1985 Corvette Blower Motor Problem - Half diagnosed
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
1985 Corvette Blower Motor Problem - Half diagnosed
Hello everyone. I'm having some trouble proceeding to the next step in my diagnostics of my blower motor not coming on. I only noticed this problem about an hour ago.
When I turn the A/C to MAX, the compressor clutch comes on and the blower motor does nothing. When I switch to Vent, the clutch turns off and the blower motor still does nothing.
- I have ground at the blower motor with the key OFF.
- I have power at the blower motor when the key is ON AND when I choose an HVAC setting.
-(This is the important part) I have power at the blower motor with the key ON 12 volts appears at the GROUND wire, even when the ground wire is disconnected from the blower motor.
When I use a power probe to apply ground to the ground terminal of the blower motor, the blower motor turns on.
I figured maybe there was a hot short to the ground wire for the blower motor. I removed each fuse one at a time with no change.
Does anyone know what could be the cause of this?
Thanks!
When I turn the A/C to MAX, the compressor clutch comes on and the blower motor does nothing. When I switch to Vent, the clutch turns off and the blower motor still does nothing.
- I have ground at the blower motor with the key OFF.
- I have power at the blower motor when the key is ON AND when I choose an HVAC setting.
-(This is the important part) I have power at the blower motor with the key ON 12 volts appears at the GROUND wire, even when the ground wire is disconnected from the blower motor.
When I use a power probe to apply ground to the ground terminal of the blower motor, the blower motor turns on.
I figured maybe there was a hot short to the ground wire for the blower motor. I removed each fuse one at a time with no change.
Does anyone know what could be the cause of this?
Thanks!
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
Hello everyone. I'm having some trouble proceeding to the next step in my diagnostics of my blower motor not coming on. I only noticed this problem about an hour ago.
When I turn the A/C to MAX, the compressor clutch comes on and the blower motor does nothing. When I switch to Vent, the clutch turns off and the blower motor still does nothing.
- I have ground at the blower motor with the key OFF.
- I have power at the blower motor when the key is ON AND when I choose an HVAC setting.
-(This is the important part) I have power at the blower motor with the key ON 12 volts appears at the GROUND wire, even when the ground wire is disconnected from the blower motor.
When I use a power probe to apply ground to the ground terminal of the blower motor, the blower motor turns on.
I figured maybe there was a hot short to the ground wire for the blower motor. I removed each fuse one at a time with no change.
Does anyone know what could be the cause of this?
Thanks!
When I turn the A/C to MAX, the compressor clutch comes on and the blower motor does nothing. When I switch to Vent, the clutch turns off and the blower motor still does nothing.
- I have ground at the blower motor with the key OFF.
- I have power at the blower motor when the key is ON AND when I choose an HVAC setting.
-(This is the important part) I have power at the blower motor with the key ON 12 volts appears at the GROUND wire, even when the ground wire is disconnected from the blower motor.
When I use a power probe to apply ground to the ground terminal of the blower motor, the blower motor turns on.
I figured maybe there was a hot short to the ground wire for the blower motor. I removed each fuse one at a time with no change.
Does anyone know what could be the cause of this?
Thanks!
The blower motor wiring diagram for the 85 is below, you can see the power goes via the resistors to the blower motor relay.
Just run a wire from the battery + to the blower motor and see if it runs, if it does it is the relay or resistors. If it doesn't work, run a ground - from the battery to the blower motor ground to test the ground.
Last edited by gerardvg; May 29, 2015 at 06:49 AM.
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Hi
The blower motor wiring diagram for the 85 is below, you can see the power goes via the resistors to the blower motor relay.
Just run a wire from the battery + to the blower motor and see if it runs, if it does it is the relay or resistors. If it doesn't work, run a ground - from the battery to the blower motor ground to test the ground.
The blower motor wiring diagram for the 85 is below, you can see the power goes via the resistors to the blower motor relay.
Just run a wire from the battery + to the blower motor and see if it runs, if it does it is the relay or resistors. If it doesn't work, run a ground - from the battery to the blower motor ground to test the ground.
