[Dusty82]

I have a question for the electrical gurus in the forum. Please be patient with me here, as this is kind of hard to describe...

My '82 El Camino daily driver has a problem with AM radio interference from the heater blower, but this interference is a bit strange. When I first start the engine and turn on the heater/defroster, I turn the heater on HIGH. There's a slight hum in the radio, but nothing that I can't live with. As the engine warms up, the hum grows louder, until it gets to the point that I can't hear the radio. I discovered that by turning the heater fan down to the next lower speed, then switching it directly back to high, the noise stops completely and immediately. I drive 28 miles to work, and I have to repeat this probably 5 or 6 times along the way. Also, if I try to run the fan at anything except high or low, the noise comes right back, but stops as soon as I switch it back to either high or low.

My question is, is this a problem with the blower motor itself? The heater switch? Is there a resister in there that has burned out or something? Gremlins? Demonic possession?

Any help you can give me in this regard will certainly be appreciated.

 

[matt167]

alternator is going bad, replace diodes in alternator ( 1 way check valve that makes the AC current DC, when they go bad you get this interference ) or replace alternator

 

[Dusty82]

alternator is going bad, replace diodes in alternator ( 1 way check valve that makes the AC current DC, when they go bad you get this interference ) or replace alternator

Wouldn't that cause interference all the time, and not just when I turn on the heater? If I'm driving with the heater turned off, there's no interference at all.

 

[docvette]

Doc here, imp:

AM radio is a "noise Catcher" after all..it is nothing more than amplified Spark , with audio information compressed within the carrier Wave..sent through the air..almost any spark producer will cause noise in an AM unit..

That being said..Does this noise sound like a "Whine" and is it RPM conforming?

If it is..It may not be the heater at all, but the HEATER DRAW..on the altenator..If thats the case, you have some diodes failing in the Alternator, that need addressing.

If it is NOT the high draw and in fact, the heater motor, you may have a small leak from the core, into the motor (Noise gets louder when warm..) and the armature and brushes are "Sparking" pull the motor, inspect for rust trails and clean the armature and replace the brushes..

Disassemble the end bell from the motor, and remove the armature (the squirrel Cage must come off) and place it in a vise, use a fine croakas or Emory Cloth around the copper pickups, and sand until Clean and smooth..work down any pits..next clean out the pad insulators (between the pads) with a hobby knife or box knife...(Talaban Passport.. )

Next get a new set of brushes, reinstall the new brushes on the end bell, (or if there is enough brush left, reuse them..) and assemble the whole system.

That should quiet it all down, If not you can try a noise filter on the radio power wire, (get one at the local auto audio shop) that will also help..

Doc imp:

 

[Dusty82]

Doc here, imp:

That being said..Does this noise sound like a "Whine" and is it RPM conforming?

Doc imp:

No, this is not a whine that changes pitch as the engine RPMs change. This starts out as a slight hum, then increases in volume until it's a loud buzz that stays at the same steady pitch no matter how fast the engine is turning. I've heard the whine you're talking about in another old truck, and this isn't it.

I'll check out the blower motor this weekend when I can tear it down. Thanks for the tips on what to look for once I get it apart, Doc.

The thing that I thought was strange about it is there is no interference or noise at all with the heater off or the fan running on LOW. The noise is loud enough to drown out the radio with the fan running at the next two speeds, and it comes and goes as I described earlier when I run the fan on HIGH.

Lord, I hate electrical gremlins... ain:

 

[docvette]

No, this is not a whine that changes pitch as the engine RPMs change. This starts out as a slight hum, then increases in volume until it's a loud buzz that stays at the same steady pitch no matter how fast the engine is turning. I've heard the whine you're talking about in another old truck, and this isn't it.

I'll check out the blower motor this weekend when I can tear it down. Thanks for the tips on what to look for once I get it apart, Doc.

The thing that I thought was strange about it is there is no interference or noise at all with the heater off or the fan running on LOW. The noise is loud enough to drown out the radio with the fan running at the next two speeds, and it comes and goes as I described earlier when I run the fan on HIGH.

Lord, I hate electrical gremlins... ain:

Doc here, imp:

When the motor is on low, It is pulling LESS current, and producing less sparking..is probably why it acts up under high speed only.

Forgot to add..if the motor does show water damage, fix the heater core (or maybe hose leak) also..or you'll have trouble again.

Doc imp: