Milest

The high speed fan just quit working over the weekend. I replaced the relay with no luck. where should I look or check first.

Car is 1972 L-48 with AC

Thank you.

Wrencher

I'll have to check my manual (which is not here at work...) and see, but I'm pretty sure there is an inline 30A fuse in the main power wire for high blower.
Funny, my hi-speed just quit yesterday as well, so when I look at it tonight I'll let you know what I find...

Hans

Jvette73

Follow the fat wire leading out of the relay. It runs across the fire wall to the other side where its connected to an inline fuse. Its the type of fues where the wire is attached to each side with a nut. Maybe that fuse is blown. Anyway, thats where the power for the high speed setting comes from. Trace it around and check for power with a test light.

30yr Wait

Funny..mines not working either...69 w/ac
do I have the same fuse?

Jvette73

dont know for sure..my 73 is that way, so I asumed the 72 might be the same way. Maybe not though. Easy enough to check anyhow.

Milest

Thank you all for the responce. I will have a look tomorrow and most likely find the fuse blown.

Wrencher

Mine turned out to be a bad connection at the relay. The hi-blower connector in the plug was a loose fit on the metal spade, so pinched it tight and now it works great.

Also, I put a thermometer in the center register just to get an idea how cold it actually got, and got a surprise. At idle or sitting still, it goes right down to 38 degrees, but as soon as I start driving it goes up to 50! So I'm guessing there is engine area heat bleeding in somewhere. One more thing to check...

Hans

dogboy

Wrencher: That was my problem also. I was getting 52 deg from the vents when not moving and getting more heat when driving . up to 60 deg at vents. I found that the entire seal was leaking and also some open rust spots at the bottom of the unit weren't helping that much either. I burnt that inline fuse also due to a bad connection. I eventually scraped the entire system & went aftermarket.

Wrencher

Good call, dogboy! I must have been asleep when I put the case back together after the heater core job. I forgot to re-seal the outside edge with that black tape goop! After tonight it oughta' work great...

Hans

Milest

I had a chance to check the fuse and it is fine. I have 11.8 volts on the main wire (fused) that plugs into the relay when the switch is on medium or high. Still no high fan. Any more suggestions.

Thank you

Taijutsu

PICS PLEASE! No one ever said I was the sharpest tool in the shed. My 74 w/AC has several electric boxes and relays. Elect is all magic to me. A pic would make things much easier. If this is a simple parts replacement, that I can do! HELP! TIA
Rick

Jvette73

Milest, So you have power on the fat wire going into the relay right? So then put switch in the high position with key on. Then check for power comming out of the relay. You got power going in, so you need to check for power comming out. Check the terminal that the other fat wire connects to at the relay. That other fat wire leads to the blower motor. If you have no power comming out of the relay there, either the relay is bad, or its not getting the signal to activate from the dash switch.


The way it works and why is this. To run the blower on high speed takes a significant amount of amperage. Too much amperage to be running it up under the dash and thru the dash mounted switch. So a relay is used to keep all the high amperage wiring in the engine compartment. There is a seperate wire leading from the dash switch to the relay. Its one of the thinner wires thats connected at the relay. When you put the dash switch on high, it sends a voltage signal to the relay. The relay then makes the connection to allow the high amps to flow thru to the blower. So the relay is a remote switch controlled by the dash switch.

Youve established you have high amp power to the relay already. Next thing is to see if you have the high amps comming out the other side when the switch is on high. One of the smaller wires comming from the dash switch should read voltage when the switch is on the high setting. That would be the wire that tells the relay to make the connection for high speed. So if theres no power comming out of the relay for high speed, Either the relay is bad, or its not getting the signal from the dash switch. Hopes this helped you figure it out. Its usually much easier to fix things when you know how they work in the first place.