HVAC blower issue

[jrbarrie83]

When I bought my '83, the blower did not work.  The guy had a jump wire attached to the large red wire going into the relay on the a/c box that he would connect to the large purple wire.  This, of course, could not stay attached as it would run at any time (ignition on or off) and it would only operate at high speed.  My first thought was to replace the relay - still no change.  What should my next step be?  The mode selector lever works as far as changing which outlets the air comes from, but could it still be bad as far as sending power to the blower?  I can't think of any other way power would be interrupted.  I need to replace the heater core and dash pad ... and gauge bezel ... so while I'm at that I figure it would be best to tackle this issue as well.

Thanks all!!
Jim

[rich weyand]

Could be either the blower motor switch or the blower motor resistor.  I don't think there is a relay in circuit with the blower motor.

See these pages:
upper left of http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_instrument_pg1.jpg
upper right of http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_V8_engine.jpg

[Jason S]

Just to be make sure of what you have, does your truck have/had factory installed air conditioning or is it a heater only truck?

[jrbarrie83]

Yes, it is factory A/C.

[Jason S]

The schematic listed above shows the wiring for a heater only truck. 

With a factory A/C system, there should be a relay in line with the blower system. It should be a two position relay; that is it will normally be in one position in all lower fan speed positions and route power through the blower resistor based on the selected fan speed.  When high speed is switched on at the panel, it will engage the high position in the relay and direct full 12v (bypassing the resistors) to the blower.

The relay should have a connection that runs to the battery junction block on the firewall (a larger gauge wire) in addition to the the wiring connect to it from inside the cab.

Your setup should be similar, but not exactly, to the photos/schematics in the post below:

http://forum.73-87chevytrucks.com/smforum/index.php/topic,1944.0.html

You can get the manuals and schematics for your '83 truck, under wiring manuals here:
http://forum.73-87chevytrucks.com/smforum/index.php/topic,25639.0.html

If there is not power going to the blower relay from the blower motor switch, then there may be a problem with the wiring to the relay or it could be a defective blower switch or simply a blown fuse.