Thank you Thomas.
I thought 3A was awfully low. Either I misread the 30 as a 3, or is it possible that the "C/Fan" is not actually the cooling fan?

Last night, after cleaning all the relay terminals and reinstalling, with the car running and up to temperature, I got 13V at the fan plug although the fan was removed. I've got a replacement fan motor arriving on Friday, and I will try to get to it either Friday or Sunday. Hopefully I'll take the car on a road trip Monday if I can get a cooling system that works.

For the sake of curiosity, I let the car warm up yesterday with a new temp sender until it began to burp into the burp tank, which was risky, but I wanted to know how hot it might have gotten in the past. It reached about 255-260 degrees, which means it has probably hit 260 degrees at least a couple of times in its recent life, although luckily the previous couple of owners barely ever drove it.

This worries me, but the car seems fine. Can you advise how scared I should be of that temperature? Is it a miracle I haven't warped a head, or is that just hotter than you would want to see on a daily basis?

 

I'm thinking you might have more than one problem with the fans. Did you find the wire to the dash gauge water temp? That won't effect the fans. There should be 3 water temp sensors, 1 on the right head for the dash gauge, one on the left head for the primary fan and another one on the intake manifold for the ECM that activates the fan at around 226-227 degrees and shuts off at approximately 200 degrees. The secondary fan should engage at 240 degrees or when the air condition is turned on. If nether fan is turning on there could be a problem in both circuits. I would say anything above 240 degrees is to hot, boiling over at 235 degrees with a 16lb radiator cap. could be an issue with he ECM temp sensor or the ECM, Prom maybe. HVAC should turn on ate Aux fan from the dash unless the a/c fuse is missing or it relies on the a/c freon pressure switch to activate. A manual would be helpful.

 

You do have the option of putting in the new temp sensor, running the temp wire to the relay or adding a new 30amp relay and attaching the fan and have it run on it's own system like you do when anyone adds a electric fan and simplify it.

 

Thank you Thomas, for sticking with me on this one! I figured it out.
The 3A "C. Fan" fuse on the fuse panel must be the relay trigger supply fuse, not the actual fan. That I suppose is handled by the fusible link. It faked me out initially, since my ammeter measured 3.2A at the fan plug. A fan motor should of course draw more than that.

After I replaced the fan motor and the fan relay I still didn't get it to spin, at which point I did some more digging and located the fusible link to find that it had previously done its job (partially). I had previously gotten voltage and a little bit of amperage measured at the fan plug, but the fusible link fell apart in my hands. The link in question was Fusible Link D, as near as I can tell (in case somebody else runs into this issue). I ended up taking apart the original single-pin plug on the end of the fusible link, and soldering in my own blade fuse holder. On the other end of the fusible link is an over-molded hard plastic joint. I cut the joint back until I found the metal core inside where the wires and the fusible link were joined. I soldered my new fuse wire to that, before covering it over with two layers of heat shrink tubing. I will include pictures if I get a chance.

Upon attempting to warm up the car, it wouldn't start. Once I was finished stomping around and cursing I dug back in and realized I had loosened/cut the supply wire to what I believe was Fusible Link H (fuel pump), which attaches into the same over-molded joint that Fusible Link D comes out of. I was pressed for time, so I used a T-Tap style bite connector to splice the Fusible Link H back to power supply. It isn't ideal, although it should work fine and it saved me from undoing everything I had just done.

After I got power back to the fuel pump, the car fired up and I had fan cooling! I did notice, however, that the fan came on immediately. I suppose maybe the temp switch for the fan is bad, but for now I will rely on the thermostat to keep the machine at no less than 195 degrees.

Any idea what fuse I should use in place of the new fusible link? I installed it with a 30A fuse, but I feel like that may be a little high. I think the fusible link may have been 16 AWG wire, so somewhere around 20 Amps? I'm curious if you've got any ideas, I couldn't find any current draw info on the fan motor.

With this polished up, I should be just about ready to start driving this thing regularly once I can get past the salad-shooter-tire-dilemma and if I can get a heater core in it. It badly needs a heater core, but that appears to have been well documented on here lucky for me.

Thanks again for the help!

 

Google AI says 16 AWG wire should use a 10 amp fuse and the wire itself would open at an estimated 117 amps in open air.

 

117 Amps sounds a little high, but a 10 Amp fuse to protect a 16 AWG circuit sounds right. However, the circuit is bigger than that, I believe it is 12 AWG (protected by a 16 AWG fusible link). I've seen resources that suggest a 20-25A fuse to protect 12AWG circuits, but thought maybe somebody knew how much the fan is actually supposed to draw. I think I'll probably put in a 15 and see if it blows, then go up to a 20.

 

12 AWG is good for 20 amps. I suspect that the melt current drops significantly when the wire is insulated.

 

The nearest I can find the electric cooing fan motor on average draws 20amps when running, I'm sure it's more at startup surge. HVAC units use a 30amp normally. I'm not a huge fan of fuseable links but they serve there pourpose on direct shorts.

 

You can try using a 20 amp slow-blow fuse if the startup surge is blowing the 20 amp regular fuse.

 

A slow-blow fuse is a good idea, that's what a fusible link is supposed to act as. The fuse block I installed in place of the fusible link is a blade fuse, so I'll have to find some slow-blow blade fuses.