Radio interference issues

[FRANKENTRUCK]

I have an AC Delco factory radio in my truck that I bought and installed myself. For some reason when I turn on the heater fan the radio has electrical interference in it. Is there some type of sound filter that I need? Also this mystery box (see below) is attached to my radio wires in the truck. What is it for?

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[jo89k5]

The noise in the radio is most likely because of a bad ground, double check the ground wire for the radio, if that is good, check the ground wires under the hood.

As far as that box, can you get a clear picture of the front of it where the markings are.

 

[FRANKENTRUCK]

I am unable to get a clear picture but the top numbers are 1247314 and the wires on the bottom are labeled 1 through 10. It seems to house speaker wires including one that had a rubber red cap on it for a dash speaker that my truck has never had.

 

[chengny]

The radio is probably not the problem.

The RFI is only present when the HVAC blower is activated ( and varies in pitch with blower speed), right?

Given that, it would seem to me that the blower motor is causing the RFI . This could be caused either by a poor ground connection or internal arcing across the commutators/brushes. The radio is just picking that signal up.

You could install a filter in the hot wire to the radio - just snip & strip the wire and buttsplice it in - or you could check and repair the root problem - i.e. the blower motor.

Grounding:

If you have A/C there is a heavy gauge black wire that runs from the blower housing to a bolted ground connection at the firewall. Release the connection, clean the threads of both the bolt and the internal ones on the firewall - clean the connnector faces as well. Secure the bolt tightly.

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If you don't have A/C the motor is grounded through the fan casing. Pull the motor and fan assembly from the housing by removing the 5 little bolts around the perimeter. Clean the flange facces of both the blower housing and the motor casing. Clean the threads of the fasteners as described above. Reinstall and make up tight.

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If that doesn't help, the probem is sparking across the commuator bars and brush faces. It is a simple job to clean the commutator and undercut the micas.

Check the grounding circuit first and see what happens.

 

[FRANKENTRUCK]

***update***

The radio interference is also present sometimes when the gas pedal is pressed with no fan running. I am opting to go with the radio condenser thing to stop this. But which one do I use? The radio came out of a year-unknown Corvette and some of these condensers seem to be year-specific. There are several types listed and I have no idea which to buy. I could kick myself, because just the other day I had in my hand the sticker that fell off my radio with the Serial Number on it! Now it is missing. Here is the radio if this helps...

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