Turtlerok

Thanks to everyone who contributes here, without the forum I would be further behind in my troublshooting. I have a 350, '75 coupe and still in the learning phases of taking care of the vette.

I notice that about 6 months ago, my heat/air was not working, or more correctly stated I was getting no air flow out of the vents. So I went ahead and brought a new control switch that mounts in the console on the floor... (i couldn't read the letters anyway). Still no airflow.

So then I was reading about the AC relay, so I went ahead and bought that like 3 days ago. After replacement, I now was getting air out of the vents except for the high speed, which if I remember never had worked.

So I went ahead and check the inline fuse which was blown, so I replaced that with a new 30 amp fuse and tried again. I still was not getting air flow when using the high speed, and my fuse had blown once again.

So now I'm trying to figure out where do I go from here to troubleshoot. I think I read about a high speed relay, where would that be? Or am I way off base... any help would be great!

goinbroke

That relay is a small rectangular silver box in the engine compartment mounted (usually) near the blower motor. There's a pic of it in this thread from the archives. http://forums.corvetteforum.com/show...t=blower+relay

Turtlerok

Yep, I know where that is, I'll see about getting a replacement or at least take a better look at the contacts and connector. Thanks

Turtlerok

I took a look at that relay in question, the insides look brand new, or like it never was used. The connectors look good. But I do see a little black wire with a electicial connection plug that doesn't some to go anywhere. Its come from the wire bundle from the starter. I don't see anything close where it plugs into so anyone has an idea, I'm open.

Whatever is happen it's blowing out my fuse so thats telling me there is a high load somewhere? Wouldn't think it'll be because of a wire not connected?

Thanks,

chris75stingray

there is a single wire that plugs into the blower from the engine side. it's kind of tucked up in the right fender by the cowl. (is that the wire you are refering to?) that runs the blower at high speed . mine came disconnected once and the blower didn't work on high.

Turtlerok

I looked under the fender I do see a black wire that is connected to the blower. The bundle that I see coming from the starter -I just noticed that there are two small gauge wires, the one is connected to the high speed relay the other looks like it goes no where.

By looking in that are I see no place where that wire could connect, so maybe I need to keep in mind that bubba that work on it before. Maybe this is just an extra... anyone know what voltage I should find on each of the high relay connections wires or just how to troubeshoot this. I just I could see if this is just another ground wire using a voltmeter.

Once again any direction would be great.

AimHigh

Thank God for guys with the same problems....I too couldn't get my blower to work on high and have been too busy to figure it out.

Great post,,,,I followed your directions and all is good now!
cheers

r/wdd

goinbroke

According to the service manual (74), if you keep blowing the 30 amp inline fuse it indicates a short circuit in the wire (orange?) between the junction block and the relay.

Goes on to say that short circuits can be intermittent.....move harness around to re-create the the short. Watch and listen for arcing.

RunningMan373

One check you can do to isolate is to take the connector loose from the bottom of the blower motor relay, if it still blows fuses the problem is in or after the relay, if not, it's in the harness, or up to it. It doesn't take much contact over time to wear the insulation to a short. C.

LYLE

That little black wire is part of the smog/TCS not the heater blower.

Turtlerok

I'm not familer with that (smog/TCS), what is it and should I be concern there is nothing to connect? It seems like the small balck wire is a ground connection.

Thanks for the help everyone... i'll see what happens after unplugging the high speed blower relay.

moosie982

Please, Please, Please, dont do this, but there was this old mechanic at a Chevy dealer where I worked (parts dept.) who was aces at finding shorts and related electrical problems. His act was to put a small screw into the fuse box to take the place of the fuse that kept blowing and look for smoke, thats where the short originated from , he had to be quick or else he'd have to replace more wires then he wanted to or quite possibly set the car on fire. He was the exclusive electrical troubleshooter for many years. Good Luck,,, Peace, Moosie

davidpjr

I have a 74. I have checked the fuse and replaced the high speed switch, the one mounted on the firewall. It still does not work in high. When I move it to high and back to low, I hear a click but nothing happens. Does anyone have any other ideas?

RunningMan373

what rating fuse did you use on the replacement? The original was 20 or 30 amps, a 7 or 10 amp will blow out. Does the blower work all all the other positions up to high? If it does, then the problem is still most likely the power being delivered to the blower motor high relay. recheck the fuse, then unplug the connector from the bottom of the blower motor relay the one pictured below, and get a voltmeter. you will be testing the orange wire for 12V. It should be hot (at 12V) All The Time, even with the engine off and key out. It is the feed for the high speed relay. The relay clicking means that it should be working. At this point I would still suspect the fuse.

davidpjr

Well, thanks for the suggestions. However, it seems that the fuse on my 74 is not under the dash where I suspected but between the firewall and front tire on the drivers side. Apparently it is an inline fuse and that is the one for the high speed. The low speed fuse is under the dash. Perhaps I missed that tidbit in all of this but if anyone is still looking for the fuse, that is where it is at.

1975Stingray

Great post and responses! I too have been diagnosing the high speed blower issue. Looks like Inline Fuse is good and I can get the High speed function to work when I jump the purple wire. I thinking its the relay now, but not checked for 12volt wire for consist power. Hopefully will check tonight and will order a new relay today. Thank you for all the responses on this thread, helped me out a lot!

L-46man

Reminds me of the Pick-up truck owner who replaced the barrel fuse with a 22LR bullet....AND you KNOW what happened!

Be patient...follow the wiring diagram...get your crayons out! Get out the volt meter! Get out the test light.
Check the grounds!

Good Luck.

Unkahal

Argentimage

Good friend came by with his 76 earlier today, same thing, no high blower, but he has the lower two speeds.
inline fuse checks OK
Ground under dash had been removed and redone,
new console switch, it works in the first two but not high blower, via other similar very old threads, how can this be a blower motor issue If its spinning on the first 2-3 speeds?

VERYSOON

Turtle
Yes, this is how to check your high speed relay. Pull the connector on the relay and jump the orange wire and purple wire. Your blower should turn on AS LONG AS THE GROUND IS GOOD!
I had this problem 3 days ago. When the blower did not turn on I assumed motor was dead so I removed the blower motor. The ground checked good with a volt meter test but it wasn't good enough to make the motor run!! I cleaned up the ground where it attaches to the blower casing and it now blows like a sumbitch!
It is a cast iron bitch to get this out of a 69. You have to disassemble the squirrel cage to maneuver it out in two pieces without dismounting the compressor!!

The triangular shaped plate with 4 wires going to it located on evaporator box is a resistor setup for the fan low speeds.

4 hours work and a little blood but at least I know I have a numbers matching blower motor! :-)

Hope this helps all. Check and recheck the ground first!!!
VS

Ben Peska

My 1987 Corvette AC/heater blower motor is not working on high .... fuses are good it works great on the first three settings but when you turn it to high I get nothing ...anybody have Any suggestions ?