possibly causing the circuit breaker in fuse panel to open then reset in a repeating action. Making the fan oscillate.

[RedBird64]

There's not much to the fan cover. Kind of a pie pan thingy without any hoses (see pic).

The bearing idea Raven wrote of is intriguing. The fan motor doesn't seem very stong. It doesn't ramp up real fast like a modern car but then again, I don't think it ever has. Could be worn or rusty though.
I think I'll throw a charger on the battery, switch the ign to acc. and run the fan and see if I can get it to act up. Hopefully I can catch it in the act and troubleshoot it. Probalby pull the fan motor just to inspect it.
Thanks for all the input.

Scott

[Terry64HT]

Thanks for the info. Every day I learn something here.
Terry
64HT

[paulr]

It doesn't ramp up real fast like a modern car but then again, I don't think it ever has. Could be worn or rusty though.


Scott

It should.
(That sounds like a resistor issue.)

[RedBird64]

It doesn't ramp up real fast like a modern car but then again, I don't think it ever has. Could be worn or rusty though.


Scott

It should.
(That sounds like a resistor issue.)

I've never even unplugged the resistor so that's another good place to look for badness.

All I can find are cheap parts; both the resisitor and motor are only about $20 each. Gotta wonder what you get for that!

[sseebart]

Not to hijack, but what's that nut on top of the valve cover connected to?

~Steve

(Ok, I that's totally hijacking.)

[RedBird64]

Not to hijack, but what's that nut on top of the valve cover connected to?

~Steve

(Ok, I that's totally hijacking.)

I once had a PCV valve there so it's a one of those rubber plugs that you tighten down and they swell to seal the hole.

Scott

[RAVEN]

Scott, it has almost been two months since you posted this topic. What was the fault and correction to solve the problem?