Heat Blower / Fusible Link / Electrical Help (1 Viewer)

[Rube]

Trying to chase down heater malfunction and after trying to wrap my brain around the wiring diagram, I am now thinking it may be the "Red" portion of my fusible link. Please point me in another direction if this seems ridiculous or if I am way off. Photos of wiring diagram to follow but here are some of my symptoms.

1. No heat blower motor. Replaced CB & motor itself checks out.
2. No carb fan.

The only portions that don't seem to add up are the alternator (voltage does fluctuate some) and ignition (starts but takes a few cranks).

Am I way out of line in this train of thought? PO replaced the stock fusible linkage with some aftermarket wires but none look fried (to my virgin eyes).

 

[86aggie]

Do you have power at the blower and at fan?

 

[Rube]

I’ll check it tonight when I get back home

 

[workingdog]

What are you suspecting about the modified fusible link?

So, do you have a fusible link anymore? Or are those just regular wires? I suspect the PO just removed it. Although there are a lot of people that like the fusible links on here, there are more modern options that you can use that are more easily replaceable and give protection (you might be without right now).

 

[Rube]

It’s replaced with fusible link wire, I was really wanting to see if my understanding of the wiring diagram made those 2 connections plausible. I can replace with more fusible link wire rather easily. The OEM connections have long since been removed.

 

[php74]

Don’t forget to check the blower resistor. Usually diagnosed by certain fan speeds not working.

 

[workingdog]

Yes, I don't see anything wrong with your reading of the diagram, but I'd suspect the fans first. But fusible link wires are notorious. Some people slice in regular wire just to figure things out, and then go back to fusible link wires when they have everything working.

 

[Rube]

Don’t forget to check the blower resistor. Usually diagnosed by certain fan speeds not working.

No fan speeds working but fan blows when hotwired to battery. Forgot to check for power getting to the fan which was dumb on my part. Carb fan was working but hasn’t since the blower fan quit which is why I thought it may be the fusible link but couldn’t explain apparent lack of symptoms from alternator and ignition which also share that linkage

 

[workingdog]

As php74 said, is the heater fan flowing when you hot wire directly to the fan? Or did you go through the switch (and the resistors)? What happens when you hot wire the carb fan? Is there +12 at the carb fan?

 

[Rube]

As php74 said, is the heater fan flowing when you hot wire directly to the fan? Or did you go through the switch (and the resistors)? What happens when you hot wire the carb fan? Is there +12 at the carb fan?

Heater fan blows when hotwired as does carb fan. Haven’t had a chance to check for voltage coming into either today but will tonight.

 

[Dr. John]

With NO fan speeds...and a fan that works when hotwired...I'd first suspect the fan relay.

 

[Rube]

So the saga continues. I have power to my heater blower motor 12v. Hotwiring the blower results in perfect function. Problem is when I plug everything up, the voltage drops to zero. Help?

 

[Dr. John]

Where are your meter probes when you show 0 volts?

 

[Rube]

On hot and ground wires going to blower fan

 

[workingdog]

So, through the switch? Can you test before the switch?

 

[Rube]

So, through the switch? Can you test before the switch?

I'll go back out later this week with the FSM in hand (should've done this before) and test it out. Thats my next guess though.

 

[Dr. John]

My current (pun) best bet is that you have a corroded connection at the switch, relay, or resistor pack. Just enough current is getting through to show 12v on the meter, but with the motor in the circuit, not enough current can flow and voltage (and current) drop to near zero. Resistor pack is easy to get to...it inserts into the air plenum, under dash, left side of the hump. 2 wires, 2 screws.

 

[Rube]

Thanks for the help. I'll take some more time in the next few days. Hopefully be able to post up a solution.

 

[emac]

The problem on my heater was a dirty switch and a bad relay.

 

[Rube]

The problem on my heater was a dirty switch and a bad relay.

If needed, is the relay still available and if so, what is the part number?