Blower Fan not working

[induction]

Hi there,

I have a 1978 Sierra, and it's been stored for several years.  At first the blower fan (that's supposed to always run) was intermittently blowing through the floor vent as normal (all HVAC switches off), but now it no longer works, and if I switch on the vent fan, it doesn't work either.  Anyone have suggestions for what to do?  My cruise control used to work too, not sure if it's related to the blower motor not working?  Thanks!

[Irish_Alley]

check fuses and relays on the side of the evaporator core box

[induction]

I checked the internal fuse box below the dash near the parking brake pedal, and I didn't find any bad fuses.  I checked around the evaporator in the engine area, and notice a 2inx3in metal & plastic electrical module that's secured with 2 small bolts to the evaporator area with a few wires going into it with 1 wire leading to a capacitor (?) that's connected to the blower motor.  Is this the relay?  It has 1 hot wire going into it (red, and it always has electricity).  But when I switch the fan on, I don't get any voltage readings on the other wires.  I remember the blower fan being always on whenever the engine is started (right??), so shouldn't there be electricity going to the blower fan whenever the ignition is on?  Should I check anywhere else?

[Irish_Alley]

in the key on position the fan will be on. i would tap the relay and see what happens i think its what your talking about it should turn on to make it easer on you turn it on high first and with the key "on" so if it does work you will hear the fan come on

[Irish_Alley]

also the resistor is on the top of the box (looks like a plate with a pittail going to it the resistor is hanging inside the box while the relay is on the side

[DnStClr]

It sure sounds like the relay has stuck open. If the blower doesn't work after you tap on it, then it's probably not closing to send the signal to the resistors.
Here's a pic of the resistors


Which fan speed you choose determines which resistor gets "used" by the voltage coming from the relay. So the reduced voltage can then travel on to the blower motor


Since you have B+ voltage at the red wire going into the relay,I think Irish is right- it sounds like the relay is bad.
  New relay costs @ $16.00.

[induction]

Thanks Everyone, but no luck - I replaced the relay (wow, these are getting hard to come by locally) and removed/inspected/cleaned the resistor, but that has not helped.  Is it safe to say that the only thing left is the actual HVAC/heater control module in the interior (is there a name to this HVAC control module)?  I didn't find any bad fuses either.  Below are pictures from my truck.  Anyone have ideas?

[VileZambonie]

It won't work if you don't plug it in.

[ccz145a]

It looked plugged in to me.

[VileZambonie]

Did you check for B+ at the wire coming out of the relay?

[beastie_3]

Do you have power coming out of the control switches?


A side question, in his first and second pic, (with the relay, resistor and motor wire labeled) what is bolted to the fan motor? It is inline with the motor power wire. Its the metal cylinder part, after the rubber connection.

[VileZambonie]

Noise filter, that's why I suggested plugging it in "directly I should have clarified"

[beastie_3]

What does the noise filter do? Is that a similar issue compared to why you shouldn't run amp power wires along speaker wires, and such?

[VileZambonie]

RFI (Radio frequency interference) is usually caused by large moving magnetic fields (emi) electromagnetic interference. If you are running a cb or am radio it may be necessary to do everything you can to reduce it. Crossing or twisting wires helps as well as filters etc.

As far as checking any malfunctioning electrical circuit, generally you want to start at the source of the trouble. In this case the blower doesn't work so you should start right at the blower. Is there B+ at the blower? How about before the filter?

[induction]

Bear with me guys, here's what I found:

1-a direct wiring from relay to motor doesn't work (regardless of interior switch setting)

2-confirmed again that the red wire is B+ (always hot)

3-There's 5 pins on the relay, so red is B+, purple goes from relay to motor, black is ground (?), and that leaves 2 more wires that I assume go to the resistor?  If I have power going to this brand new relay, do I have a defective relay or is the interior controls causing a problem where even in the off state (for the controls) - the fan would still not run with ignition key on?