Blower Fan 4th/High Speed

[Les W.]

I hope someone can help me out. My LT-1 w/AC blower fan quit on me in the high speed or fourth and last notch to the right. All other speeds work fine. In one of the threads I found that a fuse located close to the alternater on a red wire could be the problem. I checked it and it is not blown. In the 1972 service manual on page 1A-52 @ the lower right under FUSES it says a second fuse for high speed is located between the horn relay and AC relay. Where is this fuse located or is it the same fuse I already checked???

[John H.]

Re: Blower Fan 4th/High Speed

Where is this fuse located or is it the same fuse I already checked???

Les -

I believe that's the fuse you checked - it's the only in-line fuse shown on the '72 A/C wiring diagram (it originates at the screw terminals on the horn relay). Do you have power at the other end of that wire in the connector at the blower relay?

[Craig H.]

Re: Blower Fan 4th/High Speed

Hi Les

From my understanding the fan is powered ....

- in its lower speeds by power that has routed through the selector switch then via the resisters (to limit current and speed)
- in the high speed power flows through the selector switch to a relay on AC box that then switches to allow direct current from the fuse relay to the fan.

So if its not working its either the fuse on the direct power wire, the relay or the switching power from the console switch.

Easy to check with a multimeter at the relay.

I think its dark blue from the switch to the relay and Orange from the horn relay. Also check the relay is properly earthed as that will stop it working.

My relay was baked beyond working so was the culprit.

Craig

[Robert S.]

Re: Blower Fan 4th/High Speed

If the in line fuse is ok then I would suspect the high speed relay. I had this issue on my 74' with AC. I took the cover off of the relay (which was relatively new and the high speed function used only a few times) and found that the points inside were pitted and that the points did not line up (mechanically) very well. I removed the relay and dressed the points with a fine file and aligned the points so they contacted correctly and the high speed blower was back in operation.

[Les W.]

Re: Blower Fan 4th/High Speed

John, Craig & Robert,

Thanks for the response. I will spend tomorrow trying to run down the problem. I have a voltmeter and I am not too knowledgable on how to use it but I am sure I will be able to work it out. I hope the problem is the relay. I assume it is the silver looking box on the outside of the AC housing. I will also check the power going from the fuse orange wire to the relay.
Les

[Robert S.]

Re: Blower Fan 4th/High Speed

Yes the relay is the silver colored box you are describing. Replacement relays are readily available in case you want to just change yours out. In my case I was curious why a relatively new relay would just stop working. After I took the cover off of my relay I reinstalled it. I could see the points close when I put the switch on the high speed position so it was clear to me that I had an issue with the points.

[Les W.]

Re: Blower Fan 4th/High Speed

Robert, Thanks for the confirmation on the relay. I take it you had a bad set of points even though they made contact they didn't make a good connection? I'll work on it today and let you know. Les

[Robert S.]

Re: Blower Fan 4th/High Speed

Yes, the points have to carry the high current flow of the high speed position. I assumed (afterwards) that the points not making good mechanical contact led to point pitting and then an interruption in current flow.

[Les W.]

Re: Blower Fan 4th/High Speed

Robert, the emery cloth did the trick. Thanks for the information. I was cocerned that the motor may have been the problem. Thanks everyone!! Les