73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Interior & Equipment => Heating, Ventilation & Air Conditioning (HVAC) => Topic started by: 79diesel on April 15, 2008, 11:27:54 am
-
does anyone have a heat/AC wiring diagram for a 79? In my rewiring i seem to have ended up with constant power to the yellow wire to the heater resistors which results in the heater fan drawing 1 amp when its off.
thanks
-
The fan always is on for these trucks.
-
so if you leave the fan on when you shut the truck off it should stay on? that doesnt sound right to me.. my 86 is not like that and it definitely doesnt have power all the time to this wire.
right now when the fan is in the off position it still draws an amp and will drain my battery. I know the red power wire that feeds the fan should be constant because it is controlled by the relay but the yellow wire that goes to the resistors and then to the relay with a dark blue wire should not have power.
Im pretty sure i accidently hooked the power wire to the fan selector using a constant power instead of a switched power but i dont know the colour of that wire so it would be hard to trace it without taking my dash apart.
-
That should be key on B+ for the switch. That's most likely your problem. I posted a diagram a few months ago on here. did you try to search yet?
-
ah yes the search is a wonderful overlooked feature lol i found it...its to dark to look at the truck now though...ill have a look tomorrow
thanks
-
I thought you were talking about with the switch forward...
-
ok heres the diagram you posted
(http://img.photobucket.com/albums/v233/high_octane94/heatac.gif)
the brown/white wire from the selector to the resistor is yellow on my truck. this wire has power all the time even when the truck is off and when the fan is in the off position which feeds the fan 12V and 1 amp (motor does not operate with only 1 amp) . This would be because the brown wire to the selector has constant power right?
-
What do you mean the motor does not operate with 1 amp? How did you measure the current flow?
-
brown wire to the selector has constant power right?
yep, that would do it. Is that the case? If you take the brown wire loose at the fuse block, does the amp-draw stop?
If the brown wire is energized as you say, then the fan would be turning low speed.
V=IR so V/R=I So at the motor, check V from motor lead to gnd divide by R (Ohms) from motor lead to B+ and that will be your amp draw.
-
i checked current flow using a multimeter..it is actually .9A i guess this is because there is no actual "off" position for the fan speed selector?.. i cant hear it turning but i guess it could be slowly. it works fine when the key is in the on position.
Ok so i need a lesson here. Where does the fuse panel get the switched power from? which wire into the fuse panel should be switched for the heater? Right now there are two B+ wires to the fuse panel from the engine bay, a red and a brown. I havent touched anything after the fuse panel so im thinking it must be before it
-
Where did you measure the current draw? Did you open the circuit and install the meter in series? In other words you unplugged the wire at the blower motor and installed your meter leads one touching the blower terminal M+ and the other touching the wire.
-
yes
-
So then if you series the meter in between the switch and unplug the connector at the motor current flow is zero?
-
with the motor unplugged and the meter in series between the switch and the resistor there is no current flow
-
Then that tells you it's the motor drawing the current so again make the power source to your control assembly switched B+ from the fuse panel.
-
thats what i was thinking but which wire is the power source to to the fuse panel for the heater?
-
In the schematic it's the brown wire. your truck may be different color but do you see where it says fused ign feed 3? The fuse panel has a bussed connection that is energized by the ign switch. If your factory harness is hacked then just run a fused power feed switched from the fuse block,.
-
ok awesome thanks