79 Corvette = no blower
Thread Starter
Heel & Toe
Joined: Jan 2005
Posts: 24
Likes: 0
From: South of Houston Texas
79 Corvette = no blower
I tried to search this problem. My daughter says the blower works sometimes (this would make me think a bad relay). Only the red wire on the relay is hot with the blower on, nothing on the blue, purple, or orange at lo, med, or high. Am I correct in assuming that I need a new switch? And is there a way to run a hot wire to the motor to make sure? Thanks, Kathy
Advanced
Joined: Sep 2008
Posts: 62
Likes: 0
From: Rindge NH
Hi Kathy, don't mistake me for an expert, but I went through the same thing with mine. I did a lot playing with my multimeter and pulling of things. I would start with pulling the motor an testing it on another battery. I just ran some jumpers off of my car. When that worked fine, I tested the switch and it seemed OK. That lead me to your picture, the relay. I picked at all the connections and found little to no power going through it. It was a cheap part to replace. One other thing you can check is the unit that the wires go to from the relay. There are a series of springs under that plate that provide that speed of the fan to vary. They should be fine but it doesn't hurt to pull it and check/clean. I hope this helps, good luck.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I would start with checking the fuse in the fuse box. If that's good, check for power at the 4 wire resister in the bottom of the picture in the different switch positions. If no power there, then it is probably a bad switch. The relay is for high speed for the fan, if you get everything except hi, then I might suspect the relay.
Ps, I see an ungrounded wire in the lower right of the pic, these are very important on fiberglass cars.
Ps, I see an ungrounded wire in the lower right of the pic, these are very important on fiberglass cars.
Instructor
Joined: Jul 2008
Posts: 123
Likes: 0
From: Allentown PA
Mine is doing the same thing. It is strange because I also lose my wiper motor at the same time. I looked at the wiring diagram to see what was common between the two. It looks like they may share the same ground wire, (black wire that is by itself coming off of the wiper motor). I tried putting a jumper from there to a good ground point and the wipers worked, I did not check the blower. Right now both the blower and wipers are working so I cannot troubleshoot further until it fails again. I would not suspect the fuse if the blower works sometimes. If fuse blows the blower will stop working, period. I will let you know if I find the cause later. Hopefully this points you in the right direction. 
Instructor
Joined: Jul 2008
Posts: 123
Likes: 0
From: Allentown PA
Ok, I got my wiring diagram and looked at what you said again in your original post. You said the only hot wire is the red one. That may be a problem because if I understand the wiring correctly one of the other wires should be hot at the same time, either the dark blue one or the purple one. When the relay is energized it should switch to the other wire, (blue hot and purple cold, or vice versa). I suspect either a bad relay or the plug to the relay is not making good contact. You can try removing plug then sliding it back on, sometimes that is enough to clean the connection.
Last edited by Tom's 79; Oct 29, 2009 at 09:34 AM.
7th Gear
Joined: Oct 2009
Posts: 7
Likes: 0
I agree with Tom.
If fuse blows, the blower will stop working, period.
I would suspect a electrical connection is making poor contact also.
Using the wiring diagram, I would start cleaning connections. Starting with the grounds. Then working from the fuse to the fan.
I use a thin fingernail file. I cut one end of the file to fit inside a standard female spade connector.
Putting a little dielectric grease on the connections helps prevent corrosion.
If I still have a problem after the cleaning, then I start jumpering across components to isolate the problem.
If fuse blows, the blower will stop working, period.
I would suspect a electrical connection is making poor contact also.
Using the wiring diagram, I would start cleaning connections. Starting with the grounds. Then working from the fuse to the fan.
I use a thin fingernail file. I cut one end of the file to fit inside a standard female spade connector.
Putting a little dielectric grease on the connections helps prevent corrosion.
If I still have a problem after the cleaning, then I start jumpering across components to isolate the problem.
Thread Starter
Heel & Toe
Joined: Jan 2005
Posts: 24
Likes: 0
From: South of Houston Texas
I would start with checking the fuse in the fuse box. If that's good, check for power at the 4 wire resister in the bottom of the picture in the different switch positions. If no power there, then it is probably a bad switch. The relay is for high speed for the fan, if you get everything except hi, then I might suspect the relay.
Ps, I see an ungrounded wire in the lower right of the pic, these are very important on fiberglass cars.
Ps, I see an ungrounded wire in the lower right of the pic, these are very important on fiberglass cars.
Last edited by Kisam; Oct 29, 2009 at 10:38 AM.
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Instructor
Joined: Sep 2009
Posts: 135
Likes: 2
From: Waterbury CT.
When the blower ISN"T working, conect a 12 volt test light to a good ground and check to see if the light lights up when you touch the blower motor orange wire. if the testlight lights up your problem is the motor or motor ground. At low speed the yellow wire at the resistor block is hot. At medium speed check lite blue wire, & high speed the orange wire is hot. If there's nothing at the resistor block then I'd suspect the blower switch.