I got a little further into it now and I suspect that the problem is a corroded ground splice or main ground connection.
The 12 volts coming on the ground wire for the blower motor is coming from the D terminal on the relay. It is going through the winding in the relay out to the C terminal and all the way through the ground circuitry because there is no actual ground connection.
When I unplug the relay, the 12 volts stops showing up at the ground terminal of the blower motor, and it shows that there is ground there. When I power up the blower motor manually with 12 volts with the relay disconnected, nothing happens.
If I connect everything together and manually apply ground to circuit number 150, everything works.
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 276
From: Melbourne, Victoria, Australia
Thanks for the diagram.
I got a little further into it now and I suspect that the problem is a corroded ground splice or main ground connection.
The 12 volts coming on the ground wire for the blower motor is coming from the D terminal on the relay. It is going through the winding in the relay out to the C terminal and all the way through the ground circuitry because there is no actual ground connection.
When I unplug the relay, the 12 volts stops showing up at the ground terminal of the blower motor, and it shows that there is ground there. When I power up the blower motor manually with 12 volts with the relay disconnected, nothing happens.
If I connect everything together and manually apply ground to circuit number 150, everything works.
I got a little further into it now and I suspect that the problem is a corroded ground splice or main ground connection.
The 12 volts coming on the ground wire for the blower motor is coming from the D terminal on the relay. It is going through the winding in the relay out to the C terminal and all the way through the ground circuitry because there is no actual ground connection.
When I unplug the relay, the 12 volts stops showing up at the ground terminal of the blower motor, and it shows that there is ground there. When I power up the blower motor manually with 12 volts with the relay disconnected, nothing happens.
If I connect everything together and manually apply ground to circuit number 150, everything works.
The ground wires are above the oil filter, perhaps remove the bolt clean the block and reconnect. That may solve it, i think there are more ground wires on the trans bellhousing to engine bolt.
If you get stuck just run a fresh wire to ground.
3rd Gear
Joined: Oct 2020
Posts: 3
Likes: 1
Tested, tested and tested, nothing...
Hello, I don't know if anyone is still monitoring this thread.
My blower motor stopped working about a week or so ago. Since then, I've ordered a new fan (it does not turn on), I've ordered a new HVAC controller (the center-console control center)? It comes on, shows temp, fan speeds, other indicators, but still no fan.
I took out my volt meter and tested the outer connections to the blower (red and black?) and I got 12v. I tried keeping one probe on positive and tested the middle connector and I'm not sure what reading I'm getting. It looks like .5 volts? It doesn't appear to change if I adjust the fan speed. I also removed fuse 28 under the hood and retested the connections -- when no fuse, no 12v. I've also checked the two fuses in the footwell fuse box.
Is there another controller somewhere that might be bad? Anything else I should be checking?
I saw someone mentioned the ground point. I haven't jacked my car up yet, but is it fairly accessible and easy to locate? Any chance someone has a picture? I may try cleaning that up and checking the state of the wires going to it.
If all else fails -- is there an option for some kind of external controller I can rig up?
My blower motor stopped working about a week or so ago. Since then, I've ordered a new fan (it does not turn on), I've ordered a new HVAC controller (the center-console control center)? It comes on, shows temp, fan speeds, other indicators, but still no fan.
I took out my volt meter and tested the outer connections to the blower (red and black?) and I got 12v. I tried keeping one probe on positive and tested the middle connector and I'm not sure what reading I'm getting. It looks like .5 volts? It doesn't appear to change if I adjust the fan speed. I also removed fuse 28 under the hood and retested the connections -- when no fuse, no 12v. I've also checked the two fuses in the footwell fuse box.
Is there another controller somewhere that might be bad? Anything else I should be checking?
I saw someone mentioned the ground point. I haven't jacked my car up yet, but is it fairly accessible and easy to locate? Any chance someone has a picture? I may try cleaning that up and checking the state of the wires going to it.
If all else fails -- is there an option for some kind of external controller I can rig up?
