montecarlo4

My blower fan never comes on. I check the pos and neg wire at the blower motor, and i get 12v. So i ran a wire directly from the battery positive to the blower motor and it comes to life. So, is the wire from the HVAC controls not sending enough amps for the blower motor or...?
what should i check next?
thanks
matt

gilsfour

What year? Manual or electronic controls?

rodj

If you have manual HVAC then power goes through a relay .It may be faulty

sailorsteve

Without knowing the details requested in the previous post...

I assume you have checked fuses, right?

Next, you need to identify which wire supplies juice from the controller to the motor. Set the controls so that the fan should come on (try "defrost") and test for voltage at that wire (Key on, of course). You may need a wiring diagram to determine the color code. If no power at that point, trace the circuit backwards to see where the fault lies.

montecarlo4

i have a 1984 so i assume manual?
there are two wires going to blower motor, one pos and one neg. I get 12 volts at those 2 wires when the switch is turned on.
thanks
matt

MissileDoc

there are two wires going to blower motor, one pos and one neg. I get 12 volts at those 2 wires when the switch is turned on.

Matt, if you are taking a voltage reading from your "pos" wire to a known good ground and then a voltage reading from your "neg" wire to a known good ground and read 12 volts DC on each wire, your "neg" wire is not making a good connection to ground.

This is assuming you have the wires connected to the blower motor and the fan switch is set to ON. If this is the case, 12 volts DC is being supplied to your fan motor through the "pos" wire where it sits on the motor windings and and also on the "neg" wire since there is not a good ground present to complete the electrical circuit.

Sandpiper59

If you're using a meter without a load then the 12v can show up through even the worst connection. Load that 12v down using a 12v trouble light or even a spare interior light or tail light bulb. Just about any bulb will draw less than the fan normally would but will draw enough to drop that 12v to 1v or 2v if there is a connection or ground issue. If you now have way less than 12v you can chase that.

Greg

sailorsteve

If you have identified the negative wire at the fan, check the resistance between that wire and a known good ground. The reading should be zeroish. If it is higher, as stated previously, there is a grounding issue. On the positive side, there may be an issue with high resistance thru the switch. I suspect one of these two things is your problem, as you have ruled out the motor itself.

gilsfour

I think you could use Sandpiper's or Sailorsteve's approach and isolate the cause. If you only ran one wire from the battery to the fan motor , then it's likely that the resistance in the switch is too high.

sailorsteve

Another possibility...

Later model HVAC systems will not enable the fan until the coolant temp is up. Not sure if this is the case on your '84, but if so, there may be erroneous input to the HVAC system due to a faulty coolant sensor. Time to consult the FSM.

montecarlo4

the blower switch, hvac switch and lights use the same 12 v source and same grounding source, correct?

thanks for the help i should get a chance to look at it this weekend
matt

montecarlo4

i was able to work on my prob recently

i ohlmeda(sp) the switch, and it had zero resistance at each fan setting

i than thought it was the relay, since i could apply 12 v to the blue and orange wire and the blower motor would operate, but new relay didnt help.

my question is now. there are 4 wires going to blower switch. 1 is 12v and the other 3 take 12 volts to blower motor? but they appear to go to a switch in the heater core housing in the engine bay? could that connection be bad, how can i test it?
thanks
matt

vetteoz

That is the resistor bank that gives you the lower blower speeds.
The resistors are in the air flow top keep them cool

gilsfour

If I understand correctly, 1) the fan motor runs if you connect the positive side of the motor directly to the positive side of the battery and 2) your voltmeter reads 12v across the fan motor when the fan switch is on.

After looking at the wiring diagram provided by Vetteoz, I believe the fan motor is properly grounded. Otherwise, it would not run when connected directly to the battery. If, however, the fan relay itself is not properly grounded, the fan motor wouldn't run with the fan switch turned on. I'd make sure the relay has a good ground.

montecarlo4

is there anyway to test the relay?
thanks
matt

rodj

As diagram shows ; there is a power path to blower when relay not energized ( no ground )

If no ground for the relay then it won't change over when Hi speed selected
Default off position of the relay is in the NC position as shown which would give the lower blower speeds
( if resistors / wiring working correctly ) but not full speed where the relay changeover gives power direct from batt to blower motor

jfb

A voltmeter draws so little current that measuring the voltage on the blower motor wires (motor not connected) can read 12v but the motor speed circuit will not supply enough current to operate the motor. You should measure the motor voltage with the motor connected. Since the motor won't run connected, you clearly will measure very very low voltage, probably zero. Check the ac fuse with an ohmeter (they see better than your eyes do!). Then check with a 12v lamp for voltage (lamp lights) on each wire on the blower switch with the ign in run and the blower switch in each position, then check for 12v on the blue wire on the relay with the blower sw in low and see if the blower relay closes with the blower sw in hi and if it does, see if there is 12v on the motor and the motor running at high speed. If you will look at the schematic vetteoz provided, you will see my instructions follows power from the fuse through the blower speed switch and blower relay to the motor. Somewhere in that circuit the motor current is interrupted.

montecarlo4

finally got a chance to follow the instructions provided.
For some reason, the blower motor begin working on the low speeds just not on the high speed. So, with a vm, i am getting 12 volts on the red wire all the time until i turn on the high. The blue wire is getting volts depending on the blower switch. The orange wire only gets power when the high is turned on, but the blower does not engage with it set on high. What next?
thanks
matt

hooked073

A fast quess with what you re describing is bad blower motor resistor or connection at resistor. Very comman 12 bucks at just about any parts store

montecarlo4

i got a new resistor, and same problems. low speed but no high speed. So i started all over checking connections. The switch is fine, it test fine. I get 12v to the orange wire when switch is on high, but nothing through relay, so i thought maybe the new relay is bad, the parts store let me exchange it. And now when i turn on high speed it blows the fuse. I think now the blower motor must have an internal short?
thanks
matt