blower motor

[73SWBBB]

So it's 93 degrees here today and about time to hook up the A/C the supposedly worked but just had the belt removed for performance reasoning. Whatever. The first thing I'm getting hung up on is the Blower motor not working correctly. This truck does have an aftermarket harness in it but I've been able to figure everthing else out so far by bouncing some ideas around on this site so lets see if anyone can help me out. I read for power going to the blower motor and have 11.8 VDC only in high position. It is millivolts in all other settings. So I pulled the blower motor and replaced it after testing it on the battery and getting absolutely nothing. After reinstalling I've still got nothing. Doesn't work in any setting. So I've come up with nothing for a schematic on this and was hoping someone may be able to enlighten me? 1973 454 with factory ac.

[73SWBBB]

I've also found a single blue wire coming from the blower motor transistor going nowhere. It is also a live wire so my guess is it could be useful if it were in the right place. Any schematics out there? The shady haynes manual only has 1989 and later.

[beastie_3]

schematics are in the tech section




Wiring Schematics

[DnStClr]

It sounds like the motor is getting voltage , so the next place to check is the resistors, which are located right above the blower motor. I had a pic around here somewhere that I posted awhile back..  and of course, you want to take an ohms reading at the switch too, in order to check the continuity of the 3 position control switch on the dash.  Here's the resistors- the pic is for a 1978 truck, but it should look the same as yours.



edited for spellin!

[73SWBBB]

Thanks, I have a new resistor and relay on the tool box right now but I am still having difficulty locating the proper schematic. The one guy that had an ac problem and was supplied a schematic in the tech section is the closest i can find but the blower motor relay has the prongs in different spots so im currently reading out the relay to figure out which post is what but it would be nice to see a schematic with the actual relay i have. The colors on my harness dont match up but Im bound and determined.....its hot!

[73SWBBB]

So I've converted to a newer style relay thanks to the junkyard so I could convert my truck to the only schematic I could find. Sounds silly but it was already torn apart pretty well and long story short I have a working blower motor, sort of. It works in low speed no matter what the setting. I also nabbed a blower resistor from the junkyard just to have another part to throw at it in case it happened to be that. The blower resistors I have are both used but produce the same outcome. The only other thing that has caught my eye was a single yellow wire coming off of the selector switch assembly, its riveted to the top if the vent/ac/selector area. It goes nowhere and just hangs there with a connector end looking like it should be plugged in..... I get just about 12 volts in all settings to the blower motor which would make me think it would be in high all the time but I'm still learning here. Any pointers would be greatly appreciated

[78 Chevyrado]

Check your relay, no matter how new it is...

I had a problem with mine, the relay (stock type) that everybody, including GM sold me would burn up instantly on first use.  It turned out to be a resistor between two of the terminals under the cover had fried.  My OE relay did NOT have this resistor, so I bought another new resistor and snipped off the resistor and it works very well to this day.   Just pop the cover off the relay and if you see a burnt resistor, get another new one and snip that resistor out before you try it.

[73SWBBB]

So after really ensuring I had a proper ground on the blower motor housing (which could have been the main issue here all along to be honest) and replacing the blower motor relay with a new. I now have every speed except for high. So my guess is the resistor itself is the culprit? I am going to read some more out with the meter cause Im pretty sure none of the local parts places have them in stock. But Ill check back here again before I go order it just to see if anyone can help me with the new gripe. Also, anyone know whats up with the yellow wire i wrote about earlier?

[DnStClr]

Here's a similar thread with a schematic from 67-72 chevytrucks website. It shows a yellow wire going to the blower.

http://67-72chevytrucks.com/vboard/showthread.php?t=392034